WO2025221548A1 - Medical device system and method for dynamically displaying implantable medical device position - Google Patents

Abstract

A medical device system includes processing circuitry configured to receive an orientation sensor signal responsive to changes in a position of an implantable medical device relative to a reference vector. The processing circuitry may be configured to, for each of a plurality of time points, compute from the first orientation signal an angular position of the implantable medical device relative to the reference vector and determine a corresponding directional difference to the angular position from a preceding angular position. The medical device system may include a display unit configured to display a moving graphic image of the implantable medical device according to the computed angular positions and directional differences.

Description

MEDICAL DEVICE SYSTEM AND METHOD FOR DYNAMICALLY DISPLAYING IMPLANTABLE MEDICAL DEVICE POSITION

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of provisional U.S. Patent Application No. 63/636.704, filed on April 19, 2024, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] This disclosure relates to a medical device system and method for determining a position of an implantable medical device and dynamically displaying the position.

BACKGROUND

[0003] A variety of medical devices for delivering a therapy and/or monitoring a physiological condition have been used clinically or proposed for clinical use in patients. Examples include medical devices that deliver therapy to and/or monitor conditions associated with the heart, muscles, nen es, brain, stomach or other organs or tissue or a patient. Some medical devices may employ one or more electrodes for the delivery of therapeutic electrical signals to such organs or tissues and/or one or more electrodes for sensing intrinsic electrical signals within the patient that are generated by such organs or tissue. Similarly, some medical devices may additionally or alternatively include one or more other sensors for sensing physiological parameters of a patient. [0004] For example, some medical devices may function as cardiac pacemakers or cardioverterdefibrillators that provide therapeutic electrical signals to the patient’s heart. In some examples, a medical device may sense intrinsic depolarizations of the heart and thereby control delivery of therapeutic signals to the heart based on the sensed depolarizations. Upon detection of an abnormal rhythm, such as bradycardia, tachycardia, or fibrillation, an appropriate therapeutic electrical signal or signals may be delivered to restore or maintain a more normal heart rhythm. For example, in some cases, an implanted medical device may deliver pacing stimulation to the heart of the patient upon detecting tachycardia or bradycardia, and/or deliver cardioversion or defibrillation shocks to the heart upon detecting fibrillation.

[0005] Advancement to and positioning of a medical device at a desired implant site can require fluoroscopic imaging or other imaging to confirm the anatomical location of the implantable medical device, which can expose the patient and clinical staff to radiation. In some cases, electrophysiological testing or other testing may be required to confirm that the medical device is at a desired implant site and in an acceptable position.

SUMMARY

[0006] The techniques of this disclosure provide a medical device sy stem and method for determining a position of an implantable medical device (IMD) of the medical device system and dynamically displaying the position, which may be in real time. The IMD may include a three- dimensional (3D) orientation sensor, e.g., an accelerometer. The acceleration signals received from a 3D accelerometer can be used for determining the position of the IMD relative to gravity and earth center. The acceleration signals may be used for determining the pitch and roll of the IMD. for example. The position of the IMD can be rendered graphically for display on a graphical user interface. The position of the IMD can be adjusted dynamically as a clinician moves the IMD so that the orientation of the IMD relative to earth center can be observed by the clinician, without line of sight or requiring other imaging equipment or methods.

[0007] In one example, the disclosure provides a medical device system including processing circuitry configured to receive an orientation signal that is a three dimensional signal responsive to changes in a position of an implantable medical device relative to a reference vector. For each of a plurality of time points, the processing circuitry may compute, from the orientation signal, an angular position of the implantable medical device relative to the reference vector. For each of the computed angular positions, the processing circuitry may determine a corresponding directional difference to the angular position from a preceding angular position computed for a preceding time point of the plurality⁷ of time points. The medical device system may further include a display unit configured to display a graphic image of the implantable medical device in a starting position relative to a local coordinate system. The display unit may be configured to dynamically adjust the graphic image of the implantable medical device from the starting position to the angular positions computed consecutively for the plurality of time points by rotating the graphic image of the implantable medical device between each of the consecutively computed angular positions in a clockwise or counterclockwise direction according to each of the respective corresponding directional differences.

[0008] In another example, the disclosure provides a method comprising receiving an orientation signal that is a three dimensional signal responsive to changes in a position of an implantable medical device relative to a reference vector. The method may include, for each of a plurality of time points, computing an angular position of the implantable medical device relative to the reference vector from the orientation signal. The method may further include, for each of the computed angular positions, determining a corresponding directional difference to the angular position from a preceding angular position computed for a preceding time point of the plurality of time points. The method may include displaying a graphic image of the implantable medical device in a starting position relative to a local coordinate system. The method may further include dynamically adjusting the graphic image of the implantable medical device from the starting position to the angular positions computed consecutively for the plurality' of time points by rotating the graphic image of the implantable medical device between each of the consecutively computed angular positions in a clockwise or counterclockwise direction according to each of the respective corresponding directional differences.

[0009] In another example, the disclosure provides a non-transitory. computer-readable storage medium storing a set of instructions which, when executed by processing circuitry of a medical device system, cause the medical device system to receive an orientation signal that is a three dimensional signal responsive to changes in a position of an implantable medical device relative to a reference vector and, for each of a plurality of time points, compute an angular position of the implantable medical device relative to the first reference vector from the orientation signal. The instructions may further cause the medical device system to, for each of the angular positions, determine a corresponding directional difference to the angular position from a preceding angular position computed for a preceding time point of the plurality of time points. The instructions may further cause the medical device system to display a graphic image of the implantable medical device in a starting position relative to a local coordinate system. The instructions may further cause the medical device system to dynamically adjust the graphic image of the implantable medical device from the starting position to the angular positions computed consecutively for the plurality’ of time points by rotating the graphic image of the implantable medical device between each of the consecutively computed angular positions in a clockwise or counterclockwise direction according to each of the respective corresponding directional differences.

[0010] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 is a conceptual diagram illustrating an implantable medical device (IMD) system that may be configured to perform the techniques disclosed herein.

[0012] FIG. 2 is a conceptual diagram of the IMD show n in FIG. 1.

[0013] FIG. 3 is a diagram of a delivery tool loaded with IMD of FIG. 2 prior to deployment of the IMD at an implant site.

[0014] FIG. 4 is a diagram of a medical device system including an IMD provided with a different fixation member and electrodes than the IMD shown in FIG. 2.

[0015] FIG. 5 is a diagram of the IMD of FIG. 4.

[0016] FIG. 6 is a diagram of the IMD of FIG. 4 loaded in a delivery tool prior to deploy ment at an implant site.

[0017] FIG. 7 is a diagram of an example configuration of an IMD of a medical device system configured to perform the techniques disclosed herein according to some examples.

[0018] FIG. 8 is a flow- chart of a method that may be performed by a medical device system for determining dynamic IMD positional data according to some examples.

[0019] FIG. 9A is a diagram depicting an image of an IMD in a nominal starting position according to some examples.

[0020] FIG. 9B is a diagram depicting an image of the IMD show n in FIG. 9A after rotation of the IMD to a determined pitch angle.

[0021] FIG. 10A is a diagram depicting an image of an IMD in a graphical user interface (GUI) in the same position as shown in FIG. 9B.

[0022] FIG. 10B is a diagram depicting an image of the IMD show n in FIG. 10A after rotation of the IMD around its longitudinal axis.

[0023] FIG. 11 is a flow chart of a method performed by processing circuitry of a medical device system for determining IMD positional information and providing feedback to a user during an implant procedure according to some examples.

[0024] FIG. 12 is a diagram of an image that may be displayed in a GUI by a display unit of a medical device system according to some examples.

[0025] FIG. 13 is a flow chart of a method for determining IMD positional information and generating a dynamic image of IMD position according to another example.

[0026] FIG. 14 is a diagram of a patient depicting a method for establishing a reference vector for a secondary sensor of a medical device orientation sensor according to some examples.

[0027] FIGs. 15 A — 15C are diagrams depicting a method for determining the yaw angle of an IMD using a combination of 3D orientation sensor signals according to some examples. [0028] FIG. 16 is a diagram of a patient depicting another method for establishing a reference vector for a secondary sensor of a medical device orientation sensor according to another example.

[0029] FIG. 17 is a diagram of a processing circuit configured to analyze IMD positional data for determining a dislodgement risk of an IMD at an implant site according to some examples. [0030] FIG. 18 is a diagram of a GUI that may be displayed by an external device display unit of a medical device system including a dislodgment risk determined by the dislodgement risk predictor of FIG. 17.

[0031] FIG. 19 is a diagram of a medical device system that may be configured to perform the techniques disclosed herein according to another example.

DETAILED DESCRIPTION

[0032] This disclosure relates to a medical device system and techniques for determining a position of an IMD based on orientation sensor signals from a 3D sensor, e.g., based on acceleration signals from a 3D accelerometer, of the IMD. The IMD position relative to earth center can be determined based on acceleration signal components. For example, the IMD pitch and roll may be determined relative to earth center. The IMD position can be rendered graphically to provide a real time moving image of the IMD position relative to earth center to inform a clinician of the IMD position without requiring other imaging equipment or methods, such as fluoroscopy. Evaluation of the motion of the IMD based on time domain analysis of the IMD position can be performed to assess IMD fixation in some examples.

[0033] FIG. 1 is a conceptual diagram illustrating an IMD system 10 that may be configured to perform the techniques disclosed herein. The illustrative examples provided herein generally relate to cardiac devices, e.g., cardiac monitors or cardiac pacemakers, used to sense cardiac signals and/or deliver electrical stimulation therapy to a patient’s heart. It is to be understood, however, that the techniques disclosed herein may be implemented in a wide variety of IMD systems that include an IMD having a 3D orientation sensor, e.g.. an accelerometer responsive to changes in the IMD orientation relative to gravity. Among the IMDs that may be included in a medical device system configured to perform the techniques disclosed herein are, with no limitation intended, cardiac monitors, cardiac pacemakers, cardioverter-defibrillators, neurostimulators (e.g., brain stimulators, spinal cord stimulators, sensory or autonomic nerve stimulators, etc.), muscular or neuromuscular stimulators (e.g., gastric stimulators, diaphragm stimulators, skeletal muscle stimulators or somatic nerve stimulators, etc.), drug pumps, cardiac assist devices such as artificial heart or left ventricular assist devices, and other sensors or monitors such as glucose monitors, tissue or blood oxygen monitors, etc. The techniques disclosed herein may be implemented in a medical device system including an IMD configured to be implanted without direct line of sight, e.g., via a delivery tool or catheter that is navigated to an implant site.

[0034] Furthermore, it is to be understood that the techniques disclosed herein may be implemented in a medical electrical lead, pressure catheter, guide catheter, or other elongated medical device having a distal end that is advanced to an internal body location. The proximal end may remain outside the patient’s body or may be connected to an implanted medical device such as a pacemaker, cardioverter-defibrillator, neurostimulator or any of the other example implantable devices listed above. The elongated medical device having at least its distal end implanted, temporarily or chronically, may include an orientation sensor at or near its distal end, such as at least one accelerometer, for determining positional data of the distal end of the elongated medical device according to the techniques disclosed herein. The elongated medical device may be a steerable device advanced over a guidewire or retained within a steerable delivery tool (such as a medical electrical lead advanced through a guide catheter) so that its distal end may be positioned at different pitch, roll and yaw angles.

[0035] For example, the IMD 14 shown in FIG. 1 is a leadless pacemaker that can be implanted wholly within a patient’s heart 8. As further described below, the IMD 14 may be advanced to an implant site in or on the patient’s heart using a delivery tool. IMD 14 may be rotated and/or advanced from the delivery tool at the implant site and anchored to the implant site via one or more fixation members. The position of IMD 14, during the implant procedure and/or after an implant procedure can be determined using the techniques disclosed herein. For instance, positional changes of IMD 14 occur when a clinician is advancing and/or rotating the IMD during an implant procedure and, after the implant procedure, the IMD position can change dynamically due to cyclical cardiac motion, respiratory motion or other patient body motion. The disclosed techniques provide a method for dynamically displaying the position of IMD 14, which may be in real time, to provide clinician guidance during an implant procedure and/or assessing the position and fixation of IMD 14 post-implant.

[0036] IMD system 10 includes an IMD 14 configured to communicate with an external device 50 via a wireless communication link 55. In the example shown, IMD 14 is a leadless, transcatheter intracardiac pacemaker adapted for implantation wholly w ithin a heart chamber, e.g., wholly within the right ventricle (RV), wholly within an atrium (e.g., the right atrium (RA) or left atrium), or wholly within the left ventricle (LV) of heart 8 for sensing cardiac signals and delivering ventricular pacing pulses. IMD 14 may be reduced in size compared to subcutaneously implanted pacemakers and may be generally cylindrical in shape to enable transvenous implantation via a delivery catheter. IMD 14 is shown positioned in the RV, along an endocardial wall, e.g., near the RV apex though other locations are possible. In other examples, IMD 14 may be implanted along the interventricular septum for delivering cardiac pacing to the septal myocardium and/or a portion of the native His-Purkinje conduction system of the heart 8, e.g., in the area of the His bundle, the left bundle branch or the right bundle branch. IMD 14 may be positioned in or on (e.g., epicardially) the RV, LV, RA or left atrium of heart 8. In the example shown, IMD 14 is positioned within the RV to provide ventricular pacing and cardiac signal sensing.

[0037] IMD 14 may be capable of producing electrical stimulation pulses, e.g.. pacing pulses, delivered to heart 8 via one or more electrodes on the outer housing of the pacemaker. IMD 14 is configured to deliver pacing pulses and sense a cardiac electrical signal using housing based electrodes for producing a cardiac electrogram (EGM) signal. The cardiac electrical signals may be sensed using the housing based electrodes that are also used to deliver pacing pulses to the heart 8.

[0038] IMD 14 may be configured to control the delivery of pacing pulses according to one or more pacing modes, e.g., an atrial asynchronous ventricular pacing mode or in an atrial synchronous ventricular pacing mode. For example. IMD 14 may sense acceleration signals that are responsive to cardiac motion from a 3D accelerometer included in IMD 14. IMD 14 may sense atrial motion from the accelerometer signals for enabling IMD 14 to deliver ventricular pacing pulses synchronous to atrial contractions to promote normal synchrony between atrial activation and ventricular activation. A 3D accelerometer used for determining IMD position and generating a dynamic display of the IMD position according to techniques disclosed herein can be used by IMD 14 for detecting cardiac mechanical event signals. The cardiac mechanical event signals, e.g., attendant to cardiac systole and/or cardiac diastole, can be used for determining the heart rhythm and controlling cardiac pacing by IMD 14. IMD 14 may deliver ventricular pacing pulses at a desired atrioventricular (AV) pacing interval after atrial contractions that are sensed from an acceleration signal, for example. The cardiac mechanical event signals can be used to identify cardiac cycles to facilitate assessment of IMD positional changes over a cardiac cycle in some examples.

[0039] IMD 14 may be capable of bidirectional wireless communication with external device 50 for programming operating parameters and algorithms into IMD 14, e.g.. pacing control parameters, cardiac signal sensing parameters, etc. External device 50 may be a dedicated IMD programmer used by a physician, technician, nurse, clinician or other qualified user for programming operating parameters in IMD 14. External device 50 may be located in a clinic, hospital or other medical facil i ty. External device 50 may alternatively be embodied as a home monitor or a handheld device that may be used in a medical facility, in the patient’s home, or another location. In some examples, external device 50 may be a personal device such as a mobile phone, tablet, personal computer or other device capable of wireless communication with IMD 14.

[0040] External device 50 includes a processor 52, memory 53, display unit 54, user interface 56 and telemetry unit 58. Telemetry' unit 58 may be configured for bidirectional communication with communication circuitry included in IMD 14. IMD 14 may include a communication circuit configured for radiofrequency distance telemetry and/or short range induction communication, as examples, with external device 50. External device telemetry unit 58 may include a transceiver and antenna configured for bidirectional communication with the communication circuit included in IMD 14.

[0041] Telemetry’ unit 58 is configured to operate in conjunction with processor 52 for sending and receiving data relating to IMD functions via communication link 55. According to techniques disclosed herein, external device 50 may receive orientation sensor signals and/or data derived therefrom from IMD 14 via telemetry' unit 58. Processor 52 may determine dynamic IMD positional information from the received data for generating a moving, graphical image of IMD 14. The dynamic positional information may be used to generate the graphical image of IMD 14 on display’ unit 54 in a real-time display. At other times, the dynamic positional information may be used to generate the moving, graphical image of IMD 14 in a postprocessing method for displaying to a user IMD position over a cardiac cycle or other time interval.

[0042] Telemetry unit 58 may establish wireless communication link 55 with IMD 14 using a radio frequency (RF) link such as BLUETOOTH®, BLUETOOTH® Low Energy (BLE), Wi-Fi, Medical Implant Communication Service (MICS) or other communication bandwidth. In some examples, external device 50 may include a programming head 51 that is placed proximate IMD 14 to establish and maintain a communication link 55 with IMD 14 via an antenna of IMD 14, and in other examples external device 50 and IMD 14 may be configured to communicate using a distance telemetry’ algorithm and circuitry⁷ that does not require the use of a programming head and does not require user intervention to maintain a communication link.

[0043] When programming head 51 is included, programming head 51 may include a user interface device 57 that can be controlled by external device 50 to provide user feedback signals indicative of qualitative positional information of IMD 14, e.g., during an implant procedure. As described below, angular positions of IMD 14 relative to a reference vector, e.g., gravity, can be determined by processing circuitry’ of the medical device system 10 from orientation sensor signals. Programming head user interface device 57 may include light emitting diodes (LEDs), speakers, vibrating devices, or other devices configured to display, broadcast or emit user feedback signals indicative of the qualitative positional information of IMD 14. The qualitative positional information may indicate when an angular position measurement of the position of IMD 14 relative to gravity (or another reference vector of an orientation sensor of IMD 14) meets a recommended range for a given implant location of IMD 14.

[0044] While not explicitly shown in FIG. 1, it is to be understood that in some examples, a second co-implanted IMD may function as a relay device for transmitting/receiving communication signals between IMD 14 and external device 50. As such, external device 50 may receive communication signals directly or indirectly from IMD 14. Communication link 55 may represent a direct communication link in some examples. Communication link 55 may represent an indirect communication link between IMD 14 and external device 50 that includes one or more relay devices (e.g., one or more co-implanted IMDs) that facilitate data transfer between IMD 14 and external device 50 in other examples.

[0045] Processor 52 is coupled to the other components and units of external device 50, e.g., via a data bus, for controlling the functions attributed to external device 50 herein. Processor 52 may execute instructions stored in memory 53. Processor 52 may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or equivalent discrete or analog logic circuitry. In some examples, processor 52 may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to processor 52 herein may be embodied as software, firmware, hardware or any combination thereof. Memory 53 may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), nonvolatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other digital or analog media. Memory 53 may include non-transitory computer-readable media that may store instructions that, when executed by processor 52, cause medical device system 10 to perform various methods and functions attributed to medical device system 10 as disclosed herein, alone or in combination with processing circuitry of IMD 14.

[0046] User interface unit 56 may include display unit 54 and a mouse, touch screen, keypad or the like to enable a user to interact with external device 50, e.g., to initiate and terminate an interrogation session for retrieving data from IMD 14, adjust settings of display unit 54, enter programming commands or selections or make other user requests. Display unit 54, which may include a liquid crystal display, light emitting diodes (LEDs) and/or other visual display components, may generate a display of cardiac electrical signals received from IMD 14 and/or data derived therefrom. Display unit 54 may be configured to generate a graphical user interface (GUI) including various windows, icons, user selectable menus, etc. to facilitate interaction by a user with the external device 50 and IMD 14. As described below, display unit 54 may display a dynamic graphical rendering of the position of IMD 14 relative to earth center, which may be in real time, for guiding a clinician or other user in positioning IMD 14 and/or assessing fixation of IMD 14 at an implant site.

[0047] Display unit 54 may function as an input and/or output device using technologies including liquid crystal displays (LCD), quantum dot display, dot matrix displays, light emitting diode (LED) displays, organic light-emitting diode (OLED) displays, cathode ray tube displays, e-ink, or monochrome, color, or any other type of display capable of generating tactile, audio, and/or visual output. In some examples, display unit 54 is a presence-sensitive display. Display unit 54 may serve as a user interface device that operates both as one or more input devices and one or more output devices.

[0048] It is contemplated that external device 50 may be in wired or wireless connection to a communications network via a telemetry circuit that includes a transceiver and antenna or via a hardwired communication line for transferring data to a centralized database or computer to allow remote management of the patient. For example, external device telemetry⁷ unit 58 may be coupled to a communication network/cloud 75 for receiving and transmitting data to a computing device 74, which may be a personal computer, personal mobile device or other computing device at a remote location from the patient to enable remote monitoring of data obtained from IMD 14 by a clinician or other user. Remote patient management systems including a centralized patient database, e.g., stored on network/cloud 75, may be configured to utilize the presently disclosed techniques to enable a clinician to view cardiac signals, sensor signals, and therapy delivery related data and other device related data and authorize remote programming of IMD 14.

[0049] In some examples, external device 50 may transmit or upload signals sensed by IMD 14 and/or data derived therefrom to a centralized database for cloud-based processing and/or for rendering a dynamic display of the position of IMD 14 on a remote computer or other device for viewing by a clinician or other user. In this way, a clinician may remotely assess the dynamically changing position of IMD 14 during an implant procedure and/or post-implant, e.g., as orientation sensor signals are sensed in real time by IMD 14 or during a post-processing analysis of stored acceleration signal data.

[0050] The CARELINK™ network available from Medtronic, Inc., Dublin, Ireland, is an example of a remote patient monitoring system and database that may collect and display data obtained from IMD 14. Processing circuitry of the medical device system 10. e.g., any combination of one or more of external device processor 52, network/cloud 75, computing device 74 and/or processing circuitry included in IMD 14 (see FIG. 7), may cooperatively perform methods disclosed herein for computing and displaying IMD positional data. As described below in conjunction with FIG. 17 and FIG. 18, data received from IMD 14 and external device 50 may be analyzed by cloud-based algorithms for determining a dislodgement risk that may be presented in a GUI for review by a clinician or other user.

[0051] FIG. 2 is a conceptual diagram of IMD 14 show n in FIG. 1. IMD 14 includes a housing 15 that encloses IMD circuitry, e.g., sensing circuitry, pulse generating circuitry control circuitry, communication circuitry, and a power source as further described below in conjunction with FIG. 7. Housing 15 includes a longitudinal sidewall 17 extending between a distal end 26 and a proximal end 28, which may collectively define a hermetically sealed interior volume of IMD 14. Housing 15 may carry one or more electrodes 16 and 18 spaced apart along the housing 15 for sensing cardiac electrical signals and delivering pacing pulses. Electrode 16 is shown as a tip electrode extending from or positioned on distal end 26. Electrode 18 is shown as a ring electrode along a mid-portion of longitudinal sidewall 17, for example adjacent proximal end 28. Electrode 18 may be referred to as a ring electrode because it may wholly circumscribe longitudinal sidewall 17. Distal end 26 is referred to as ‘‘distal” in that it is expected to be the leading end as IMD 14 is advanced through a delivery tool, such as a catheter, and placed against a targeted implant site.

[0052] Electrodes 16 and 18 form a cathode and anode pair for bipolar cardiac pacing and sensing. In other examples, IMD 14 may include two or more ring electrodes, two tip electrodes, and/or other types of electrodes exposed along pacemaker housing 15 for delivering electrical stimulation to the patient’s heart and sensing cardiac electrical signals. Electrodes 16 and 18 may be, w ithout limitation, titanium, platinum, iridium or alloys thereof and may include a low polarizing coating, such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, among others. Electrodes 16 and 18 may be positioned at locations along IMD housing 15 other than the locations shown.

[0053] Housing 15 can be formed from a biocompatible material, such as a stainless steel or titanium alloy. In some examples, housing 15 may include an insulating coating. Examples of insulating coatings include parylene, urethane, PEEK, or poly imide, among others. The entirety of the housing 15 may be insulated, with only electrodes 16 and 18 left uninsulated. Electrode 16 may serve as a cathode electrode and be coupled to internal circuitry, e.g., a pacing pulse generator and cardiac electrical signal sensing circuitry enclosed by housing 15, via an electrical feedthrough crossing housing 15. Electrode 18 may be formed as a conductive portion of housing 15 defining a ring electrode that is electrically isolated from the other portions of the housing 15 as generally shown in FIG. 2. In other examples, the entire periphery of the housing 15 may function as an electrode that is electrically isolated from tip electrode 16, instead of providing a localized ring electrode such as electrode 18.

[0054] An accelerometer 212 is included in IMD 14 for sensing an acceleration signal responsive to acceleration forces imparted on IMD 14. Accelerometer 212 is shown as a 3D accelerometer having a sensor element 40, 42 and 44, e.g., a piezoelectric element or microelectro-mechanical system (MEMS) device aligned along each one of three orthogonal axes Al, A2 and A3 of accelerometer 212. Each sensor element 40, 42 and 44 can sense acceleration that is transduced into an electrical signal, e.g., by converting the acceleration to a force or displacement that is converted to the electrical signal, referred to herein as an “axis signal.” For instance, a sensor element of a MEMS device may produce an electrical signal correlated to changes in capacitance that occurs with deflection of a mass of the sensor element along a given axis of the accelerometer. Each axis signal represents the acceleration force component acting on IMD 14 and accelerometer 212 along the respective axis Al, A2 or A3. The axis signal may vary as IMD 14 is subjected to acceleration forces due to changing orientation of IMD 14 relative to gravity as well as other acceleration forces, such as cardiac motion, patient body motion, or other external acceleration forces, etc.

[0055] In some examples, one accelerometer sensor element 42 may be aligned with the longitudinal axis 22 of IMD 14, as indicated by sensor axis A2. The second and third accelerometer sensor elements 40 and 44 may be aligned in radial directions relative to the IMD longitudinal axis 22 and sensor axis A2, as represented by radial axes Al and A3, respectively. In this way, sensor 212 may produce a three-dimensional accelerometer signal having three orthogonal axis signals produced by the respective accelerometer sensor elements 40, 42 and 44. As the orientation of IMD 14 changes with respect to gravity (G) 23, the DC or average acceleration signal produced by each sensor element 40, 42 and 44 will vary. The three dimensional acceleration vector defined by the average or DC components of the three axis signals is expected to be equal to gravity, e g., within a calibration tolerance. The three axis signals can be analyzed according to the techniques disclosed herein to determine the pitch and roll of IMD 14 relative to earth center for use in determining the dynamically changing position of IMD 14, which may be rendered into a graphical, moving display of the IMD position relative to earth center, e.g., for display on display unit 54 of external device 50 (shown in FIG. 1).

[0056] IMD 14 may include a set of fixation tines 36 or other fixation member(s) to secure IMD 14 to patient tissue at the implant site. Fixation tines 36 are configured to anchor IMD 14 to position electrode 16 in operative proximity to a targeted tissue for delivering therapeutic electrical stimulation pulses. Numerous types of active and/or passive fixation members may be employed for anchoring or stabilizing IMD 14 in an implant position. IMD 14 may include a set of fixation tines as generally disclosed in commonly-assigned U.S. Patent No. 10,835,737 (Grubac, et al.), incorporated herein by reference in its entirety. In other examples, as described below in conjunction with FIG. 4, IMD 14 may be provided with an electrode 24 extending from distal end 26 in the shape of a tissue piercing helix, instead of (or in addition to) the button type of electrode as shown in FIG. 2. A helical electrode may provide fixation of IMD 14 at the implant site and serve as an electrode for sensing and pacing, for example, without requiring fixation tines.

[0057] IMD 14 may include a delivery tool interface 38. Deliver}' tool interface 38 may be located at the proximal end 28 of IMD 14 and is configured to connect to a delivery tool used to position IMD 14 at an implant location during an implantation procedure, for example within a heart chamber. A clinician may rotate, advance and/or retract IMD 14 using the delivery tool connected to IMD 14 via the delivery tool interface 38.

[0058] FIG. 3 is a diagram 100 of a delivery tool 102 loaded with IMD 14 of FIG. 2 prior to deployment of IMD 14 at an implant site. Delivery tool 102 may include an elongated tubular body 105 extending between a proximal handle 108 and distal receptacle 103 terminating at delivery tool distal end 104. Delivery tool 102 may be a steerable tubular device or be configured to traverse a guidewire to facilitate navigation and advancement of delivery tool distal end 104 to a target implant site. In any case, delivery tool 102 may be directed within a patient’s body, such as through a vascular structure or along a navigation pathway (e.g., extending subcutaneously, submuscularly, sub-stemally, intra-abdominally, trans-thoracically etc.), to a target implant site to enable remote positioning and deployment of IMD 14.

[0059] Distal receptacle 103 is sized to receive IMD 14. For example, receptacle 103 may have an inner diameter that is greater than or about the same size as, e.g., slightly greater than, the outer diameter of IMD 14 in order to receive IMD 14 and retain IMD 14 within receptacle 103 during advancement of the distal end 104 of delivery tool 102 to an implant site. When IMD 14 is positioned within receptacle 103, the inner wall of receptacle 103 holds fixation tines 36 in a spring-loaded position as shown in FIG. 3. In this spring-loaded position, fixation tines 36 store enough potential energy to secure IMD 14 to a patient tissue upon deployment of IMD 14 from delivery tool 102. The fixation tines 36 may be deploy able from the relatively straightened, spring-loaded position (shown) when held within receptacle 103, in which distal tips 37 of the fixation tines 36 point generally distally away from IMD distal end 26. Upon deployment from (e.g., advancement out of) the delivery tool 102, the distal tips 37 of the fixation tines 36 may penetrate adjacent tissue and relax into the generally hooked position as shown in FIG. 2. The fixation tines 36 bend back towards the IMD housing 15 from the relatively straightened, spring- loaded position shown in FIG. 3 to the curved or hooked position shown in FIG. 2. thereby engaging with and entrapping body tissue 101 at the implant site within the curved or hooked portion of the fixation tines 36.

[0060] Delivery tool distal end 104 defines a distal aperture 106 through which IMD 14 may be loaded into the tubular receptacle 103 prior to advancement of distal end 104 to an implant site. Upon reaching the implant site and establishing contact with body tissue 101, IMD 14 may be advanced forw ard out of aperture 106. A deployment member 110 of deliver}' tool 102 can be positioned against the proximal end 28 of IMD 14, e.g., cupped over delivery tool interface 38 shown in FIG. 2. Deployment member 110 can be advanced by a clinician by pressing against the proximal plunger 112 of deliver}' tool handle 108 to push IMD 14 toward aperture 106 to deploy fixation tines 36. Proximal plunger 112 can be provided at the proximal end of deployment member 110, which extends from the handle 108 through the hollow deliver}' tool body 105. The distal tips 37 of fixation tines 36 pierce into the body tissue 101 (as IMD 14 is advanced toward and out of aperture 106), and fixation tines 36 move from the spring-loaded position as shown in FIG. 3 to the hooked position as shown in FIG. 2. The potential energy released by fixation tines 36 is sufficient to penetrate the body tissue 101 to capture body tissue 101 in the curved portion of each of the fixation tines 36 and secure IMD 14 to the body tissue 101.

[0061] In some examples, receptacle 103 may include other openings, e.g., vents 124, in addition to aperture 106 to provide an electrically conductive pathway through body fluid between electrode 16 and ring electrode 18. In this way, IMD 14 may be capable of performing electrical measurements while retained within receptacle 103. As described below, an impedance measurement and/or cardiac electrical signal may be sensed using electrodes 16 and 18 when IMD 14 is within the receptacle 103. A delivery tool configured to enable electrical signal sensing and measurements to be performed while retaining an IMD within the receptacle 103 is generally disclosed in U.S. Patent Application Publication No. 2021/0077022 (Grinberg, et al., filed September 10, 2020), the entire content of which is incorporated herein by reference.

[0062] Tether 120 may be attached to delivery tool interface 38 (not visible in FIG. 3 but shown in FIG. 2) of IMD 14. Tether 120 extends through the elongated body 105 of deliver)' tool 102. Following deployment of IMD 14, a clinician may remotely pull IMD 14 back into receptacle 103 by pulling on tether 120 at the proximal end of deliver)⁷ tool 102. Pulling IMD 14 back into receptacle 103 returns fixation tines 36 to the spring-loaded position from the hooked position. The proximal ends of active fixation tines 36 remain fixed to the distal end 26 of IMD 14 as fixation tines 36 move from the spring-loaded position to the hooked position and vice-versa. Fixation tines 36 may be configured to facilitate releasing IMD 14 from patient tissue 101 without tearing the tissue when IMD 14 is pulled back into receptacle 103 by tether 120. A clinician may redeploy IMD 14 with deployment member 110 by operating plunger 212, e.g., after rotating or other repositioning of IMD 14.

[0063] Tether 120 and/or deployment member 110 may be provided having sufficient torsional rigidity to enable rotation of IMD 14 within receptacle 103. In this way, when tether 120 is coupled to deliver)' tool interface 38 and/or deployment member 110 is secured over delivery tool interface 38 on proximal end 28 of IMD 14, a user may rotate the proximal end of tether 120 and/or plunger 112 of deployment member 110 to rotate IMD 14 within receptacle 103 prior to deployment of IMD 14 from receptacle 103. In other examples, a user may rotate the proximal handle 108 of delivery tool 102 when elongated body 105 is provided with sufficient torsional stiffness to transfer torque applied to proximal handle 108 to receptacle 103. In this way, IMD 14 may be rotated by rotating receptacle 103 and IMD 14 together prior to deployment of IMD 14. [0064] Using proximal handle 108, a user may be able to rotate IMD 14 clockwise or counterclockwise, advance or retract IMD 14, and move and/or angulate IMD 14 laterally (e.g., left, right, up or dow n) with respect to the surface of body tissue 101 to position IMD 14 at the implant site against body tissue 101. As described below as the clinician rotates or otherwise modifies the position of IMD 14 prior to deployment, acceleration signals sensed by IMD 14 may be used to generate dynamic position data, e.g., the dynamically changing pitch and roll of IMD 14 relative to earth center, to present positional information of IMD 14 to a clinician. The positional information may be in the form of a graphical rendering of the IMD position moving in real time, e.g., during an implant procedure, as acceleration signals are received and analyzed. After delivery tool 102 is removed and IMD 14 is fixed at the implant site, acceleration signals sensed by IMD 14 may be analyzed for determining the position of IMD 14. Time-domain analysis of the positional data may enable a dynamic graphical rendering of motion of IMD 14, e.g., during a cardiac cycle. Time-domain analysis of the positional data may be used in assessing fixation of IMD 14 as further described below.

[0065] It is further contemplated that in some examples, delivery tool 102 may include an orientation sensor 140. Delivery tool 102 may include the orientation sensor 140. which may include at least a 3D accelerometer and in some examples a 3D magnetometer and/or 3D gyroscope, for sensing orientation signals for determining positional data of the delivery tool receptacle 103. The orientation sensor 140 may be carried by receptacle 103, for example at or near the delivery' tool distal end 104. The orientation sensor 140 may be coupled to electrical conductors extending through delivery tool elongated body 105 to delivery tool handle 108. [0066] Delivery tool handle 108 may include an interface and control unit 109 that can provide power to the orientation sensor 140, receive the orientation sensor signals, and transmit the orientation sensor signals, e.g., as raw signals or as filtered signals, to external device 50 (shown in FIG. 1). For instance, interface and control unit 109 may be capable of BLUETOOTH® or other wireless RF communication for transmitting the orientation sensor signals to external device 50 for processing and analysis according to the techniques disclosed herein.

[0067] In some examples, the interface and control unit 109 may be enabled to display qualitative positional data received from external device 50 by generating a visual user feedback signal (e.g., by light emitting diodes or a digital display), audible user feedback signal (e.g., as beeps or tones emitted by a speaker) and/or tactile user feedback signal (e.g.. as a vibration), to indicate to a user when the positional data, e.g., a pitch angle, is within a recommended range with respect to earth center for deploying IMD 14 at a particular anatomical site. The patient may be in a known position relative to gravity, e.g., supine, such that a recommended pitch angle range for IMD 14 and delivery tool catheter 103 may be defined for an expected IMD implant site. In some examples, the external device 50 may generate a graphic image of the delivery tool receptable 103 that is dynamically updated as positional data is updated based on analysis of the orientation sensor signal according to the techniques disclosed herein.

[0068] FIG. 4 is a diagram of a medical device system 10’ including IMD 14’ provided with a helical electrode 24 extending from distal end 26 of IMD 14’ instead of or in addition to the button type of electrode 16 of IMD 14 shown in FIG. 2. FIG. 5 is a diagram of IMD 14’ having helical electrode 24 extending from distal end 26. IMD 14’ may include IMD housing 15 as generally described above, e.g., having a generally cylindrical longitudinal side wall extending between distal end 26 and proximal end 28. IMD 14’ is provided with a different electrode arrangement and fixation member than IMD 14 shown in FIG. 2. [0069] In FIG. 4, IMD 14’ is shown implanted at a different implant site in the patient’s heart than in FIG. 1. In FIG. 4, IMD 14’ is implanted in the RA. IMD 14’ may be implanted in the RA for providing atrial sensing and pacing and/or ventricular sensing and pacing. For example, IMD 14’ may be advanced using a delivery tool to a location beneath the AV node and near the tricuspid valve annulus, generally in the Triangle of Koch, to advance electrode 24 toward the basal portion of the interventricular septum to deliver ventricular pacing and sense ventricular signals from a right atrial approach. Electrode 24 may be advanced into the interventricular septum 9 from an insertion point in the Triangle of Koch to position distal helical electrode 24 along or near the His bundle for delivering ventricular pacing pulses via the native conduction system, sometimes referred to as the His-Purkinje system.

[0070] Distal helical electrode 24 as shown in FIGs. 4 and 5 can serve as an electrode and as a fixation member for anchoring IMD 14’ at the implant site in the RA (or other locations). For example, helical electrode 24 may be paired with the proximal ring electrode 18 in a bipolar electrode pair for delivering ventricular pacing and for sensing ventricular cardiac signals, e.g., R-waves. In some examples, IMD 14’ may include more than two electrodes. For instance, a second ring electrode 20 shown circumscribing a distal portion of the longitudinal sidew all 17 of housing 15 can be provided. The distal ring electrode 20 may be provided for sensing atrial signals, e.g., P-waves (and in some instances far field R-waves) and delivering atrial pacing pulses in a bipolar atrial pacing electrode vector including distal ring electrode 20 paired with proximal ring electrode 18.

[0071] Additionally or alternatively, IMD 14’ may include distal electrode 16, e.g., as a button electrode, on distal end 26 of IMD 14’ in addition to the distal helical electrode 24. One or more button, ring, segmented ring or other types of electrodes may be carried by IMD 14’ on its distal face at distal end 26. In some examples, the distal button electrode 16 and distal helical electrode 24 may be used for performing electrical measurements during an implant procedure for detecting contact of helical electrode 24 with tissue at an implant site as further described below. [0072] As described above, IMD 14 may be configured to communicate wirelessly with external device 50. Acceleration signals sensed by IMD 14’ and/or data derived therefrom may be transmitted from IMD 14’ to external device 50 for displaying dynamic positional data, which may include a graphical rendering of a moving graphic image of IMD 14’ relative to earth center. While a delivery tool is not shown in FIGs. 1 and 4, it is to be understood that acceleration signals and/or data derived therefrom may be transmitted to external device 50 from IMD 14/14’ while retained by a delivery tool, e.g., as shown in FIGs. 2 and 6, as IMD 14/14’ is being advanced to an implant site and deployed from the delivery tool, e.g.. before and/or after being anchored at the implant site.

[0073] FIG. 6 is a diagram of IMD 14’, provided with distal helical electrode 24, loaded in a deliver^' tool 102 prior to deployment at an implant site. In this example, delivery' tool 102 includes tether 120 having a distal clamp 134 configured with opposing teeth 136 configured to grasp delivery tool interface 38 of IMD 14’. Both tether 120 and deployment member 110 may extend from the proximal handle 108 of delivery tool 102 through the lumen of delivery tool elongated body 105 to the delivery' tool receptacle 103. Tether 120 may be configured to be longitudinally and rotationally moveable within a lumen of deployment member 110 so that, by manipulating the proximal end of tether 120 extending from proximal handle 108, a user may advance, retract and rotate IMD 14’. The teeth 136 of clamp 134 may open when extended out of the distal end of deployment member 110 (e.g., within receptacle 103) and actuated to close down on delivery' tool interface 38 of IMD 14’, e.g., when within the distal end of deployment member 110. Clamp 134 may be actuated (e.g., opened or closed) under the control of a clinician operating delivery tool 102. For example, a clinician may actuate clamp 134 open or closed from a control mechanism of deliver}' tool 102, e.g., on or adjacent proximal handle 108. Clamp 134 is shown in a position that is not in engagement with delivery tool interface 38 in FIG. 6 for the sake of clarity. It is to be understood, however, that clamp 134 may engage IMD 14’. e.g., clamp onto or around delivery tool interface 38, until IMD 14’ is securely fixed at the target implant site. Upon fixation at the target implant site, clamp 134 may be opened, e.g., by retracting deployment member 110 to allow' clamp 134 to open or using an actuation member on the proximal handle 108 to release delivery tool interface 38 from clamp 134. Deployment member 110 and tether 120 may be retracted proximally within receptacle 103 and elongated body 105. Delivery tool 102 may then be withdrawn from the patient leaving IMD 14’ securely fixed at the target implant site.

[0074] Tether 120 may be configured to provide torsional transfer from the proximal handle 108 to clamp 134. Clamp 134 may be closed around delivery tool interface 38 such that rotation of tether 120 causes rotation of IMD 14’. Rotation of IMD 14’ enables advancement and retraction of helical electrode 24 into and back out of body tissue. As helical electrode 24 is rotated into body tissue 101 via rotation of IMD 14’, IMD 14’ may advance out of aperture 106 to deploy IMD 14’ from receptacle 103.

[0075] According to the techniques disclosed herein, the roll and pitch of IMD 14’ can be determined during an implant procedure from acceleration signals sensed by IMD 14’. A total number of turns performed for advancing electrode 26 into the body tissue 101 may be determined based on the cumulative changes in determined roll over time. A user feedback signal may be generated to notify the user when a minimum and/or maximum number of turns is reached to achieve reliable fixation without over advancement. Additionally or alternatively, an indication of acceptable pitch or unacceptable pitch for reliable fixation of IMD 14’at a particular implant site may be generated for display by external display unit 54 of external device 50. A graphical rendering of the IMD position in real time, during rotation and positioning of IMD 14’ at an implant site, may be generated and displayed by external device 50 without requiring other imaging methods for the clinician to visualize the position of IMD 14. [0076] IMD 14’ may be configured to sense electrical signals and/or perform electrical measurements, e.g., sense a cardiac electrical signal, deliver a pacing pulse for determining cardiac pacing capture, and/or perform an electrical impedance measurement. To facilitate such measurements, delivery tool receptacle 103 may include one or more vents 124 extending through the sidewall of receptacle 103 to provide an electrically conductive pathway to ring electrode 18 of IMD 14’ when IMD 14’ is retained within receptacle 103. In some examples, one or more vents 124 are provided at a location that is approximately aligned with ring electrode 18 along the longitudinal length of receptacle 103 when IMD 14 is retracted within receptacle 103. In some examples, a single vent 124 may be provided. In other examples, multiple vents 124 may be spaced apart circumferentially and/or longitudinally along receptacle 103. For example, two vents 124 may be on opposing sides of receptacle 103. In other examples, three, four or more vents may be provided, spaced apart circumferentially and/or longitudinally along receptacle 103.

[0077] Vents 124 may provide a fluid pathway for blood through receptacle 103. By providing a fluid pathway, e.g.. for blood flowing in a heart chamber, an electrically conductive pathway exists between an electrode 18 within receptacle 103 and distal electrode 24 for performing electrical measurements and sensing electrical signals. In some examples, the fluid pathway extending through one or more vents 124 provides an electrically conductive pathway between tip electrode 16 and ring electrode 18 carried by IMD 14 for enabling sensing of cardiac signals via IMD housing-based electrodes 16 and 18 while IMD 14 is retained within receptacle 110. [0078] FIG. 7 is a diagram 200 of an example configuration of an IMD of a medical device system configured to perform the techniques disclosed herein according to some examples. FIG. 7 is described with reference to IMD 14 shown in FIG. 1 for the sake of illustration and may also generally correspond to IMD 14’ shown in FIG. 5. IMD 14 may include a pulse generator 202. a cardiac electrical signal sensing circuit 204, a control circuit 206, memory 210, communication circuit 208, accelerometer 212 and a power source 214. The various circuits represented in FIG. 7 may be combined on one or more integrated circuit boards, which may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, state machine or other suitable components that provide the described functionality. [0079] Accelerometer 212 is a three-dimensional sensor, with each axis sensing an axis signal that may be analyzed individually or in combination for detecting a position of accelerometer 212 (and thus IMD 14) relative to gravity. Based on the amplitude of each Al, A2 and A3 axis signal of accelerometer 212, control circuit 206 and/or other processing circuitry⁷ of the medical device system (e.g., external device processor 52) may determine the pitch and roll of IMD 14 relative to earth center to generate dynamic positional data that can be used to provide IMD implantation guidance and/or to assess the IMD position post-implant, e.g., to assess fixation of IMD 14. The dynamic positional data may be generated in real time or in post-processing methods as further described below.

[0080] Accelerometer 212 can produce an electrical signal correlated to motion or vibration of sensor 212 (and IMD 14), e.g., when subjected to acceleration forces of flowing blood, cardiac motion, and patient body motion as well as the DC or averaged components relative to gravity⁷. As such, in some examples, control circuit 206 may detect cardiac motion signals, patient physical activity metrics, or other motion related events or metrics using the acceleration signals received from accelerometer 212. In other examples, a second accelerometer or other motion sensor may⁷ be provided for sensing motion, such as patient body motion associated with physical activity and/or cardiac motion.

[0081] Accelerometer 212 is shown included in an orientation sensor 240, which may include one or more analog-to-digital converter (ADC) 216. filter/amplifier 218, rectifier, and/or other components for producing an acceleration signal that is passed to control circuit 206. Each axis signal produced by each individual axis of the 3D accelerometer 212 may be filtered by a low⁷ pass filter included in filter/amplifier 218, e.g., a 0.5 or 1 Hz low pass filter, for providing a DC or averaged axis signal to control circuit 206. The low pass filtered signal sensed by each sensor element 40, 42 and 44 may be analyzed for determining the pitch and roll of IMD 14. In some examples, one or more high pass or band pass filtered acceleration signals may⁷ be digitized by⁷ an ADC and optionally rectified for use by control circuit 206 for detecting cardiac event signals and/or determining a patient physical activity metric, which may be used for controlling the timing and rate of cardiac pacing pulses.

[0082] The general arrangement of the block diagram of orientation sensor 240 including accelerometer 212, ADC 216 and filter/amplifier 218 is shown for the sake of example w⁷ith no limitations intended. For example, a pre-filter and/or amplifier may be provided for receiving the signals from each sensor element 40, 42 and 44 and passing the filtered and/or amplified signals to ADC 216. Low-pass and/or bandpass filtering of the axis signals may be applied prior to and/or after digitization by ADC 216. ADC 216 may digitize each of the axis signals and apply a respective bias and sensitivity to each of the digitized axis signal according to an accelerometer calibration, e.g., using gravity as a reference vector. A bias and sensitivity for each axis signal may be stored in IMD memory 210 for use by ADC 216 in passing a calibrated digital signal to control circuit 206. Furthermore, it is recognized that filtering, averaging, amplification and/or other signal processing of the orientation sensor signals may be performed by control circuit 206 or by external device 50 such that the raw orientation sensor signal may be passed to control circuit 206 and/or transmitted to external device 50 for processing and analysis.

[0083] In some examples, orientation sensor 240 may include a secondary sensor 242 for enabling determination of the position of IMD 14 relative to a vertical axis parallel to gravity. The rotation of IMD 14 around a vertical axis parallel to gravity, referred to herein as the "yaw angle,” may be undetermined from the three accelerometer axis signals because the three accelerometer axis signals may be the same at any 360 degree rotation of the IMD 14 in a horizontal plane perpendicular to gravity'. In some examples, the secondary sensor 242 may be included in orientation sensor 240 and may include a gyroscope or magnetometer for sensing orientation signals that vary relative to a reference vector that can be orthogonal to gravity. For example, a reference magnetic field vector or a reference angular velocity vector may extend in the horizontal plane perpendicular to gravity’. The secondary' sensor signals may vary with rotation of IMD 14 around a vertical axis that is parallel to gravity as the orientation of IMD 14 changes with respect to a reference vector for the secondary sensor 242 that is orthogonal to gravity. As further described below, processing circuitry of the medical device system may determine a yaw angle of IMD 14 as the angle of rotation in a horizontal plane around a vertical axis (parallel to gravity) using the output of the secondary sensor. The yaw angle may be determined in addition to determining the pitch and/or roll angles from the 3D accelerometer signal.

[0084] The secondary sensor 242 may be a 3D magnetometer or a 3D gyroscope in some examples. In some cases, orientation sensor 240 may include or be provided as an inertial measurement unit (IMU) that combines a 3-axis accelerometer and a 3-axis gyroscope, a 3-axis accelerometer and a 3-axis magnetometer, or a 3-axis accelerometer, a 3-axis gyroscope and a 3- axis magnetometer. In this way, the pitch, roll and yaw of IMD 14 may be determined from the orientation sensor signals sampled at a series of time points for rendering a dynamically -moving graphic image of IMD 14 in three dimensions by external device display unit 54.

[0085] Communication circuit 208 includes a transceiver 209 and antenna 211 for transmitting and receiving data, e.g., via a radio frequency (RF) communication link with another device, e.g., external device 50 as generally described above in conjunction with FIG. 1 and in some cases with another IMD co-implanted with IMD 14. Acceleration signals and/or data derived therefrom may be transmitted by communication circuit 208 to external device 50 for analysis for determining IMD positional data in some examples. In other examples, control circuit 206 may determine the IMD positional data, e.g., the pitch and roll of IMD 14 and yaw if determined, and transfer the position data to external device 50 via communication circuit 208. Additionally, programmable control parameters and algorithms for performing and controlling cardiac signal sensing, cardiac pacing and other functions of IMD 14 may be transmitted to IMD 14 and received by IMD 14 via communication circuit 208 and stored in memory 210 for access by control circuit 206.

[0086] IMD 14 may include a sensing circuit 204 configured to receive a cardiac electrical signal via electrodes 16 and 18 by a pre-filter and amplifier circuit 220. Pre-filter and amplifier circuit may include a high pass filter to remove DC offset, e.g., a 2.5 to 5 Hz high pass filter, or a wideband filter having a passband of 2.5 Hz to 100 Hz to remove DC offset and high frequency noise. Pre-filter and amplifier circuit 220 may further include an amplifier to amplify the "raw" cardiac electrical signal passed to analog-to-digital converter (ADC) 226. ADC 226 may pass a multi-bit, digital electrogram (EGM) signal to control circuit 206 for use by processor 244 in identifying ventricular electrical events (e.g., R-waves or T-waves) and/or atrial electrical events, e.g., P-waves. Identification of cardiac electrical events may be used for identifying cardiac cycles, determining a heart rhythm and controlling electrical stimulation therapies delivered by pulse generator 202.

[0087] Sensing circuit 204 may include a cardiac event detector circuit 224 for sensing cardiac event signals attendant to cardiac electrical depolarizations, e g., P-waves attendant to atrial depolarizations and/or R-waves attendant to ventricular depolarizations. Cardiac event detector circuit 224 may include a sense amplifier or other detection circuitry that compares the incoming rectified, cardiac electrical signal to a cardiac event sensing threshold, e.g., an R-wave sensing threshold or a P-wave sensing threshold, which may be an auto-adjusting threshold. When the incoming signal from rectifier/amplifier circuit 222 crosses the cardiac event sensing threshold, the detector circuit 224 may produce a sensed event signal (e.g., a Vsense signal when the R- wave sensing threshold is crossed or an Asense signal when the P-wave sensing threshold is crossed). The sensed event signal can be passed to control circuit 206 for use in controlling cardiac pacing pulses or other electrical stimulation therapies delivered by pulse generator 202, determining the heart rate and rhythm, and for identifying cardiac cycles for use in determining IMD positional data over a cardiac cycle. Cardiac event detector circuit 224 or control circuit 206 may receive the digital output of ADC 226 for detecting R-waves and/or P-waves by a comparator, morphological signal analysis of the digital EGM signal or other cardiac event signal detection techniques. Control circuit 206 may provide sensing control signals to sensing circuit 204, e.g., cardiac event sensing threshold parameters, sensitivity⁷, and various blanking and refractory intervals applied to the cardiac electrical signal for controlling cardiac event signal sensing.

[0088] Control circuit 206 may include a pace timing circuit 242 and a processor 244. In addition to receiving acceleration signals from accelerometer 212 for determining IMD positional data, processor 244 may receive acceleration signals from accelerometer 212 for detecting cardiac mechanical events in some examples. For instance, an accelerometer signal received as a single axis signal or a combination of two or more axis signals from accelerometer 212 may be analyzed by processor 244 for detecting an acceleration signal waveform attendant to cardiac mechanical events, e.g., ventricular systole and/or atrial systole. In some examples, processor 244 may sense atrial systolic events from an acceleration signal when IMD 14 is implanted in the RV for triggering an atrial synchronous ventricular pacing pulse. Processor 244 may additionally or alternatively determine a patient activity metric from an acceleration signal received from accelerometer 212 for determining a sensor indicated pacing rate (SIR) to control pulse generator 202 to deliver rate response pacing in accordance with the patient’s physical activity level and metabolic need.

[0089] Pace timing circuit 242 may include one or more timers or counters for controlling various pacing escape interval. For example, pace timing circuit 242 may include a lower pacing rate interval timer for controlling pulse generator 202 to deliver pacing pulses according to a minimum pacing rate. When an atrial P-wave is sensed by sensing circuit 204 or an atrial systolic event is detected from the acceleration signal received from sensor 212, triggering a ventricular pacing pulse, pace timing circuit 242 may start an AV pacing interval to control pulse generator 202 to deliver an atrial synchronous ventricular pacing pulse upon expiration of the AV pacing interval.

[0090] Pulse generator 202 generates electrical pacing pulses that are delivered to the patient’s heart, via electrodes 16 and 18. As described above, additional electrodes may be provided in some examples to enable IMD 14 to deliver atrial and ventricular pacing pulses. In addition to providing control signals to pace timing circuit 242 and pulse generator 202 for controlling the timing of pacing pulses, processor 244 may retrieve programmable pacing control parameters from memory 210, such as pacing pulse amplitude and pacing pulse width, which are passed to pulse generator 202 for controlling pacing pulse delivery⁷.

[0091] Pulse generator 202 may include charging circuit 230. switching circuit 232 and an output circuit 234. Charging circuit 230 may include a holding capacitor that may be charged to a pacing pulse amplitude by a multiple of the battery voltage signal of power source 214 under the control of a voltage regulator. The pacing pulse amplitude may be set based on a control signal from control circuit 206. Switching circuit 232 may control when the holding capacitor of charging circuit 230 is coupled to the output circuit 234 for delivering the pacing pulse. For example, switching circuit 232 may include a switch that is activated by a timing signal received from pace timing circuit 242 upon expiration of an AV pacing interval or a low er rate pacing interv al and kept closed for a programmed pacing pulse width to enable discharging of the holding capacitor of charging circuit 230. The holding capacitor, previously charged to the pacing pulse voltage amplitude, is discharged across electrodes 16 and 18 through the output capacitor of output circuit 234 for the programmed pacing pulse duration.

[0092] Control circuit 206 may be configured to perform an impedance measurement by controlling pulse generator 202 to deliver a drive signal, which may be a constant current or constant voltage signal, delivered to an electrode pair, e.g., electrodes 16 and 18 or electrodes 24 and 16 (of IMD 14’ shown in FIG. 5). A resulting voltage or current signal may be measured between a selected recording pair of electrodes by sensing circuit 204 and passed to control circuit 206 for determining an impedance measurement. The impedance measurement may be used by control circuit 206 for determining electrode impedance for detecting tissue contact when IMD 14 is moved to a position against cardiac tissue. The impedance measurement is expected to be very' low when distal electrodes 16 and 24 are in the blood pool in a heart chamber and increase when the electrode is in contact with cardiac tissue.

[0093] Memory 210 may include computer- readable instructions that, when executed by control circuit 206, cause control circuit 206 to perform various functions attributed throughout this disclosure to IMD 14. The computer-readable instructions may be encoded within memory' 210. Memory' 210 may include any non-transitory, computer-readable storage media including any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory’ (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or other digital media with the sole exception being a transitory' propagating signal. Memory' 210 may store data used by control circuit 206 to perform various functions attributed to IMD 14 herein. For example, memory 210 may store calibration values for the bias and sensitivity for each of the axis signals of accelerometer 212 and algorithms for determining the pitch and roll of IMD 14 based on the accelerometer axis signals.

[0094] Power source 214 provides power to each of the other circuits and components of IMD 14 as required. Power source 214 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The connections between power source 214 and other pacemaker circuits and components are not shown in FIG. 7 for the sake of clarity⁷ but are to be understood from the general block diagram of FIG. 7. For example, power source 214 may provide power as needed to charging and switching circuitry included in pulse generator 202, amplifiers, ADC 226 and other components of sensing circuit 204, communication circuit 208 and accelerometer 212.

[0095] The functions attributed to IMD 14 and other IMDs described herein may be embodied as one or more processors, controllers, hardware, firmware, software, or any combination thereof. Depiction of different features as specific circuitry⁷ is intended to highlight different functional aspects and does not necessarily^ imply that such functions must be realized by separate hardw are, firmware or software components or by any particular circuit architecture. Rather, functionality associated with one or more circuits described herein may be performed by separate hardware, firmware or software components, or integrated within common hardware, firmware or software components. Providing software, hardware, and/or firmware to accomplish the described functionality⁷ in the context of any modem medical device system, given the disclosure herein, is within the abilities of one of skill in the art.

[0096] While one example IMD 14 is described with reference to FIG. 7. it is recognized that a variety of IMDs may include an accelerometer sensing acceleration signals in three dimensions. The IMD having a 3D accelerometer 212 can be included in a medical device system configured to perform the techniques disclosed herein for determining IMD positional data for generating a dynamic image of the IMD, e.g.. in a graphical user interface, and/or assessing its fixation at an implant site. An IMD included in a medical device system configured to perform the techniques disclosed herein is therefore not limited to being a cardiac pacemaker and may be any of the example IMDs listed herein, with no limitation intended.

[0097] FIG. 8 is a flow chart 300 of a method that may be performed by a medical device system for determining dynamic IMD positional data according to some examples. For the sake of illustration, the process of flow chart 300 is described primarily with reference to IMD 14’ of FIGs. 4 — 6 in communication with the external device 50 as shown in FIG. 4. It is to be understood, however, that the process of flow chart 300 can be performed in conjunction with IMD 14 as well as other IMDs for determining positional information and presenting and displaying positional information in a GUI.

[0098] With continued reference to FIGs. 4 and 7, external device 50 may generate a graphic image of IMD 14" in a starting position in a GUI displayed by display unit 54 at block 301. The starting position may be any nominal position defined by a starting roll and starting pitch relative to a local coordinate system. For example, a nominal starting position displayed by display unit 54 may be IMD 14’ positioned with its longitudinal axis 22 in the horizontal plane relative to gravity as further described below in conjunction with FIG. 9A. The longitudinal axis 22 and the A2 axis of accelerometer 212 may extend parallel to a y-axis of a local coordinate system in the displayed starting position of IMD 14’. The Al and A3 axes of accelerometer 212 may be parallel with the z-axis and the x-axis, respectively, of the local coordinate system. In this starting position, the roll angle around the A2 axis may be defined as 0 degree roll, and the pitch angle around the x-axis may be defined as 0 degree pitch or 90 degree pitch, as examples, in accordance with a selected convention as further described below.

[0099] At block 302 of FIG. 8, external device processor 52 may receive accelerometer axis signals from IMD 14’. IMD 14’ may transmit each axis signal to external device 50 via IMD communication circuit 208 as each axis signal is received from accelerometer 212. Control circuit 206 may determine the amplitude of each axis signal, e.g.. according to a desired sampling rate, and transmit the amplitudes of each axis signal to external device 50 in real time, neglecting any processing delays. While real time analysis of the axis signals may be performed for generating a dynamically moving graphical image of IMD 14’ in a GUI in real time, it is to be understood that the axis signal data and/or positional data derived therefrom may be stored for generating images of the IMD 14’ position for review by a clinician at a later time, e.g., at a time after accelerometer signal acquisition.

[0100] The lowpass filtered axis signal amplitudes received from accelerometer 212 may be normalized and/or calibrated to provide a projection of the force of gravity along the respective Al, A2 and A3 axis resulting in a unit vector equal to -1 g (within a calibration tolerance) or a specified number of ADC units equivalent to -1 g (within a calibration tolerance). In the example described here, pitch and roll are determined using the amplitudes of the three axis signals, as further described below. Yaw being defined as rotation in the plane defined by the x-axis and y- axis of the local coordinate system, extending in the horizontal plane perpendicular to gravity (as shown in FIGs. 9A and 9B described below) may not be determined in some examples because rotation about the vertical z-axis in the horizontal x-y plane does not result in a change in the lowpass filtered accelerometer axis signals. The IMD 14’ may be rotated about the z-axis in any direction with no change in angulation relative to the x-y plane and the Al, A2 and A3 axis signals will each measure the same gravitational component. As such, dynamically determined positional data derived from the accelerometer signals may include pitch and roll in some examples without a determination of yaw.

[0101] At block 304, external device processor 52 may determine the pitch at a sample time point t(i). The pitch (also referred to here as the "‘pitch angle”) may be determined as the angle of rotation around the A3 axis, extending parallel to the x-axis of the local coordinate system in the starting nominal position of IMD 14’. As further described below in conjunction with FIGs. 9 A and 9B, external device processor 52 may determine the pitch of IMD 14’ using the A2 axis signal amplitude. External device processor 52 may compute the pitch of IMD 14’ as the inverse cosine (arccos) of the ratio of the lowpass filtered amplitude “a” of the A2 axis signal at t(i) to gravity (pitch angle = arccos a(A2)/(lg). The pitch angle may reflect a clockwise rotation about the A3 axis of accelerometer 212, e.g.. toward gravity from the starting position in the horizontal plane.

[0102] At block 306, external device processor 52 may determine the roll at time t(i). The roll at time t(i), as described further below in conjunction with FIGs. lOA and 10B, can be determined by computing the inverse tangent (arctan) of the ratio of the amplitude of the Al axis signal, a(Al), to the amplitude of the A3 axis signal, a(A3), at time t(i). The roll may be computed as the angle of rotation about the A2 axis of the accelerometer 212.

[0103] At block 310, external device processor 52 can compute a directional difference in both pitch and roll from the most recent previous time point t(i-l) to the current time point t(i). The directional difference, e.g.. represented by the sign of the angular position at t(i-l) minus the angular position at t(i), can be used by the processing circuitry and display unit 54 in dynamically adjusting the angular position change in the correct direction of rotation of the image of IMD 14’.

[0104] At block 312, external device processor 52 generates an output to display unit 54 to adjust the image of IMD 14’ relative to the local coordinate system according to the determined pitch angle and roll angle and the direction of change (e.g., increased or decreased) from time t(i- 1) to t(i). The pitch angle may be increased or decreased based on the difference between the pitch determined at t(i-l) and t(i). For example, if the change from t(i-l) to t(i) is negative (increased pitch angle at cunent time point compared to previous time point), the image of IMD 14’ may be rotated to the determined t(i) pitch angle in a positive (e.g., clockwise) direction relative to the x-axis (and the A3 axis of the accelerometer 212). If the difference in pitch from t(i-l) to t(i) is positive (i.e., t(i) pitch angle is smaller than the t(i-l) pitch angle), the image of IMD 14’ may be rotated to the currently determined t(i) pitch angle in a negative (e.g., counterclockwise) direction relative to the x-axis (and the A3 axis of the accelerometer 212). [0105] The roll angle may be adjusted from the roll angle determined at t(i-l) to the roll angle determined at t(i) at block 312. The direction of the rotation of the IMD image relative to the y- axis (and the A2 axis of the accelerometer) from the currently displayed IMD position to the new roll angle at t(i) is based on the sign of the difference between the roll determined at t(i-l) and t(i). For example, if the change from t(i-l) to t(i) is negative (increased roll angle at the current time point compared to the previous time point), the image of IMD 14' may be rotated in a positive (e.g., clockwise) direction relative to the y-axis (and the A2 axis of the accelerometer 212). If the change in roll from t(i-l) to t(i) is positive (decreased roll angle at the current time point compared to the previous time point), the image of IMD 14’ may be rotated in a negative (e.g., counterclockwise) direction relative to the y-axis (and the A2 axis of the accelerometer 212) to the new roll angle determined at block 306.

[0106] After updating the displayed position of IMD 14’ at block 312 from the starting position, external device processor 52 may return to block 304 by advancing to the next sample time point (by increasing the value of the sample point (i) to (i+1) as indicated at block 314). External device processor 52 may compute the pitch and roll at the next time point using the sampled axis signal amplitudes as described above by repeating the process of blocks 304 and 306. The IMD image displayed in 3D in the GUI at block 312 may be adjusted dynamically according to the changes in pitch and roll determined at block 310 at each time point as the sampled axis signal amplitudes are received from IMD 14’. In this way the displayed image of IMD 14’, and optionally quantitative and/or qualitative positional information, may be updated at each sample time point to generate a dynamically moving graphic image of the position of IMD 14’ in real time. The dynamically moving image of IMD 14’ displayed by display unit 54 as the pitch and roll of the IMD 14’ is changing provides an implanting clinician, for example, with real time positional information without requiring medical imaging methods, such as fluoroscopy, which can increase radiation exposure to the patient and clinical staff.

[0107] In some examples, IMD memory 210 or external device memory 53 may store acceleration axis signal amplitudes and/or computed pitch and roll waveforms to be able to display the dynamic position of IMD 14’ at a later time rather than (or in addition to) in real time. For example, a pitch waveform may be generated by external device processor 52 by appending the pitch angle computed at each time point t(i) for a stored episode of acceleration axis signals. A roll waveform may be generated by external device processor 52 by appending the roll computed at each time point t(i) for the stored episode of acceleration axis signals. A moving image of IMD 14’ may be generated from the pitch and roll waveforms and displayed by display unit 54 for the episode of the recorded acceleration axis signals.

[0108] In some instances, a lapse in receiving the accelerometer axis signals or data derived therefrom by external device 50 could occur, e.g., due to a drop in the communication link between IMD 14’ and external device 50, data corruption, noise, etc. As such, one or more time points of computed pitch and roll angles may be missing. In other instances, the longitudinal axis 22 of IMD 14’ may become aligned with gravity such that the Al and A3 axis signals may be substantially zero (horizontal to gravity), making the pitch and roll angles undetermined for one or more time points. In these situations, external device processor 52 may interpolate pitch and roll angles between the most recently determined angles and a current time point when pitch and roll calculations can be resumed. In other examples, external device processor 52 may infer a direction of rotation from the most recently determined angles and a current time point. Without knowing the pitch and roll angles of intervening time points, the direction of rotation of the image of the IMD 14’ may be inferred. For example, if the roll angle has changed by 180 degrees (or less), external device processor 52 may infer the direction to be the same as the previously determined direction of rotation, even though the actual direction of rotation may be clockwise or counterclockwise.

[0109] While the examples presented herein primarily refer to external device processor 52 computing the pitch and roll, it is to be understood that control circuit 206 of IMD 14’ (or IMD 14) may compute the pitch and roll from the received accelerometer signal and transmit the computed values to external device 50 for use in generating the dynamically moving graphical image of IMD 14’ on display unit 54. The processing and analysis of orientation sensor signals for determining pitch and roll (and yaw as further described below) may be performed by processing circuitry of the IMD system by processing circuitry of a device of the IMD system, e.g., IMD 14’ or external device 50, or by processing circuitry of two or more devices in the medical devices system in a cooperative or distributed processing and analysis manner. [0110] FIG. 9A is a diagram 350 depicting an image of IMD 14’ in a nominal starting position according to some examples. FIG. 9B is a diagram 360 of an image of IMD 14’ after rotation of IMD 14’ to a determined pitch angle 362 about the x-axis of a local coordinate system. The images of IMD 14' represented in FIGs. 9A and 9B represent images displayed in a GUI of display unit 54 of external device 50. Images of IMD 14’ such as those represented in FIGs. 9A and 9B can be displayed as a dynamically moving image at each time point t(i), e.g., in real time, as the pitch and roll are computed at each time point t(i). In other examples, the images may be displayed in a stop action manner, e.g., with a new position determined and displayed as a still image that is updated at a specified update rate or upon a user entered command. In other examples, the graphical images of IMD 14’ such as those represented in FIGs. 9A and 9B and other examples presented herein may represent still images from a graphical moving display of IMD positions that may be frozen upon a user entered command.

[0111] In FIG. 9A, a default starting position of IMD 14’ may be displayed (as indicated at block 301 of FIG. 8). In this example, the longitudinal axis of IMD 14’, aligned with the A2 axis of accelerometer 212, is aligned with ay-axis of a local coordinate system. The Al axis of accelerometer 212 may be aligned with the z-axis of the local coordinate system, and the A3 axis of accelerometer 212 may be aligned with the x-axis of the local coordinate system. The distal end 26 of IMD 14’ may be positioned at the origin of the local coordinate system. The graphical image of IMD 14’ may be adjusted as IMD 14’ is being advanced to an implant site. Additionally or alternatively, the image of IMD 14' may be adjusted once IMD 14’ is at an implant site, e.g., with distal end 26 positioned against cardiac tissue at the implant site. The pitch and roll of IMD 14’ may be determined to adjust the pitch and roll of the graphical image of IMD 14’ while the distal end 26 remains relatively stationary at the implant site (though some minor lateral movement in any direction could occur prior to fixation of IMD 14’). The distal end 26 of the graphical image of IMD 14' may remain stationary at the origin of the local coordinate system. In instances when tissue contact is lost or the IMD is relocated to a new implant site, the IMD position may be reset to the nominal starting position so that the pitch and roll updates can be restarted beginning from the starting position. Other starting positions and other local coordinate systems may be defined relative to gravity.

[0112] In this example, the x-y plane corresponds to the horizontal plane perpendicular to gravity with the z-axis aligned with gravity. In the example shown in FIGs. 9A and 9B, a 3D rendering of the position of IMD 14’ may be displayed relative to the local coordinate axis. Quantitative angular positional information 354 may optionally be displayed by display unit 54 with the dynamically moving graphical image. For example, a display of the pitch angle and roll angle determined from the accelerometer axis signals at each time t(i) may dynamically change with the motion of the IMD image. The default starting position shown in FIG. 9A may be a pitch angle of 90 degrees (with zero degrees being defined when the distal end 26 is pointing straight down towards earth's center) and a roll angle of zero degrees. The pitch may vary from 0 degrees when distal end 26 is pointing straight down towards earth’s center (and proximal end 28 is pointing straight up) to 180 degrees when distal end 26 is pointing straight up, opposite gravity 352 (and proximal end 28 is pointing straight down). It is recognized that alternative conventions may be used for defining the angular ranges of pitch and roll (and yaw) from a minimum value to a maximum value of the angular range. For instance, instead of a range of 0 to 180 degrees as described here, the pitch angle range could be defined to extend from - 90 degrees when distal end 26 is pointing straight down to + 90 degrees when distal end 26 is pointing straight up (or vice versa). The roll may be used to count the number of 360 degree turns of IMD 14" around its longitudinal axis 22 (which is aligned with accelerometer axis A2 as previously shown in FIG. 5). As described below, when IMD 14’ makes tissue contact, the turn count may be initiated to be zero turns so that the number of turns of a distal helical electrode 24 (shown in FIG. 5) into the cardiac tissue can be counted.

[0113] The image of the IMD 14’ may be adjusted from the default starting position, e.g., after calculating the pitch and roll from the acceleration signals sensed at a subsequent sample time point as described above in conjunction with FIG. 8. As shown in the example of FIG. 9B, the position of IMD 14’ can be adjusted from the starting position (shown in FIG. 9A) to the pitch angle computed at a subsequent time point. The pitch angle 362 relative to the x-y plane has changed from 0 degrees (as shown in FIG. 9A) to angle 362 (as shown in FIG. 9B). If clockwise rotation with respect to the x-axis (in a direction toward gravity⁷ from the starting position of FIG. 9A) is defined as the positive directional change of the pitch angle, IMD 14’ is show n rotated to pitch angle of X degrees (90 degrees minus angle 362) by a negative or counterclockwise rotation from the starting position of 90 degrees shown in FIG. 9A, to the updated position shown in FIG. 9B. As shown in the diagram to the left in FIG. 9B, the cosine of angle 362 is equal to a(A2)/lg. As such, the external device processor 52 may compute the pitch angle 362 at time t(i) and rotate the image of IMD 14' relative to the x-axis to the pitch angle 362. The rotation may be in a counterclockwise or negative direction because the change in pitch angle from time zero to t(i) is negative. A user may observe the graphical image of IMD 14’ moving dynamically according to the directional difference between the two subsequent time points from the position of FIG. 9Ato the position of FIG. 9B. It is to be understood that multiple intermediate positions of IMD 14’ may be computed and displayed depending on the sampling rate and speed of updating the graphical image of IMD 14’.

[0114] As such, while the change in position from FIG. 9Ato FIG. 9B is shown at two discrete time points, it is to be understood that the image of IMD 14’ displayed by display unit 54 may be adjusted dynamically in real time as pitch and roll are determined from the acceleration axis signals to present real time motion of IMD 14’ as its position changes, which may be due to maneuvering of delivery tool 102 and/or cardiac motion, for example. In this way, a clinician can observe the position of IMD 14’ as IMD 14’ is advanced and maneuvered into an implant position, e.g., using delivery tool 102. In the example of FIG. 9B. IMD 14’ has not been rotated around its longitudinal axis, aligned with accelerometer axis A2, such that the roll has not changed from the starting position. Quantitative positional information 364 may display the pitch in degrees relative to the starting position and the roll as the number of turns around the longitudinal axis 22 counted from the starting position (in this case zero turns).

[0115] FIG. lOA is a diagram 370 depicting an image of IMD 14’ in a GUI in the same position as shown in FIG. 9B. IMD 14’ is rotated to a pitch angle 362 about the A3 axis, which is still aligned with the x-axis of the local coordinate system as in the starting position of FIG. 9A. In the position of FIG. 10A, no rotation about the IMD longitudinal axis 22. aligned with (or parallel to) accelerometer axis A2 has occurred.

[0116] FIG. 10B is a diagram 380 of an image of IMD 14’ after rotation of IMD 14’ around its longitudinal axis 22 (shown in FIG. 5) aligned with the accelerometer A2 axis. The graphical images of IMD 14’ represented in FIGs. 10A and 10B are images that may be displayed in a GUI of display unit 54 of external device 50. Images of IMD 14’ shown in FIGs. lOA and 10B can be displayed as still images for a given time point t(i), e.g., in a stop-action manner, or displayed as individual images of a series of images rendered in a dynamically moving graphical display of the motion of IMD 14’ generated from the determined IMD positions in real time or during postprocessing analysis.

[0117] In FIG. 10A. the roll of IMD 14’ is unchanged from a default starting position (as shown in FIG. 9A) and may be displayed as zero turns in the quantitative positional information 374. In FIG. 10B, IMD 14’ has been rotated about its longitudinal axis 22 (shown in FIG. 5, which is aligned with or parallel to the accelerometer A2 axis). As IMD 14’ is rotated about its longitudinal axis 22, the component of gravity 352 along the A2 axis is unchanged but the components of gravity 352 along the Al axis and the A3 axis of the IMD accelerometer 212 will change. The ratio of the amplitudes of the Al and A3 axis signals will vary as a tangential function of the angle of rotation about the A2 axis.

[0118] As such, using the Al axis signal amplitude. a(Al), and the A3 axis signal amplitude, a(A3), external device processor 52 can compute the angle 382 that IMD 14’ is rotated about its longitudinal axis 22 at a given time point t(i). External device processor 52 may compute the angle 382 as the inverse tangent (arctan) of the ratio of the amplitude of the Al axis signal to the amplitude of the A3 axis signal, as shown by the right-hand diagram in FIG. 10B.

[0119] External processor 52 can compare the roll angle 382 at a current time point t(i) and the most recent preceding time point t(i-l) to determine the directional difference in the change in roll angle. External processor 52 may generate an output to cause the display unit 54 to rotate the image of IMD 14’ clockwise or counterclockwise about the longitudinal axis 22 based on the sign of the difference in roll angles from the preceding time point to the current time point. For example, if the roll angle 382 has increased from the most recent preceding time point, the image of IMD 14' may be rotated clockwise to the new roll angle 382, e.g., between the A3 axis (or Al axis) and the y-z plane of the local coordinate system. If the roll angle 382 is decreased from a most recent preceding time point, the image of IMD 14’ may be adjusted to the roll angle 382 by rotating the image of IMD 14’ in a counterclockwise direction.

[0120] For the sake of clarity, a reference line 376 is show n in the images of FIGs. 10A and 10B, which may be optionally superimposed on the image of IMD 14’ in the GUI to enable a clinician to visualize the rotation of IMD 14’ about its longitudinal axis 22. Other landmarks or markings may be displayed superimposed on the image of IMD 14’ to enable visualization of the rotation of IMD 14' about its longitudinal axis 22. The landmarks, such as the reference line 376 (which may extend across the proximal end 28 of IMD 14’ and/or down the longitudinal sidew all of housing 15), may be aligned with the circumferential location of the tip of helical electrode 24 in some examples. External device processor 52 may append a determined roll waveform of IMD position by the roll angle at a time point t(i) to update the moving image of IMD 14’ and for tracking a turn count of IMD 14’.

[0121] External device processor 52 may update a count of the number of full cycles of the roll waveform, where each cycle of the waveform corresponds to one total 360 degree rotation of IMD 14’ around its longitudinal axis 22. The net number of turns in a clockwise direction around the longitudinal axis 22 from the starting position (of FIG. 9A) may be reported (shown arbitrarily as “N turns”) in the quantitative positional information 384 of FIG. 10B. When the roll angle increases in a clockwise direction from t(i-l) to t(i), the turn count may be increased. When the roll angle 382 decreases from t(i-l) to t(i), the turn count may be decreased to account for both counterclockwise and clockwise rotations of IMD 14’ that may occur.

[0122] A change in only pitch is represented by the images shown in the diagrams of FIGs. 9A and 9B, and a change in only roll is represented by the images shown in the diagrams of FIGs. 10A and 10B for the sake of clarity. It is to be understood that both pitch and roll angles may change between consecutive time points and can be determined at a given time point t(i) for comparison to the previous time point t(i-l) for determining both the new' pitch and roll and the direction of rotation relative to the x-axis to the new pitch and the direction of rotation relative to the y-axis to the new roll. The image of IMD 14’ may be dynamically rotated to the new pitch angle and the new roll angle concomitantly to produce the image representing the IMD position at t(i) and updated at each consecutive time point over a tracking time interval. [0123] FIG. 11 is a flow chart 500 of a method performed by processing circuitry of a medical device system for determining IMD positional information and providing feedback to a user during an implant procedure. Continuing with the example of IMD 14’ in communication with external device 50 for the sake of convenience, at block 502 control circuit 206 of IMD 14’ may receive the low pass filtered accelerometer axis signals representing the DC acceleration from accelerometer 212. The digitized, low pass filtered axis signals may be acquired at a desired sampling rate and transmitted to external device 50 via communication circuit 208. External device processor 50 may receive the accelerometer axis signal amplitudes via telemetry⁷ unit 58 at block 502. It is to be understood that, in other examples, IMD control circuit 206 may determine pitch and roll at each time point and transmit determined values to external device 50. [0124] At block 503, IMD control circuit 206 may detect when the distal electrode, e.g., electrode 24 shown in FIG. 4, makes tissue contact. An electrical measurement may be performed by IMD 14' for detecting contact of the distal electrode 24 with cardiac tissue. For instance, tissue contact may be detected based on an impedance measurement, e.g., a drop in impedance as the electrode 24 advances from the blood volume into contact with the tissue. Additionally or alternatively, tissue contact may be detected based on an increased amplitude of an EGM signal sensed using electrode 24 and/or detection of cardiac pacing capture, as examples. When tissue contact is detected, IMD 14' may transmit a signal to external device processor 52. External device processor 52 may set the turn count to zero as a starting value of the turn count. In some instances, rotation of IMD 14’ may occur within the delivery tool prior to engagement of electrode 24 with the cardiac tissue. Changes in the roll angle that occur prior to detecting tissue contact may be ignored for purposes of counting the net number of turns in a given direction. The net number of clockwise turns, for example, may be determined as an indication of the degree of fixation of the helical electrode 24 in the tissue. Other methods maybe used for detecting tissue contact, not limited to the electrical signal analysis examples given here. In general, any method for detecting tissue contact by the electrode 24 (or generally IMD distal end 26) may be used for establishing a zero turn count from which the determined roll angles are used to adjust the net total number of turns as IMD 14’ is rotated about its longitudinal axis.

[0125] At block 504, external device processor 50 may determine the pitch angle at a current time point t(i) according to the methods described above. At block 506. external device processor 50 may determine the roll angle at the current time point t(i) according to the methods described above. Processor 52 can be configured to determine the pitch angle and the roll angle relative to a local coordinate system axis (having a known relation to the accelerometer axes) using trigonometric relationships between the Al, A2 and A3 axis signal amplitudes and gravity. [0126] Target ranges for the angular positional information of IMD 14/14’ may be stored in memory' 53 of external device 50. For instance, an acceptable pitch and/or total turn count for a given IMD being implanted at an expected, target implant site (e.g., Triangle of Koch, target position along the interventricular septum, etc.) may be stored in memory' of the medical device system. External device memory' 53 may store an acceptable pitch angle range and an acceptable turn count range (e.g., total number of rotations around the IMD longitudinal axis 22) for promoting reliable fixation, reliable electrophysiological sensing, and/or reliable capture of adjacent body tissue by electrical pulses delivered by the IMD 14’. The acceptable pitch angle and, if relevant, the acceptable number of turns may be established from clinical data for a given implant location. In an illustrative example with no limitation intended, for a given implant location indicated for the IMD 14‘ and based on average or typical patient anatomy and/or other factors, the expected pitch angle of IMD 14’ may be 20 degrees and a range of 10 to 30 degrees may be acceptable.

[0127] At block 508, external device processor 52 may compare the pitch determined at t(i) to a target pitch or acceptable pitch angle range. If the pitch is not within the acceptable range of a target value, external device processor 52 may generate a user feedback notification at block 512. The user feedback notification may include an indication of the detection of tissue contact and/or electrical measurements associated therewith. Any of the example electrical measurements listed above that may be performed for detecting tissue contact may be displayed by display unit 54 of external device 50. The user feedback notification may include a prompt or instruction to the user to adjust the IMD position. For instance, the user feedback notification may be a textual or graphical representation of the determined pitch angle, the desired pitch angle and/or the difference between the determined and desired pitch angle. The user feedback notification may prompt the user to adjust the pitch angle by tilting the delivery' tool up or down to adjust the pitch into the acceptable pitch angle range. At block 514, the external device processor 52 may advance to the next time point to determine anew pitch angle at block 504. The process of blocks 504, 506, 508, 512 and 514 may be repeated in a loop while dynamically updating the GUI to indicate the IMD position and/or the pitch angle relative to a target pitch angle until the pitch angle is within an acceptable range as determined at block 508.

[0128] In some examples, at block 508 the external device processor 52 may detect when the A2 axis signal of accelerometer has a magnitude approximately equal to gravity, e.g., within 10% or other specified range of gravity⁷ (1 g or equivalent ADC units) . In this circumstance, the Al and A3 axes may be orthogonal to gravity making the pitch and roll indeterminable. The gravitational component along the Al and A3 axes may be zero. As such, external device processor 52 may generate a user feedback signal at block 512 for display by display unit 54 (or any of the user interfaces described herein) to prompt the user to adjust the position of IMD 14’ to change the angle of the longitudinal axis 22 (or more specifically the A2 axis of the accelerometer) relative to gravity when the A2 signal magnitude is equal to or within a threshold range of gravity. Conversely, when the Al axis signal or the A3 axis signal is near or at zero, a user feedback signal may be generated to prompt the user to change the angle of the longitudinal axis 22 of IMD 14’. For example, an "out of range’' message or other textual message and/or a prompt to change a positional angle of IMD 14’ may be displayed by a user interface of the medical device system at block 512. In this way, the Al and A3 axis sensor elements may resume producing acceleration signal components relative to gravity that can be used to compute pitch and roll angles.

[0129] After verifying an acceptable pitch angle, external device processor 52 may advance to block 510 to determine if the net total turn count determined from the roll angle waveform (as described above) is within an acceptable range. The turn count may begin at zero upon detecting tissue contact at block 503 and be updated at each subsequent time point t(i) based on the roll angle determined at block 506 for determining the cumulative net increases in roll angle. As such, the turn count may remain at zero turns until tissue contact is detected. Once tissue contact is detected, the turn count may increase (or decrease but not to a value less than zero) at each time point t(i) based on the change in roll angle. IMD 14’ may be considered to be adequately fixed at an implant site or sufficiently advanced in cardiac tissue for pacing and sensing when the turn count is at least 3. 4, 5, 6, 7. 8 or other recommended minimum number of turns.

Additionally or alternatively, the IMD 14’ may be considered to be adequately advanced into the implant site when the turn count is less than 8, 9, 10 or other recommended maximum number of turns in order to avoid over advancement of the distal electrode 24, e.g., past a desired pacing and/or sensing site or to avoid perforation of the heart wall. In an illustrative example, for a given implant site indicated for a given IMD, e.g., IMD 14’, an acceptable range of the number of turns (complete 360 degree rotations around longitudinal axis 22 of IMD 14’) is between 3.5 and 7 turns, with no limitation intended.

[0130] If the turn count is not within the acceptable range at block 510. external device processor 52 may generate an output at block 512 to control the display unit 54 to display a user feedback signal to instruct or prompt the user to adjust the number of turns. A textual, graphical and/or audible signal may be displayed or broadcast to indicate to the user that the turn count is either too low and additional rotations (e.g.. clockwise rotations) of the IMD are needed or that the turn count is too high and additional rotations (e.g., counterclockwise rotations) of the IMD are needed.

[0131] At block 514, the external device processor 52 may advance to the next time point and return to block 506 to determine the roll at the next time point for updating the turn count. In the example shown, external device processor 52 may optionally return to block 504 to redetermine the pitch angle for reconfirming that the pitch angle has not fallen outside the acceptable range. The process of blocks 506, 510, 512 and 514 (optionally along with blocks 504 and 508) may be repeated in a loop while dynamically updating the GUI to indicate the IMD position and/or the turn count relative to an acceptable range of the turn count. Once the turn count is determined to be in the acceptable range at block 510 and the pitch angle is still within the acceptable pitch angle range, external device processor 52 may confirm an acceptable implant position is achieved via a user feedback signal at block 516.

[0132] It is contemplated that in some instances, the pitch angle may be determined without determining a tum count, e.g., in the case of IMD 14 shown in FIGs. 1-3. A wholly circumferential abutment of the distal end 104 against body tissue 101 at the implant site may be desired to promote sufficient tissue engagement by all fixation tines 36 for reliable fixation. The pitch angle of IMD 14 may be an indication of whether the delivery tool receptacle 103 is angled at an expected pitch angle that corresponds to circumferential contact of the delivery tool distal end 104 so that all fixation tine tips 37 can penetrate body tissue 101 as IMD 14 is deployed from receptacle 103. Because fixation of IMD 14 provided with spring-loaded fixation tines does not require rotation of IMD 14 as in the case of IMD 14’ shown in FIGs. 4-6, the process of flow⁷ chart 500 shown in FIG. 11 may be performed without determining the turn count and comparing the turn count to an acceptable range. Once the pitch angle is within an acceptable range at block 508, the external processor 52 and display unit 54 may cooperatively confirm the implant position at block 516. The clinician may deploy IMD 14 from the delivery tool 102 upon confirmation of the implant position at block 516 based on a recommended pitch angle.

[0133] In some instances, after deployment, but before releasing tether 120 and withdrawing delivery tool 102, the external device processor 52 may continue to update the computed pitch angle and roll angle to continue displaying a dynamically moving graphical image of IMD position. In this way, a clinician can confirm that IMD 14/14' is stably positioned at the implant site, e.g.. without a high variation in pitch angle and/or roll that could indicate poor tissue engagement of one or more fixation tines 36 or distal electrode 24, respectively. If excessive motion of IMD 14/14’ is observed, the clinician may retract IMD 14/14' back into receptacle 103 for repositioning as needed and subsequent redeployment.

[0134] It is further contemplated that, in some examples, determination of pitch angle and/or the comparison of the pitch angle to an acceptable range may be omitted. The turn count and/or a final roll angle may be more significant in confirming a desired implant position and/or adequate fixation in some clinical applications. For instance, in the case of IMD 14’ having a helical screw in electrode 24 centered on its longitudinal axis 22, the turn count may be a greater determinate of reliable, stable fixation of IMD 14’ at the implant site and/or promote reliable positioning of distal electrode 24 at a pacing/sensing site rather than pitch angle. The pitch angle may still be determined by external device processor 52 for rendering a dynamically moving graphical image of IMD position as described above, but the comparison of the pitch angle to an acceptable range may be omitted in some applications of the techniques disclosed herein.

[0135] FIG. 12 is a diagram 550 of an image that may be displayed in a GUI by display unit 54. The graphical image of IMD 14’ is displayed relative to a local coordinate system that includes a z-axis aligned with gravity and an x-y plane perpendicular to gravity so that the position of IMD 14’ can be dynamically displayed relative to gravity and earth center as generally described above in conjunction with FIGs. 8-10B. In some examples, the graphical image of IMD 14’ may be overlaid or superimposed on an anatomical image of a heart 558. The graphical image of IMD 14’ may be positioned with the IMD distal end 26 at a target implant site of the anatomical image of the heart 558.

[0136] The distal end 26 of IMD 14’ may remain anchored at the target implant site, e.g., upon detecting tissue contact using any of the methods described above. The target implant site can correspond to the origin of the local coordinate system such that the dynamically moving graphical image of IMD 14’ may be adjusted to different pitch angles and roll angles as determined from the orientation signal without moving the distal end 26 from the local coordinate system origin, O. Here, distal end 26 of IMD 14’ is shown positioned at a target implant site in the Triangle of Koch 559, where distal electrode 24 may be advanced to a position for pacing the ventricles, e.g., from within the ventncular septum in the area of the His Bundle. In other examples, a different anatomical image of the heart 558 or portion thereof may be displayed according to the target implant site for a given device and clinical application, such as the interventricular septum, the right atrium, the left ventricle, the right ventricle, etc. Instead of a graphical anatomical image of the heart 558, it is further contemplated that the graphic image of IMD 14’ may be superimposed on a medical image obtained from the patient. For instance, the image of heart 558 may be a medical image obtained from the patient via fluoroscopy or another medical imaging method.

[0137] As described in conjunction with the flow chart 500 of FIG. 11, the external device processor 52 may determine the pitch angle 552, display the pitch angle in the quantitative positional information 554 and/or plotted relative to the y-axis (or x-y plane) of the local coordinate system as shown. A desired pitch angle 560 may be displayed graphically relative to the local coordinate system and/or as text in the quantitative positional information 554. In some examples, an acceptable range 562 of the pitch angle may be displayed, e.g., in the quantitative positional information 554 as show n and/or as a graphical depiction relative to the local coordinate system and the image of IMD 14’ as shown in FIG. 12. While the x-, y- and z-axes of the local coordinate system are shown in the example of FIG. 12 for the sake of illustration, in other examples the image of IMD 14’ may be displayed superimposed on a cardiac image 558 without the local coordinate system axes being displayed.

[0138] In other examples, the positional information displayed in a GUI may be displayed qualitatively in addition to or instead of quantitatively as shown in FIG. 12. For instance, a user feedback signal displayed by display unit 54 or user interface 56 may be a visual and/or audible feedback signal that communicates to the user when the pitch angle is within a recommended range and/or when the turn count is within a recommended range. For example, a visual display of IMD 14’ may change from red to green when the pitch and turn count are within their respective recommended ranges. As described above, an interface and control unit 109 of delivery tool 102 may generate a user feedback signal, which may include a tactile signal, when the pitch and turn count are within the respective ranges. Separate qualitative user feedback signals may be generated to indicate to the user when the pitch angle is out of range and provide a direction of adjustment (e.g., up or down) and to indicate to the user when the turn count is out of range and provide a prompt to turn clockwise or counterclockwise.

[0139] As described in conjunction with FIG. 11, external device processor 52 may determine the pitch angle 552 and compare the pitch angle 552 to the acceptable range 562 (and/or to the desired target pitch angle 560). As the position of the image of IMD 14’ is dynamically updated according to the pitch angle (and roll angle if determined), the external device processor 52 may generate an output to control display unit 54 to provide a user feedback signal indicating when the pitch angle 552 falls within the acceptable range 562. For example, the pitch angle displayed quantitatively in the positional information 554 may turn from red to green font or highlighted in another manner, an audible tone may be generated by the display unit 54 or user interface 56, a portion of the displayed image may change between a steady state and blinking state or other visual cue may be displayed to indicate to the clinician when IMD 14’ is rotated to a pitch angle within the acceptable angular range 562.

[0140] While a graphical indication of the roll angle is not shown in the example of FIG. 12, the quantitative positional information 554 may include a display of the turn count and a minimum to maximum acceptable range of the turn count. The display of the turn count may be adjusted, e.g., by changing the font color or other formatting, changing from blinking to non-blinking, or other visual cue, to indicate to the clinician when the turn count is within the recommended or acceptable range of a target total turn count. In some examples, when the pitch angle is w ithin the recommended range, a user feedback signal may be generated and displayed to prompt the clinician to begin rotating IMD 14’ about its longitudinal axis to begin turning helical electrode 24 into the adjacent tissue or to deploy IMD 14 from the delivery tool.

[0141] FIG. 13 is a flow' chart 600 of a method for determining IMD positional information and generating a dynamically moving graphical image of IMD position according to another example. At block 602, an image of the IMD in a nominal starting position is displayed by display unit 54. For the sake of example, FIG. 13 is described with reference to IMD 14’ as shown in FIGs. 4-6. The starting position may be displayed as shown in FIG. 9A as an example, with the longitudinal axis 22 of IMD 14’ aligned with the y-axis of a local coordinate system. [0142] At block 604, IMD 14' senses the three accelerometer axis signals and may transmit the low pass filtered, digitized axis signals to external device 50. At block 606. IMD 14’ senses three axis signals from a second orientation sensor, e.g., a magnetometer or gyroscope, having a reference vector that is orthogonal to gravity. By including a second orientation sensor having a reference vector orthogonal to gravity, the yaw' angle of the position of IMD 14’ relative to the local coordinate system can be determined so that the projected direction of the longitudinal axis 22 of IMD 14’ in the horizontal plane perpendicular to gravity is known.

[0143] At blocks 608 and 610, the external device processor 52 may determine the pitch angle and the roll angle at a current time point t(i) using the three accelerometer axis signals, e.g., according to the techniques described above in conjunction with FIG. 8. In this example, having a second 3D sensor with a reference vector orthogonal to gravity, the external device processor 52 may compute a yaw angle at block 612 for time t(i), using the second sensor axis signals. For example, if the second orientation sensor is provided as a magnetometer, a reference vector may be established by positioning a permanent magnet or an electrically conductive coil for generating a magnetic field external to the patient (as further described below in conjunction with FIG. 14). If the second orientation sensor is provided as a gyroscope, a reference vector may be established as the gyroscope signal when an IMD axis, e.g., the longitudinal axis 22 of IMD 14’. is known to be in a physical position that is perpendicular to gravity, as further described below in conjunction with FIG. 16.

[0144] The yaw angle may be determined at block 612 by determining the angle between the reference vector of the secondary' sensor and the three dimensional signal from the second orientation sensor. For example, the angle between the second reference vector (a magnetic field vector or an established gyroscope vector signal) and the 3D signal from the second orientation sensor may be computed as the inverse cosine of the dot product of the normalized 3D signal from the second orientation sensor and the reference unit vector. The projection of this angle in 3D space may be projected onto the x-y plane for determining the yaw angle at block 612. Other example methods for computing the yaw angle using secondary sensor orientation signals are described below in conjunction with FIGs. 14 -16.

[0145] At block 616, the IMD position displayed by display unit 54 may be adjusted by rotating the IMD 14’ to the determined pitch angle, roll angle and yaw angle at time t(i). The image of the IMD 14’ can be rotated clockwise or counterclockwise relative to the x-axis of the local coordinate system from the t(i-l) pitch angle to the t(i) pitch angle based on the sign of the change in pitch as described above. The image of the IMD 14’ can be rotated clockwise or counterclockwise relative to the y-axis of the local coordinate system from the t(i-l) roll angle to the t(i) roll angle based on the sign of the change in roll as described above. The image of the IMD 14’ can be rotated clockwise or counterclockwise from the t(i-l) yaw angle to the t(i) yaw angle with respect to the z-axis of the local coordinate system based on the sign of the change in yaw determined at block 614.

[0146] In some examples, external device processor 52 may compare the pitch angle to a target pitch angle range for a given clinical application at block 618. Additionally or alternatively, external device processor 52 may compare the roll angle and/or turn count determined from the appended roll waveform as described above to a target roll angle range or target turn count range, respectively. Additionally or alternatively, in some examples external device processor 52 may compare the yaw angle to a target yaw angle range for a given clinical application at block 618. For example, for a target implant site, such as within the Triangle of Koch as generally shown in FIG. 12, along the interventricular septum or other target site for a given IMD, the target range for pitch, turn count, roll, and/or yaw may be stored in external device memory 53. When a target range is not met by the IMD positional data, as determined at block 618, external device processor 52 may generate an output at block 620 for causing display unit 54 to generate a user feedback signal that instructs, prompts or otherwise notifies the user that an adjustment of the IMD position is recommended. Example user feedback signals that may include graphical, textual and/or audible signals are generally described above in conjunction with FIG. 12.

[0147] External device processor 52 may advance to the next time point at block 622 and redetermine the pitch, roll and yaw angles at blocks 608, 610 and 612 respectively at the next time point for updating the displayed image of IMD 14’ in a dynamic manner as the IMD position changes, e.g., in real time. When the IMD positional data meets one or more target ranges for an acceptable or recommended implant position as determined at block 618, external device processor 52 may generate a user feedback signal confirming the acceptable implant position at block 624. Generating the dynamically moving IMD image may be terminated upon confirming the implant position or may continue until the user exits the IMD image tracking function on external device 50.

[0148] FIG. 14 is a diagram 650 of a patient 652 who may be implanted with IMD 14’. The patient 652 may be in a supine position during the implant procedure, as shown, or in another appropriate position for the implant procedure. In this example, the orientation sensor 240 of IMD 14 may include accelerometer 212, represented in FIG. 14 by the three accelerometer axes Al, A2 and A3, and a secondary sensor 242 (see FIG. 7) that includes a three-axis magnetometer represented in FIG. 14 by the three orthogonal Ml, M2 and M3 axes. While the three magnetometer axes are shown aligned in the same directions as the three accelerometer axes in this example, the three orthogonal magnetometer axes may have a different orientation in other examples. During an implant or other procedure that involves adjusting the position of IMD 14’, IMD 14’ may transmit the three axis signals from accelerometer 212 and the three axis signals from the secondary sensor 242, in this case magnetometer signals, and/or data derived therefrom to external device 50 for generating a dynamic display of the position of IMD 14’.

[0149] IMD 14’ may be displayed as having a nominal starting position that assumes the Al axis is aligned with the vertical z-axis of a local coordinate system that extends parallel to gravity 654. In this nominal starting position, the A3 axis may be aligned with the x-axis, and the A2 axis may be aligned with the y-axis of the horizontal plane. As described above, the external device processor 52 may determine the pitch angle of IMD 14’ as the rotation 662 around the x- axis from the A2 axis signal of accelerometer 212. External device processor may determine the roll angle of IMD 14’ as the rotation 664 around the longitudinal axis 22 from the Al and A3 axis signals. The yaw angle, determined as the rotation 666 around the z-axis may be indeterminable from the accelerometer signals because the z-axis is parallel to gravity 654 such that rotation around the z-axis, in the x-y plane, does not result in variation of the accelerometer axis signals. [0150] A second reference vector 672 may be provided that is orthogonal to gravity 654 for sensing rotation 666 of IMD 14 with respect to the vertical z-axis. Reference vector 672 may be provided, for example, by aligning a magnetic field vector of a permanent magnet or an electrically conductive coil with an axis 656 of patient 652 that is in the x-y plane, perpendicular to gravity 654. In the example shown, a magnetic field device 670 may be positioned along the patient 652 to provide a magnetic field reference vector 672 that is aligned with a long axis 656 of the patient 652, e.g., a cranial-caudal axis, when the patient 652 is in a prone or supine position.

[0151] In other examples, the magnetic field device 670 may be positioned to align the second reference vector 672 along a frontal axis, e.g.. extending right to left with respect to the patient when the patient is in a supine, prone or upright position. The alignment of the second reference vector 672 relative to an axis of the patient that is orthogonal to gravity 654 (serving as the first reference vector for accelerometer 212) can provide a reference angular position defined by the magnetometer vector signal of a zero yaw angle (or other designated yaw angle).

[0152] Magnetic field device 670 may include a permanent magnet or an electrically conductive coil and may be incorporated in a programming head coupled to external device 50, for example. External device processor 52 may control electrical current passed to the coil from external device 50 in a continuous or intermittent manner to generate the magnetic field vector that defines the second reference vector 672. In other examples, the magnetic field device 670 may be a stand-alone device provided for the purpose of establishing the second reference vector 672 for the secondary’ sensor 242 for sensing orientation signals relative to the second reference vector 672. The magnetic field device 670 may be positioned by a clinician relative to the patient 652 during an IMD implant or follow up procedure for establishing the second reference vector 672 as appropriate, e.g., in the horizontal plane perpendicular to gravity 654, for a given patient position with respect to gravity.

[0153] External device 50 may receive magnetometer signals from the three axes Ml, M2 and M3 of the secondary sensor 242 as the position of IMD 14’ is changed during advancement to an implant site and/or during positional adjustments of IMD 14’ upon reaching an implant site, prior to or during deployment of IMD 14’ from the delivery tool. After implant or during a follow up procedure, external device 50 may receive magnetometer signals from the three axes Ml, M2 and M3 from IMD 14' as the position of IMD 14' is changed during motion imparted on IMD 14’, e.g.. due to the cardiac cycle, respiratory cycle or other patient body motion.

[0154] External device memory 53 may store the x, y and z components defining the direction of the reference vector 672, e.g., as a unit vector [0, 1, 0], At any given time t(i), external processor 52 may determine the difference between the reference vector 672 and the magnetometer vector signal [m3, m2, ml], which may be normalized as a unit vector. The angle between the reference vector 672 and the unit vector representing the magnetometer vector signal may be determined based on the difference between the magnetometer vector signal and the reference vector. As described below, the yaw angle of rotation 666 about the z-axis of the local coordinate system, which may be indeterminable from the accelerometer axis signals alone, can be determined using the magnetometer vector signal.

[0155] FIGs. 15A — 15C are diagrams depicting a method for determining the yaw angle of the IMD according to some examples. FIG. 15A is a diagram 750 of an acceleration vector 752 and a magnetometer vector 756 determined from the 3D acceleration signal and the 3D magnetometer signal, respectively, at a given time point. In FIG. 15 A, a hypothetical acceleration vector 752 ([al, a2, a3]) is shown for a given position of IMD 14’ at a given time point relative to gravity 754. The acceleration vector 752 is defined by its individual axis signal components a(Al). a(a2) and a(A3). A hypothetical magnetometer vector 756 ([ml, m2, m3]) is shown in FIG. 15 A for the given position of IMD 14’ at the same time point that the acceleration vector 752 is obtained. The magnetometer vector 756 is defined by its individual axis signal components m(Ml), m(M2) and m(M3) measured relative to the reference magnetic field vector B 758. The spatial relationship between the orientation sensor element axes, e.g.. the Al. A2 and A3 axes of accelerometer 212 and Ml, M2 and M3 axes of magnetometer 242 as shown in FIG. 14, is fixed within the IMD (e.g., IMD 14’), such that the 3D acceleration vector 752 and the 3D magnetometer vector 756 can be reflected into a unified vector space based on their know n spatial relationship to each other.

[0156] FIG. 15B is a diagram 760 of the unified acceleration vector 762 and a magnetometer vector 766 after reflection into the unified vector space. The unified vector space may be defined by the local x-, y-, z-coordinate system, which can be defined relative to gravity 754, and the patient may be in a known posture relative to gravity 754, e.g., supine or other specified position. The reference magnetic field vector B 758 can be established as shown in FIG. 14 to align with a given axis of the local coordinate system that is orthogonal to gravity 754.

[0157] The unified vector space contains both of the orientation sensor signal vector reflections, in this case reflected acceleration vector 7 2 and reflected magnetometer vector 766, for the IMD position in the local coordinate space. This unification of the two 3D vector signals may involve transforming, via sign and/or rotation, at least one of the 3D vectors, e.g., the magnetometer vector signal, such that movement of IMD 14’ to a new position results in unified movement of both of the acceleration vector and the magnetometer vector within the same spatial domain defined by the local coordinate system. The transformed, reflected magnetometer vector 766 may be denoted by [ml’, m2’, m3’].

[0158] FIG. 15C is a diagram 770 of the orthogonal components of the reflected magnetometer vector 766 (of FIG. 15B) in the unified space. After unification (as shown in FIG. 15B), the components of the transformed, reflected magnetometer vector [ml’, m2’, m3’] that are orthogonal to gravity 754 may be obtained by projection onto the x-y plane of the local coordinate system. The magnitudes of the gravity orthogonal components of the reflected magnetometer vector [ml ’, m2’, m3’] may be given by the scalar projection [Ml’, M2’] having a rotational magnitude determined using the pitch angle 764 (FIG. 15B) of IMD 14’. The pitch angle 764 can be determined from the accelerometer vector signal as the angle of rotation 662 around the x-axis as shown in FIG. 14 according to the methods described above.

[0159] The gravity orthogonal scalar projection [Ml ’, M2’] 776 of the reflected magnetometer vector [ml’, m2', m3’] 766 may be determined by the absolute value of the ml’ and m2' amplitudes times the cosine of the pitch angle 764 (shown in FIG. 15B), determined from the accelerometer vector signal as the angle of rotation about the x-axis (see rotation 662 in FIG. 14) as described above. This scalar projection [Ml’, M2’] decomposes the transformed magnetometer vector 766 (shown in FIG. 15B) into only gravity' orthogonal components, which may be referred to as Ml’ and M2’. The third component M3’ (not shown in FIG. 15C) that is parallel to gravity 754 is not needed to determine the yaw angle 788 as the degree of rotation 786 of IMD 14’ about the z-axis of the local coordinate system.

[0160] The yaw angle 788 may be determined by the processing circuitry of the IMD system as the inverse tangent of the projected, reflected magnetometer vector signal components Ml ’ divided by M2’, for example. While FIGs. 15A — 15C represent one method for determining the yaw angle, other methods may be used for computing the pitch, roll and yaw at each time point using a combination of the 3D accelerometer signal and the 3D magnetometer signal, which may be output by an IMU in some examples, having orthogonal reference vectors (gravity 754 and magnetic field B 758).

[0161] As described above in conjunction with FIG. 13, the position of the image of IMD 14’ can be adjusted in the graphical display to the currently determined yaw angle 788 at time t(i). The image of IMD 14’ may be rotated around the z-axis, as shown by rotational arrow⁷786, to the yaw angle 788 in either a clockwise or counterclockwise direction. The direction of rotation from the preceding yaw angle to yaw angle 788 is selected to correspond to an increase or a decrease in the yaw angle, respectively, from the previous yaw angle at time point t(i-l). In this way, a moving graphical image of IMD 14’ can be adjusted from one time point to the next according to a change in pitch, roll and/or yaw.

[0162] FIG. 16 is a diagram 700 of patient 652 depicting another method for establishing a reference vector for a secondary sensor of orientation sensor 240 according to another example. In this example, the orientation sensor 240 of IMD 14’ may include accelerometer 212, represented in FIG. 16 as the three accelerometer axes Al, A2 and A3, and a secondary sensor 242 (see FIG. 7) that includes a three-axis gyroscope represented in FIG. 16 by the three orthogonal VI, V2 and V3 axes. During an implant or other procedure that involves adjusting the position of IMD 14’ or determining the motion of IMD 14’ due to imparted forces, IMD 14’ may transmit the three axis signals from accelerometer 212 and the three axis signals from the secondary sensor 242 (and/or data derived therefrom), in this case signals correlated to the angular velocity of IMD 14’ along each VI, V2 and V3 axis. External device 50 may receive the orientation sensor signals and/or data derived therefrom for generating a dynamic display of the position of IMD 14’.

[0163] An image of IMD 14’ may be displayed by display unit 54 of external device 50 with IMD longitudinal axis 22 represented in the image. The user may be prompted to position the image of IMD 14’ so that it’s longitudinal axis 22 is aligned with the y-axis of the local coordinate system 702 at a time that the user can confirm that the IMD 14’ is positioned with its longitudinal axis 22 aligned with a long axis 656 of the patient 652. parallel to the y-axis of the local coordinate system, which is orthogonal to gravity 654.

[0164] The GUI displayed by display unit 54 may generate a user prompt 704 to instruct the clinician to first confirm that the IMD longitudinal axis 22 is substantially aligned with the long axis 656 of the patient (or another reference axis orthogonal to gravity). For example, the clinician may position IMD 14’ externally to the patient (such as on the patient’s chest) with the IMD 14’ longitudinal axis 22 parallel to a long axis 656 of the patient. The clinician may confirm that the position of the IMD 14’ longitudinal axis is aligned in a horizontal plane, e.g., lengthwise with the patient. For example, the displayed prompt may include a checkbox or other confirmation prompt for the clinician to mark to confirm the IMD alignment relative to a desired patient axis is in the horizontal plane perpendicular to gravity. In other instances, the clinician may begin advancing IMD 14’ within the patient’s body using delivery tool 102. When the delivery tool receptacle is in an anatomical location known to align the IMD longitudinal axis 22 lengthwise with the long axis 656 of patient 652, the clinician may confirm that the position of the IMD 14’ longitudinal axis is aligned with the patient lengthwise in the horizontal plane orthogonal to gravity' 654. [0165] Once the IMD position relative to the patient in an orthogonal plane relative to gravity is confirmed, the clinician may be prompted by the GUI (as shown in user prompt 704) to adjust the displayed image of IMD 14’ to align the displayed longitudinal axis 22 of IMD 14’ with the displayed y-axis of the local coordinate system. Using a mouse, keyboard, touch screen or other user interface device, the clinician may adjust the IMD image to align the displayed longitudinal axis 22 with the Y-axis of local coordinate system 702 as needed.

[0166] In this way, a reference gyroscope vector signal being received when the IMD 14’ is in a confirmed alignment position relative to the patient and the horizontal plane orthogonal to gravity can be confirmed as a reference vector signal corresponding to a designated yaw angle, e.g., a zero yaw angle of rotation about the z-axis. It is contemplated that in other examples, a zero degree yaw angle may be defined as alignment of the IMD longitudinal axis 22 with the x- axis, pointing right or pointing left with the patient, such that the clinician may be prompted to align the IMD longitudinal axis 22 with the x-axis when IMD 14' is known to be aligned with a lateral axis of patient 652, orthogonal to gravity 654.

[0167] The user prompt 704 may be displayed by display unit 54 at the start of the process initiated by the user for generating the dynamically moving IMD image. The user prompt 704 may disappear after the clinician adjusts the image of the IMD 14’ to align longitudinal axis 22 with the displayed y-axis (or other reference axis orthogonal to gravity defining a starting angle of rotation about the z-axis). It is to be understood that the patient 652 need not necessarily be in a supine position for the techniques described in conjunction with FIGs. 13-15 to be performed. The patient may be in another position, e.g., prone, side lying, upright, etc. The magnetic field device 670 (FIG. 14) or the IMD longitudinal axis 22 may be positioned relative to an axis of the patient’s body to establish a secondary sensor reference vector position that is orthogonal to gravity 654 and selected to define to a designated yaw angle, e.g., zero degrees.

[0168] After confirming a reference yaw angle position as described in conjunction with FIG. 1 , external device 50 may receive gyroscope signals from the three axes VI, V2 and V3 of the secondary sensor 242 as the position of IMD 14’ is changed during advancement to an implant site and/or during positional adjustments of IMD 14’ upon reaching the implant site, prior to and/or during deployment of IMD 14’ from the delivery' tool. The VI, V2 and V3 axis signals of the secondary sensor 242 provided as a gy roscope in this example may be received during and after deployment of IMD 14’ to evaluate the motion of IMD 14’ before and after fixation or at any time post-implant. External device memory 53 may store the x. y and z components (e.g., v3, v2, and vl, respectively) of the gyroscope signal vector when positioned in the reference vector position, e.g., with IMD 14’ aligned lengthwise with the long axis 652 of the patient. IMD control circuit 206 or external device processor 52 may receive the gyroscope axis signals and integrate the sensed angular velocity from each axis signal over time to obtain a 3D angular position vector [x, y, z] of IMD 14’. At any given time t(i), external processor 52 may determine the difference between the reference gyroscope vector signal corresponding to zero degrees yaw and the gyroscope vector signal vector at t(i), which may be normalized as a unit vector.

[0169] The yaw angle between the y-axis of the local coordinate system and the longitudinal axis 22 of IMD 14’ projected on the horizontal x-y plane may be determined based on this vector difference. For example, the yaw angle may be determined by performing the transformation generally described above in conjunction with FIGs. 15A-15C. The 3D acceleration vector signal and the 3D gyroscope vector signal may be unified into the same spatial domain defined by the local coordinate system by transforming the 3D gyroscope signal (vl, v2, v3) by rotation and/or sign change to obtain (vl’, v2’, v3’) that moves with the accelerometer signal vector as the IMD 14’ is moved. The transformed gyroscope vector signal may be projected onto the x-y plane to obtain a scalar containing the components orthogonal to gravity, e.g., VI’ and V2’. The yaw angle at a given time t(i) may be computed as the arctangent of the ratio ofVl’ to V2’. As described above in conjunction with FIG. 13, the position of IMD 14’ can be adjusted in the graphical display of IMD 14’ to the currently determined yaw angle at time t(i) by rotating IMD 14' around the z-axis to the yaw angle in a clockwise or counterclockwise direction that corresponds to an increase or a decrease in yaw angle from the previous time point t(i-l).

[0170] FIG. 17 is a diagram 800 of a processing circuit configured to analyze IMD positional data for determining a dislodgement risk of an IMD at an implant site according to some examples. The processing circuit, shown as dislodgement risk predictor (DRP) 802, can be a machine learning model trained using a machine learning algorithm having multiple input channels 810 — 820. DRP 802 may be implemented in external device processor 52 or another computing system, which may be a computing device or cloud based processor included in a remote patient monitoring system or other external device. In some examples, DRP 802 may be implemented in whole or in part in control circuit 206 of IMD 14/14’.

[0171] DRP 802 may be configured to output a dislodgement risk 830 based on at least one IMD position input signal, e.g., the pitch 810 and/or turn count 812. While not shown in the illustrative example of FIG. 17, it is further contemplated that an input signal received by DRP 802 can be the yaw when the yaw angle is determined, e.g., using a secondary sensor as described above in conjunction with FIGs. 13-15. For example, the yaw angle could be substituted for the pitch 810 or provided in addition to the pitch 810 as an input to DRP 802. [0172] In the illustrative example shown in FIG. 17, DRP 802 may receive the input signal for pitch 810 and/or the turn count 812 at a given time point t(i), which may be selected by the user, e.g., when IMD 14/14’ is positioned against body tissue at an implant site, before and/or after deployment from delivery tool 102 (e.g., before and/or after fixation of IMD 14/14’ at the implant site via fixation tines 36 or distal helical electrode 24, respectively, as shown in FIGs. 3 and 6 for example). In some examples, an IMD position input signal, e.g., provided as pitch 810, may be a signal that is the appended pitch angle waveform determined over one or more cycles of a cardiac signal. In other examples, the IMD position input signal, e.g., provided as pitch 810, may be the pitch angle averaged over one or more cardiac cycles. In still other examples, the IMD position input signal, e.g., provided as pitch 810, may be received as a continuously sampled signal as the IMD position is determined from the orientation sensor signals in real time such that the dislodgement risk 830 output by DRP 802 may be displayed as a dynamically changing value or waveform by display unit 54.

[0173] In some examples, DRP 802 may receive a pitch angle range 814 as an input signal. Instead of or in addition to receiving a pitch angle waveform over at least one cardiac cycle (or other physiological cycle such as respiration), the medical device system processing circuitry may determine the average, the range, the average maximum, and/or the average minimum pitch angle or other representative value(s) of pitch over a specified time interval, e.g., one or more cardiac cycles. While not shown in the illustrative example of FIG. 17, the roll angle may be input to DRP 802 in addition to or instead of pitch 810. The roll angle could vary, e g., as IMD 14/14’ is subjected to cardiac motion after fixation of IMD 14/14’ at the implant site. As such, a roll angle waveform and/or one or more representative values of the variation of roll angle over one or more cardiac cycles may be determined by the processing circuitry and input to DRP 802. [0174] The pitch 810, turn count 812, and pitch angle range 814 are shown in FIG. 17 as illustrative examples of input signals that may be received by DRP 802 relating to the IMD positional data determined by external device processor 52. It is recognized that a number of IMD position related input signals may be provided to DRP 802 that can be produced by the medical device system processing circuitry as the instantaneous value of the pitch, roll, turn count, and/or yaw are determined according to the example methods presented herein and/or data is derived from the instantaneous values, e.g., a waveform appended over a specified time interval or a mean, median, maximum, minimum, range or other representative value(s) determined over a specified time interval from the determined pitch, roll and/or yaw angles.

[0175] In some examples, DRP 802 may receive other input signals that may relate to reliable or stable implant position of IMD 14/14’. For instance, a pacing capture threshold may be determined by IMD control circuit 206 by performing a pacing capture test. IMD control circuit 206 may control pulse generator 202 to deliver pacing pulses at multiple pulse outputs (e.g., multiple pulse amplitudes and/or pulse widths) and determine capture and loss of capture based on signals sensed by sensing circuit 204. IMD control circuit 206 may perform a pacing electrode impedance measurement. IMD control circuit 206 may control the pulse generator 202 and sensing circuit 204 to deliver an impedance drive signal and sense the resulting signal across electrodes 16 (or 24) and 18, for example. IMD control circuit 206 may determine a feature of a cardiac electrical signal sensed using IMD electrodes, e.g., electrodes 16 (or 24) and 18. For instance, IMD control circuit 206 may determine a mean peak amplitude that may correspond to a mean P-wave peak amplitude or a mean R-wave peak amplitude. As such, DRP 802 may be configured (e.g., trained) to receive input signals relating to the electrical stimulation function and/or cardiac electrical signal sensing function of IMD 14/14’, determined by IMD control circuit 206 and transmitted to external device 50 for inputting to DRP 802. In the example shown. DRP 802 may receive a pacing capture threshold 816. pacing impedance 818 and/or mean or median peak amplitude 820 determined from a sensed cardiac depolarization signal, e.g., P-wave or R-wave amplitude.

[0176] DRP 802 can be trained using input signal datasets from a population of patients using a supervised deep learning technique such as convolutional neural networks (CNN), residual CNN, feed-forward neural network (FFNN), recurrent neural network (RNN), transformer, or other machine learning techniques such as decision tree, random forest model, or other machine learning approaches to build a machine learning model, e.g., a neural network model, using the signal inputs received by DRP 802 for predicting a dislodgement risk. Inputs received by DRP 802 during a training session may be acquired in an analogous manner, e.g., using the same signal acquisition, processing and analysis techniques, as the signals that wil 1 be acquired for inputting to DRP 802 for predicting dislodgement risk after training is complete and the machine learning model is fixed.

[0177] A DRP training dataset may be obtained from each one of multiple patients, with each dataset including the required input signals. The multiple datasets obtained from multiple patients can define an “epoch” that may be input to DRP 802 multiple times during a training session. Training may be complete after a fixed number of epochs, e.g., the entirety of the training datasets from the population of patients has been passed to the DRP 802 a fixed number of times. In other examples, the DRP training may be stopped once the dislodgement risk outputs 830 and associated confidence levels have not changed more than a specified amount for one or more recent epochs. In some examples, training data may be obtained from benchtop or laboratory studies performed to simulate human implant conditions.

[0178] The trained machine learning model of DRP 802 may be validated by inputting validation datasets obtained from one or more patients. The validation datasets may be different than the training datasets but acquired in analogous manner. The validation datasets may be from a different or smaller group of patients than the training datasets. The output dislodgement risk 830 of DRP 802 resulting from input validation datasets can be validated by expert truthing of instances of actual dislodgement or no dislodgement of the IMD. The training of DRP 802 may be complete when the validation of the DRP output during training and/or validation by an expert has reached a certain threshold, which may be a low threshold percentage of false dislodgement classifications and/or high threshold percentage of true dislodgement predictions according to actual dislodgements truthed by an expert.

[0179] The output dislodgment risk 830 of DRP 802 can include an indication of dislodgment risk as a probability, e.g., on a range of 0 to 1 or 0 to 100. where a higher value indicates a relatively higher likelihood of IMD dislodgment. In some examples, the output dislodgment risk 830 may include a confidence level. The output dislodgment risk 830 of DRP 802 may be used by external device processor 52 for generating data for display by display unit 54. For instance, a probability value of dislodgement risk may be displayed in the GUI on display unit 54 with the dynamic image of IMD 14/14’ as the positional data is being determined. The output dislodgment risk 830 obtained after a capture threshold test, impedance measurement, and/or cardiac signal feature determination may be used by external device processor 52 for generating a final dislodgment risk 830 after deployment of the IMD 14/14’ at the implant site. In some examples, therefore, DRP 802 may be trained to output a first dislodgment risk using inputs relating to IMD position, e.g., inputs 810, 812, and 814 prior to IMD deployment from the delivery tool. DRP 802 may be trained to output a second dislodgment risk using the inputs relating to IMD position and one or more additional inputs relating to IMD sensing and therapy delivery performance, e.g., capture threshold 816. impedance 818 and/or peak amplitude 820, after fixation of IMD 14/14’ (e.g., deployment of fixation tines 36 or advancement of distal electrode 24 into body tissue). IMD 14/14’ may still be held by delivery tool tether 120 and/or partially retained by receptacle 103 (see FIG. 3 and FIG. 6).

[0180] External device processor 52 may compare the dislodgment risk to a threshold risk and generate a user feedback signal for display in the GUI. For example, when the dislodgment risk is greater than a threshold risk value, IMD repositioning may be recommended. When the dislodgment risk is equal to or less than the threshold risk value, the user feedback signal may indicate that the IMD position is acceptable. The threshold risk value may be between 0%. 0.1%, 0.5%, 1%, 5% or 10% as examples.

[0181] FIG. 18 is a diagram 850 of a GUI that may be displayed by external device 50 on display unit 54 including a dislodgment risk determined by DRP 802 of FIG. 17. The GUI may include the IMD positional information 852, a dislodgment risk profile window 854, and a dynamically moving graphical image 856 of IMD position displayed according to a determined pitch, roll and yaw (if determined) as described above(optionally relative to a local coordinate system and/or superimposed on an anatomical image as shown in FIG. 12).

[0182] The IMD positional information 852 may display a computed pitch angle, roll angle (not shown in FIG. 18). total net turn count determined from the cumulative roll angles up to the current time point, and yaw angle (if determined). The IMD positional information 852 may include a display of recommended ranges (e.g., recommended minimum to maximum values) for each of the respective pitch angle, turn count and yaw angle that is displayed. When a given IMD position measurement falls within the recommended range, the displayed value, e.g.. pitch angle, turn count or yaw, may turn from red to green, become highlighted or otherwise formatted in a distinguishing manner that indicates to the clinician that the IMD position measurement is in a desired range, e.g., for a given anatomical implant location, IMD model, etc. In some cases, one of the displayed angular position quantities may meet the desired or acceptable range displayed and another may not such that the qualitative feedback provided in the positional information 852 can prompt the user to continue adjusting the IMD position or stop adjusting the IMD position.

[0183] In addition to or alternatively to displaying quantitative positional information 852 as shown in FIG. 18 and other diagrams presented herein, a user interface of the medical device system, e.g., the user interface 56 of external device 50, a delivery tool interface, or a programming head user interface, may be configured to display or broadcast a user feedback signal indicative of qualitative positional information 853. For instance, the qualitative positional information 853 may include LEDs, displayed buttons or icons, or other indicators that change between red and green, solid to blinking, or in another distinguishing manner to indicate to the clinician when the pitch, total turn count, and/or yaw are within the recommended ranges for a given implant site of the IMD 14’, when the patient is in a known position relative to gravity⁷. For instance, when all three indicators of qualitative positional information 853 are green, the user can confirm that the position of IMD 14’ is in a recommended position relative to earth center for the given implant site and patient position relative to gravity. It is recognized that numerous variations of schemes for presenting qualitative positional information to a user for indicating when the pitch, turn count, and/or yaw meet recommended implant values or ranges can be conceived for display or broadcasting as a visual, audible and/or tactile user feedback signal by external device display unit 54, delivery tool 102 or other user interface device of the medical device system. Visual qualitative positional information may be displayed as a colored light or symbol and/or text information, for example, affirming a recommended range is met by the angular position data.

[0184] The dislodgment risk profile window 854 may display the output dislodgment risk 830 of DRP 802 (shown in FIG. 17) and may indicate whether IMD repositioning is recommended or not. The dislodgement risk and the repositioning recommendation may be displayed in red or other distinct formatting if the dislodgment risk is greater than a threshold value. The dislodgement risk and the repositioning recommendation may be displayed in green or other distinct formatting when the dislodgment risk is less than a threshold value and repositioning is not recommended. The dislodgment risk profile window- 854 may include a display of other data that relates to the IMD fixation stability and reliability; which may include other DRP inputs as described above. The data relating to IMD fixation stability and reliability may include a pitch range, e.g., as measured over a cardiac cycle as an indication of IMD stability with cardiac motion. The data relating to IMD fixation stability and reliability may include a roll and/or yaw⁷ range, e.g., as measured over a cardiac cycle as an indication of IMD stability with cardiac motion. The data relating to IMD fixation stability⁷ and reliability may include a pacing capture threshold, pacing impedance, and/or cardiac electrical signal peak amplitude, mean amplitude or other cardiac electrical signal strength indication. In the example shown, the cardiac electrical signal strength is represented by an average maximum R-wave peak amplitude.

[0185] In this way. the output of DRP 802 shown in FIG. 17 may be combined with the dynamic display of a graphical image of the IMD as it is moving in real time, quantitative IMD positional information and/or qualitative IMD positional information for providing valuable user feedback relating to the position and fixation of the IMD without requiring other types of medical imaging, such as fluoroscopy or ultrasound, throughout the procedure of implanting or assessing IMD fixation. Determining the IMD position and displaying a moving image of the IMD in a real time scale is not practically performed by human mental processes, e.g., during an IMD implant procedure. As such, the techniques disclosed herein provide meaningful improvements to computer-based processing methods for generating user feedback for guiding implantation of an IMD and for assessing the implant position and fixation after implantation.

[0186] FIG. 19 is a diagram of a medical device system 900 that may be configured to perform the techniques disclosed herein according to another example. In FIG. 19, external device 950 may generally correspond to external device 50. described above, having a display unit 954 and a processor, memory, user interface, and telemetry unit (not shown in FIG. 19). In this example, an IMD 914, which may be a cardiac pacemaker or implantable cardioverter defibrillator (ICD) as examples, may be implanted outside the patient’s heart, e.g., in a subcutaneous or submuscular location, and be coupled to a medical electrical lead 910. The medical electrical lead includes an elongated lead body 911 having a connector assembly (not shown) at the proximal lead end 928. The connector assembly can be coupled to a connector block 913 of IMD 914, e.g., by insertion into a connector bore of connector block 913, for electrically and mechanically coupling lead 910 to IMD 914.

[0187] The lead body 911 has a distal end 926 and may carry one or more electrodes 916 and 918 and/or other sensors for sensing cardiac signals. Lead 910 includes an orientation sensor 912, which may include at least an accelerometer 212 (not shown in FIG. 19). The accelerometer included in orientation sensor 912 may include at least a 3D accelerometer for passing acceleration signals to IMD 914 via electrical conductors extending through lead body 911. Insulated electrical conductors extending through one or more lumens of lead body 911 provide electrical connection betw een electrodes 916 and 918 and orientation sensor 912 and the connector assembly of proximal lead end 926 for carrying signals sensed by electrodes 916, 918 and orientation sensor 912 to IMD 14 and for carrying electrical signals to electrodes 916, 918 (such as pacing signals, impedance measurement drive signals, etc.) and to orientation sensor 912 (e g., for powering the orientation sensor elements).

[0188] The distal end 926 may be advanced into the patient’s heart 8 for positioning a distal electrode 916 at a desired cardiac pacing and/or sensing site, e.g., along or into the interventricular septum 9 though other locations are possible. Lead 910 may be advanced through the lumen of a guide catheter 940 to facilitate navigation and deployment of the lead 910. During an implant procedure and/or after implantation of lead 910, IMD 914 may receive orientation sensor signals from orientation sensor 912 for processing and analysis by processing circuitry of the medical device system 900, e.g.. by a control circuit of IMD 914, by processing circuitry of external device 950, by a remote computer processor (e.g., computing device 74 shown in FIG. 1) and/or by cloud-based processing on netw-ork/cloud 75 (shown in FIG. 1). [0189] According to any of the examples described above, the processing circuitry' may determine a pitch, roll and/or yaw of the distal end 926 of lead 910. A GUI presented by display unit 954 may display a dynamically moving image 956 of the lead distal end 926 and/or quantitative or qualitative positional data according to any of the examples described above. In some examples, a dislodgment risk may be determined by DRP 802 of FIG. 17 and displayed by display unit 954, e.g., as described in conjunction with FIG. 18.

[0190] During an implant procedure the proximal end 928 of lead 910 may be connected to IMD 914 for enabling electrical measurements to be performed and/or for acquiring the orientation sensor signals for analysis and/or transmission to external device 950. It is to be understood that in some examples, prior to connecting lead 910 to IMD 914, lead 910 may be temporarily coupled to an external device, such as a pacing system analyzer (PSA) 960, for performing electrical measurements. A PSA 960 can be used for obtaining electrophysiological measurements, determining pacing capture threshold, performing lead impedance measurements, measuring R-wave amplitude or the like, e.g., during an implant procedure. The PSA 960 may additionally be configured to perform analysis of the orientation sensor signal for determining distal lead end positional data or transfer the orientation sensor signal to external device 950. [0191] In some examples, in addition to or alternatively to the orientation sensor 912 carried by lead 910. the delivery took in this case a guide catheter 940, may include an orientation sensor 942 at or near its distal end. The orientation sensor 942 may be coupled to electrical conductors extending to the proximal handle of the guide catheter 940. The orientation sensor signals may be transmitted to external device 950, for example, by wireless or wired communication link 957 between guide catheter 940 and external device 950. In this way, the pitch, roll and/or yaw of the distal end of guide catheter 940 may be determined by processing circuitry of the medical device system 900 so that a dynamically moving image of the distal portion of the guide catheter 940 and/or quantitative or qualitative positional data may be displayed to a user by external device 950 in any of the manners disclosed herein.

[0192] As such, an IMD (or portion thereof) represented by a dynamically moving graphical image displayed by display unit 954 may be the distal portion of a medical electrical lead, e.g., lead 911, and/or the distal portion of a delivery tool, e.g., guide catheter 940. The methods for determining and displaying a dynamically moving graphical image of an IMD along with quantitative and/or qualitative positional information and/or dislodgment risk information as described above in conjunction with FIGs. 8-18, with reference to example IMDs 14 and 14’, may be applied to elongated IMDs such as medical electrical leads, catheters or other delivery devices.

[0193] Further disclosed herein is the subject matter of the following examples:

[0194] Example 1. A medical device system including processing circuitry configured to receive a first orientation signal that is a three dimensional signal responsive to changes in a position of an implantable medical device relative to a first reference vector. The processing circuitry may be further configured to, for each of a plurality of time points, compute an angular position of the implantable medical device relative to the first reference vector from the first orientation signal. The processing circuitry may be further configured to, for each of the computed angular positions, determine a corresponding directional difference to the angular position from a preceding angular position computed for a preceding time point of the plurality of time points. The medical device system may further include a display unit configured to display a graphic image of the implantable medical device in a starting position relative to a local coordinate system and dynamically adjust the graphic image of the implantable medical device from the starting position to the angular positions computed consecutively for the plurality of time points by rotating the graphic image of the implantable medical device between each of the consecutively computed angular positions in a clockwise or counterclockwise direction according to each of the respective corresponding directional differences.

[0195] Example 2. The medical device system of example 1 wherein the processing circuitry is further configured to, for each of the plurality of time points, compute the angular position by computing from the first orientation signal at least a pitch angle between a longitudinal axis of the implantable medical device and an axis of the local coordinate system and determine the corresponding directional difference by determining whether the pitch angle is increased or decreased from a preceding time point of the plurality of time points. The display unit is further configured to dynamically adjust the graphic image of the implantable medical device byrotating the graphic image of the implantable medical device in a clockwise or counterclockwise direction from a current pitch angle to a next pitch angle of the consecutively computed pitch angles according to the corresponding directional difference being a pitch angle increase or a pitch angle decrease.

[0196] Example 3. The medical device system of example 2 further comprising a memory- configured to store a pitch angle range. The processing circuitry' may be further configured to compare at least one of the computed pitch angles to the stored pitch angle range.

The display unit may be further configured to display a user feedback signal indicating when at least one of the computed pitch angles is in the stored pitch angle range.

[0197] Example 4. The medical device system of any' one of examples 1 — 3 wherein the processing circuitry' is further configured to, for each of the plurality' of time points, compute the angular position by computing from the first orientation signal at least a roll angle and determine the corresponding directional difference by determining whether the roll angle increases or decreases from a most recent preceding time point of the plurality of time points. The display unit may be further configured to dynamically adjust the image of the implantable medical device to the consecutively computed roll angles by rotating the image of the implantable medical device about the longitudinal axis of the implantable medical device in a clockwise or counterclockwise direction from a current roll angle to a next roll angle of the consecutively computed roll angles according to the corresponding directional difference being a roll angle increase or a roll angle decrease.

[0198] Example 5. The medical device system of example 4 wherein the processing circuitry is further configured to determine a total turn count from the consecutively determined roll angles. The display unit may be further configured to display the total turn count.

[0199] Example 6. The medical device system of example 5 further comprising a memory configured to store a turn count range and the processing circuitry is further configured to compare the total turn count to the turn count range. The display unit may be further configured to display a user prompt when the total turn count is outside the turn count range.

[0200] Example 7. The medical device system of any one of examples 4 — 6 wherein the processing circuitry is further configured to receive a tissue contact confirmation signal; and initialize the turn count to zero in response to receiving the tissue contact confirmation signal. [0201] Example 8. The medical device system of any one of examples 1 — 7 wherein the processing circuitry' is further configured to receive a second orientation signal that is a three dimensional signal responsive to changes in the position of the implantable medical device relative to a second reference vector, the second reference vector being orthogonal to the first reference vector. The processing circuit may, for at least one of the plurality of time points, compute the angular position by computing from at least the second orientation signal a yaw angle of rotation about an axis of the local coordinate system, the axis being parallel to the first reference vector. The display unit may be further configured to adjust the image of the implantable medical device to the yaw angle of rotation about the axis of the local coordinate system.

[0202] Example 9. The medical device system of example 8 wherein the processing circuitry is further configured to receive the first orientation signal as an acceleration signal responsive to changes in the position of the implantable medical device relative to the first reference vector being gravity and receive the second orientation signal as a magnetometer signal responsive to changes in the position of the implantable medical device relative to the second reference vector that is orthogonal to gravity.

[0203] Example 10. The medical device system of example 8 wherein the processing circuitry’ is further configured to receive a signal confirming alignment of the longitudinal axis of the implantable medical device orthogonal to gravity, receive the first orientation signal as an acceleration signal responsive to changes in the position of the implantable medical device relative to the first reference vector being gravity and receive the second orientation signal as a gyroscope signal responsive to changes in the position of the implantable medical device relative to the second reference vector that is orthogonal to gravity' and aligned with the longitudinal axis of the implantable medical device.

[0204] Example 11. The medical device system of any one of examples 1 — 10 further comprising a memory configured to store the computed angular positions of the implantable medical device. The processing circuitry may be further configured to apply a dislodgement risk predictor machine learning model to the angular position computed for at least one of the plurality of time points. The processing circuitry- may determine, based on the applied dislodgement risk predictor machine learning model, a dislodgement risk probability. The display unit may be further configured to display the dislodgment risk probability.

[0205] Example 12. The medical device system of example 11 wherein the processing circuitry is further configured to compute the angular position of the implantable medical device for the at least one of the plurality of time points by computing at least a pitch angle and input at least the pitch angle to the dislodgement risk predictor machine learning model. The processing circuitry may be configured to determine the dislodgment risk probability by applying the dislodgement risk predictor machine learning model to at least the pitch angle.

[0206] Example 13. The medical device system of any one of examples 11 — 12 wherein the processing circuitry is further configured to determine a total turn count from the computed angular positions of the implantable medical device and input at least the total turn count to the dislodgement risk predictor machine learning model. The processing circuitry' may determine the dislodgment risk probability by applying the dislodgement risk predictor machine learning model to at least the total turn count.

[0207] Example 14. The medical device system of any one of examples 11 — 13 wherein the processing circuitry' is further configured to receive a cardiac electrical signal feature determined from a cardiac electrical signal sensed by the implantable medical device, input at least the cardiac electrical signal feature to the dislodgement risk predictor machine learning model and determine the dislodgment risk probability' by applying the dislodgement risk predictor machine learning model to the computed angular position and the cardiac electrical signal feature.

[0208] Example 15. The medical device system of any one of examples 11 — 14 wherein the processing circuitry is further configured to receive at least one of a pacing capture threshold or an impedance measurement from the implantable medical device and input at least one of the pacing capture threshold or the impedance measurement to the dislodgement risk predictor machine learning model. The processing circuitry may determine the dislodgment risk probability by applying the dislodgement risk predictor machine learning model to the computed angular position and at least one of the capture threshold or the impedance measurement.

[0209] Example 16. The medical device system of any one of examples 1 — 15 further comprising the implantable medical device, the implantable medical device having a longitudinal axis. The medical device system further comprising an orientation sensor configured to sense the first orientation signal that is responsive to changes in position of the implantable medical device relative to the first reference vector and wherein the orientation sensor is configured to sense the first orientation signal by: sensing a first axis signal by a first sensor element along a first sensor axis of the orientation sensor that is orthogonal to the longitudinal axis of the implantable medical device; sensing a second axis signal by a second sensor element along a second sensor axis of the orientation sensor that is parallel to the longitudinal axis of the implantable medical device; and sensing a third axis signal by a third sensor element along a third sensor axis of the orientation sensor that is orthogonal to the longitudinal axis and orthogonal to the first sensor axis.

[0210] Example 17. The medical device system of any one of examples 1 — 16 further comprising a communication circuit configured to transmit the first orientation signal for receipt by the processing circuitry.

[0211] Example 18. The medical device system of any one of examples 1 — 17 wherein the implantable medical device further comprises the processing circuitry.

[0212] Example 19. The medical device system of any one of examples 1 — 17 further comprising an external device comprising the processing circuitry and the display unit. [0213] Example 20. The medical device system of any one of examples 1 — 19 further comprising a user interface. The processing circuitry may be further configured to determine that a computed angular position for at least one of the plurality of time points corresponds to a recommended implant position of the implantable medical device relative to the first reference vector. The user interface may be configured to provide a qualitative user feedback signal indicating when the computed angular position corresponds to the recommended implant position.

[0214] Example 21. The medical device system of any one of examples 1 — 20 further comprising an orientation sensor for sensing the first orientation signal, the orientation sensor comprising at least one of an accelerometer, a gyroscope or a magnetometer.

[0215] Example 22. A method comprising receiving a first orientation signal that is a three dimensional signal responsive to changes in a position of an implantable medical device relative to a first reference vector. The method includes, for each of a plurality of time points, computing an angular position of the implantable medical device relative to the first reference vector from the first orientation signal. The method may further include, for each of the computed angular positions, determining a corresponding directional difference to the angular position from a preceding angular position computed for a preceding time point of the plurality of time points. The method may include displaying a graphic image of the implantable medical device in a starting position relative to a local coordinate system. The method may include dynamically adjusting the graphic image of the implantable medical device from the starting position to the angular positions computed consecutively for the plurality of time points by rotating the graphic image of the implantable medical device between each of the consecutively computed angular positions in a clockwise or counterclockwise direction according to each of the respective corresponding directional differences.

[0216] Example 23. The method of example 22 further comprising, for each of the plurality of time points, computing the angular position by computing from the first orientation signal at least a pitch angle between a longitudinal axis of the implantable medical device and an axis of the local coordinate system and determining the corresponding directional difference by determining whether the pitch angle is increased or decreased from a preceding time point of the plurality of time points. The method may include dynamically adjusting the graphic image of the implantable medical device to the consecutively computed angular positions by rotating the graphic image of the implantable medical device in a clockwise or counterclockwise direction from a current pitch angle to a next pitch angle of the consecutively computed pitch angles according to the corresponding directional difference being a pitch angle increase or a pitch angle decrease.

[0217] Example 24. The method of example 23 further comprising storing a pitch angle range, comparing at least one of the computed pitch angles to the stored pitch angle range and displaying a user feedback signal indicating when at least one of the computed pitch angles is in the stored pitch angle range.

[0218] Example 25. The method of any one of examples 22 — 24 further comprising, for each of the plurality of time points computing the angular position by computing from the first orientation signal at least a roll angle and determining the corresponding directional difference by determining whether the roll angle increases or decreases from a most recent preceding time point of the plurality of time points, dynamically adjusting the image of the implantable medical device to the consecutively computed roll angles by rotating the image of the implantable medical device about the longitudinal axis of the implantable medical device in a clockwise or counterclockwise direction from a current roll angle to a next roll angle of the consecutively computed roll angles according to the corresponding directional difference being a roll angle increase or a roll angle decrease.

[0219] Example 26. The method of example 25 further comprising determining a total turn count from the consecutively determined roll angles and displaying the total turn count.

[0220] Example 27. The method of example 26 further comprising storing a turn count range, comparing the total turn count to the turn count range and displaying a user prompt when the total turn count is outside the turn count range.

[0221] Example 28. The method of any one of examples 25 — 27 further comprising receiving a tissue contact confirmation signal and initializing the turn count to zero in response to receiving the tissue contact confirmation signal.

[0222] Example 29. The method of any one of examples 22 — 28 further comprising receiving a second orientation signal that is a three dimensional signal responsive to changes in the position of the implantable medical device relative to a second reference vector, the second reference vector being orthogonal to the first reference vector. The method may include, for at least one of the plurality of time points, computing the angular position by computing from at least the second orientation sensor signal a yaw angle of rotation about an axis of the local coordinate system, the axis being parallel to the first reference vector. The method may include adjusting the image of the implantable medical device to the yaw angle of rotation about the axis of the local coordinate system.

[0223] Example 30. The method of example 29 further comprising providing the second reference vector as a magnetic field vector orthogonal to gravity', sensing the first orientation signal as an acceleration signal responsive to changes in the position of the implantable medical device relative to the first reference vector being gravity' and sensing the second orientation signal as a magnetometer signal responsive to changes in the position of the implantable medical device relative to the second reference vector that is orthogonal to gravity'.

[0224] Example 31. The method of example 29 further comprising receiving a signal confirming alignment of the longitudinal axis of the implantable medical device orthogonal to gravity', receiving the first orientation signal as an acceleration signal responsive to changes in the position of the implantable medical device relative to the first reference vector being gravity' and receiving the second orientation signal as a gyroscope signal responsive to changes in the position of the implantable medical device relative to the second reference vector that is orthogonal to gravity⁷ and aligned with the longitudinal axis of the implantable medical device. [0225] Example 32. The method of any one of examples 22 — 31 further comprising storing the computed angular positions of the implantable medical device and applying a dislodgement risk predictor machine learning model to the angular position computed for at least one of the plurality of time points. The method may include determining, based on the applied dislodgement risk predictor machine learning model, a dislodgement risk probability and displaying the dislodgment risk probability.

[0226] Example 33. The method of example 32 further comprising computing the angular position of the implantable medical device for the at least one of the plurality' of time points by computing at least a pitch angle, inputting at least the pitch angle to the dislodgement risk predictor machine learning model and determining the dislodgment risk probability by applying the dislodgement risk predictor machine learning model to at least the pitch angle.

[0227] Example 34. The method of any one of examples 32 — 33 further comprising determining a total turn count from the computed angular positions of the implantable medical device, inputting at least the total turn count to the dislodgement risk predictor machine learning model and determining the dislodgment risk probability by applying the dislodgement risk predictor machine learning model to at least the total turn count.

[0228] Example 35. The method of any one of examples 32 — 34 further comprising receiving a cardiac electrical signal feature determined from a cardiac electrical signal sensed by the implantable medical device and inputting at least the cardiac electrical signal feature to the dislodgement risk predictor machine learning model. The method may include determining the dislodgment risk probability by applying the dislodgement risk predictor machine learning model to at least the computed angular position and the cardiac electrical signal feature.

[0229] Example 36. The method of any one of examples 33 — 35 further comprising receiving at least one of a pacing capture threshold or an impedance measurement from the implantable medical device and inputting at least one of the pacing capture threshold or the impedance measurement to the dislodgement risk predictor machine learning model. The method may further include determining the dislodgment risk probability by applying the dislodgement risk predictor machine learning model to at least the computed angular position and at least one of the capture threshold or the impedance measurement.

[0230] Example 37. The method of any one of examples 22 — 36 further comprising sensing, by an orientation sensor, the first orientation signal that is responsive to changes in position of the implantable medical device relative to the first reference vector, wherein sensing the first orientation signal comprises: sensing a first axis signal by a first sensor element along a first sensor axis of the orientation sensor that is orthogonal to a longitudinal axis of the implantable medical device; sensing a second axis signal by a second sensor element along a second sensor axis of the orientation sensor that is parallel to the longitudinal axis of the implantable medical device and sensing a third axis signal by a third sensor element along a third sensor axis of the orientation sensor that is orthogonal to the longitudinal axis and orthogonal to the first sensor axis.

[0231] Example 38. The method of example 37 further comprising transmitting the first orientation signal for receipt by the processing circuitry.

[0232] Example 39. The method of any one of examples 22 — 38 further comprising determining that a computed angular position for at least one of the plurality of time points corresponds to a recommended implant position of the implantable medical device relative to the first reference vector. The method may further include providing a qualitative user feedback signal indicating when the computed angular position corresponds to the recommended implant position.

[0233] Example 40. The method of any one of examples 22 — 39 further comprising sensing the first orientation signal by at least one of an accelerometer, a gyroscope or a magnetometer.

[0234] Example 41. A non-transitory computer readable medium storing instructions which, when executed by processing circuitry of a medical device system, cause the medical device system to receive an orientation signal that is a three dimensional signal responsive to changes in a position of an implantable medical device relative to a reference vector. The instructions may further cause the medical device system to, for each of a plurality of time points, compute an angular position of the implantable medical device relative to the first reference vector from the orientation signal and determine a corresponding directional difference to the angular position from a preceding angular position computed for a preceding time point of the plurality of time points. The instructions may further cause the medical device system to display a graphic image of the implantable medical device in a starting position relative to a local coordinate system and dynamically adjust the graphic image of the implantable medical device from the starting position to the angular positions computed consecutively for the plurality of time points by rotating the graphic image of the implantable medical device between each of the consecutively computed angular positions in a clockwise or counterclockwise direction according to each of the respective corresponding directional differences.

[0235] It should be understood that, depending on the example, certain acts or events of any of the methods described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the method). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially. In addition, while certain aspects of this disclosure are described as being performed by a single circuit or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or circuits associated with, for example, a medical device system.

[0236] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media (e.g.. RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0237] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPLAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term ‘‘processor,” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0238] Thus, a medical device system has been presented in the foregoing description with reference to specific examples. It is to be understood that various aspects disclosed herein may be combined in different combinations than the specific combinations presented in the accompanying drawings. It is appreciated that various modifications to the referenced examples may be made without departing from the scope of the disclosure and the following claims.

Claims

WHAT IS CLAIMED IS:

1 . A medical device system comprising: processing circuitry configured to: receive a first orientation signal that is a three dimensional signal responsive to changes in a position of an implantable medical device relative to a first reference vector; for each of a plurality of time points: compute an angular position of the implantable medical device relative to the first reference vector from the first orientation signal; and determine a corresponding directional difference to the angular position from a preceding angular position computed for a preceding time point of the plurality of time points; and a display unit configured to: display a graphic image of the implantable medical device in a starting position relative to a local coordinate system; dynamically adjust the graphic image of the implantable medical device from the starting position to the angular positions computed consecutively for the plurality of time points by rotating the graphic image of the implantable medical device between each of the consecutively computed angular positions in a clockwise or counterclockwise direction according to each of the respective corresponding directional differences.

2. The medical device system of claim 1 wherein the processing circuitry is further configured to, for each of the plurality of time points: compute the angular position by computing from the first orientation signal at least a pitch angle between a longitudinal axis of the implantable medical device and an axis of the local coordinate system; and determine the corresponding directional difference by determining whether the pitch angle is increased or decreased from a preceding time point of the plurality of time points; the display unit is further configured to dynamically adjust the graphic image of the implantable medical device by rotating the graphic image of the implantable medical device in a clockwise or counterclockwise direction from a current pitch angle to a next pitch angle of the consecutively computed pitch angles according to the corresponding directional difference being a pitch angle increase or a pitch angle decrease.

3. The medical device system of claim 2 further comprising a memory configured to store a pitch angle range; and wherein: the processing circuitry' is further configured to compare at least one of the computed pitch angles to the stored pitch angle range; and the display unit is further configured to display a user feedback signal indicating when at least one of the computed pitch angles is in the stored pitch angle range.

4. The medical device system of any one of examples 1 — 3 wherein: the processing circuitry is further configured to, for each of the plurality of time points: compute the angular position by computing from the first orientation signal at least a roll angle; and determine the corresponding directional difference by determining whether the roll angle increases or decreases from a most recent preceding time point of the plurality of time points; the display unit is further configured to dynamically adjust the image of the implantable medical device to the consecutively computed roll angles by rotating the image of the implantable medical device about the longitudinal axis of the implantable medical device in a clockwise or counterclockwise direction from a current roll angle to a next roll angle of the consecutively computed roll angles according to the corresponding directional difference being a roll angle increase or a roll angle decrease.

5. The medical device system of claim 4 wherein: the processing circuitry’ is further configured to determine a total turn count from the consecutively determined roll angles; and the display unit being further configured to display the total turn count.

6. The medical device system of claim 5 further comprising a memory configured to store a turn count range, and wherein: the processing circuitry is further configured to compare the total turn count to the turn count range; and the display unit being further configured to display a user prompt when the total turn count is outside the turn count range.

7. The medical device system of any one of claims 4 — 6 wherein the processing circuitry is further configured to: receive a tissue contact confirmation signal; and initialize the turn count to zero in response to receiving the tissue contact confirmation signal.

8. The medical device system of any one of claims 1 — 7 wherein: the processing circuitry is further configured to: receive a second orientation signal that is a three dimensional signal responsive to changes in the position of the implantable medical device relative to a second reference vector, the second reference vector being orthogonal to the first reference vector; for at least one of the plurality of time points, compute the angular position by computing from at least the second orientation signal a yaw angle of rotation about an axis of the local coordinate system, the axis being parallel to the first reference vector; and the display unit is further configured to adjust the image of the implantable medical device to the yaw angle of rotation about the axis of the local coordinate system.

9. The medical device system of any one of claims 1 — 8 further compnsing a memory configured to store the computed angular positions of the implantable medical device; and wherein: the processing circuitry is further configured to: apply a dislodgement risk predictor machine learning model to the angular position computed for at least one of the plurality of time points; and determine, based on the applied dislodgement risk predictor machine learning model, a dislodgement risk probability; and the display unit is further configured to display the dislodgment risk probability.

10. The medical device system of claim 9 wherein the processing circuitry is further configured to: receive at least one of a pacing capture threshold, an impedance measurement or a cardiac electrical signal feature determined from a cardiac electrical signal sensed by the implantable medical device; input at least one of the pacing capture threshold, the impedance measurement or the cardiac electrical signal feature to the dislodgement risk predictor machine learning model; and determine the dislodgment risk probability by applying the dislodgement risk predictor machine learning model to the computed angular position and the cardiac electrical signal feature.

1 1. The medical device system of any one of claims 1 — 10 further comprising the implantable medical device, the implantable medical device having a longitudinal axis and comprising: an orientation sensor configured to sense the first orientation signal that is responsive to changes in position of the implantable medical device relative to the first reference vector; and wherein the orientation sensor is configured to sense the first orientation signal by: sensing a first axis signal by a first sensor element along a first sensor axis of the orientation sensor that is orthogonal to the longitudinal axis of the implantable medical device; sensing a second axis signal by a second sensor element along a second sensor axis of the orientation sensor that is parallel to the longitudinal axis of the implantable medical device; and sensing a third axis signal by a third sensor element along a third sensor axis of the orientation sensor that is orthogonal to the longitudinal axis and orthogonal to the first sensor axis.

12. The medical device system of claim 11 wherein the orientation sensor for sensing the first orientation signal comprises at least one of an accelerometer, a gyroscope or a magnetometer.

13. The medical device system of any one of claims 11 — 12 wherein the implantable medical device further comprises a communication circuit configured to transmit the first orientation signal for receipt by the processing circuitry.

14. The medical device system of any one of claims 1 — 13 further comprising an external device comprising the processing circuitry and the display unit.

15. The medical device system of any one of claims 1 — 14 further comprising a user interface, wherein: the processing circuitry is further configured to determine that a computed angular position for at least one of the plurality of time points corresponds to a recommended implant position of the implantable medical device relative to the first reference vector; and the user interface being configured to provide a qualitative user feedback signal indicating when the computed angular position corresponds to the recommended implant position.