WO2025158232A1

WO2025158232A1 - Implantable medical device to detect health event based on cardiac activity

Info

Publication number: WO2025158232A1
Application number: PCT/IB2025/050290
Authority: WO
Inventors: James R. LIBBEY; Kaileigh E. HAYDEN; Maureen E. Lybarger; Todd J. Sheldon; Joshua J. BLAUER; Ronson Lok YONG
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 2024-01-23
Filing date: 2025-01-10
Publication date: 2025-07-31
Anticipated expiration: 2026-07-23

Abstract

An example system includes an implantable medical device (IMD) configured to be implanted in a patient, the IMD comprising a motion sensor configured to generate a motion signal based on cardiac motion over a period of time; and processing circuitry configured to: determine one or more cardiac activity counts of a heart of the patient based on the motion signal; determine an indication of heart failure based on the one or more cardiac activity counts; and output information pertaining to the indication of heart failure to a device or network.

Description

IMPLANTABLE MEDICAL DEVICE TO DETECT HEALTH EVENT BASED ON

CARDIAC ACTIVITY

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63/624,023, filed January 23, 2024, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The disclosure relates to medical devices, and more particularly to the detection of a health event, such as onset or progression of heart failure, by the medical devices.

BACKGROUND

[0003] An implantable pacemaker may deliver pacing pulses to a patient’s heart and monitor conditions of the patient’s heart. In some examples, the implantable pacemaker comprises a pulse generator and one or more electrical leads. The pulse generator may, for example, be implanted in a small pocket in the patient’s chest. The electrical leads may be coupled to the pulse generator, which may contain circuitry that generates pacing pulses and/or senses cardiac electrical activity. The electrical leads may extend from the pulse generator to a target site (e.g., an atrium and/or a ventricle) such that electrodes at the distal ends of the electrical leads are positioned at the target site. The pulse generator may provide electrical stimulation to the target site and/or monitor cardiac electrical activity at the target site via the electrodes.

[0004] Other implantable pacemakers are configured to be implanted entirely within a chamber of the heart. Such pacemakers may be referred to as intracardiac pacing devices or leadless pacing devices, and may include one or more electrodes on their outer housings to deliver therapeutic electrical signals and/or sense intrinsic depolarizations of the heart. Such pacemakers may be positioned within or outside of the heart and, in some examples, may be anchored to a wall of the heart via a fixation mechanism.

SUMMARY

[0005] In general, this disclosure describes example techniques related to the detection of patients progressing into HF without using an “exercise test,” which typically relies on data of a patient collected while the patient is exercising or at a paced exercise mode. For example, processing circuitry, such as processing circuitry of an implantable medical device (IMD), may determine cardiac activity counts, e.g., when a patient is at rest reflecting the state of the patient at rest. Cardiac activity counts may correspond to a degree of heart motion and/or an amount of energy used by a heart. The processing circuitry may determine cardiac activity counts based on an accelerometer signal or other motion signal. The processing circuitry may determine and/or predict heart failure (HF) based on the cardiac activity counts. In some examples, the techniques of this disclosure for determining/predicting HF need not include identification of distinct heart sounds through signal processing, which may reduce processing power consumption and/or increase battery life of an IMD configured to determine/predict HF.

[0006] In some examples, processing circuitry, such as processing circuitry of an IMD, may determine a workload of heart of a patient using a sensor, such as a plurality of electrodes and/or a motion sensor. The processing circuitry may determine a first setpoint based on a workload of a heart during a first period of time, determine a second setpoint based on a workload of a heart during a second period of time, and determine a value of cardiac motion of the heart based, at least in part, on the first setpoint and the second setpoint. The processing circuitry may determine and/or predict HF based on the determined value of cardiac motion. As a patient progresses in HF, a patient may become less active overall, so despite some potential confounding processing circuitry may determine and/or predict HF based on the cardiac motion determined via the change in value of setpoints.

[0007] In one example, this disclosure describes a system comprising: an implantable medical device (IMD) configured to be implanted in a patient, the IMD comprising a motion sensor configured to generate a motion signal based on cardiac motion over a period of time; and processing circuitry configured to: determine one or more cardiac activity counts of a heart of the patient based on the motion signal; determine an indication of heart failure based on the one or more cardiac activity counts; and output information pertaining to the indication of heart failure to a device or network.

[0008] In another example, this disclosure describes a system comprising: an implantable medical device comprising: a sensor configured to detect a signal indicative of a workload of a heart of a patient; and therapy generation circuitry configured to deliver cardiac pacing to the heart; and processing circuitry configured to: determine a value of a parameter indicative of workload of the heart of the patient based on the detected signal; control the therapy generation circuitry to deliver the cardiac pacing at a pacing rate based on the value of the parameter and a predetermined relationship between values of the parameter and cardiac pacing rates; determine a first setpoint for the predetermined relationship based on a value of a parameter indicative of a workload of the heart during a first period of time; determine a second setpoint for the relationship based on a value of a parameter indicative of a workload of the heart during a second period of time, the second period of time being after the first period of time; determine an indication of heart failure based, at least in part, on the first setpoint and the second setpoint; and output information pertaining to the indication of heart failure to a device or network.

[0009] In another example, this disclosure describes a method comprising: determining one or more cardiac activity counts of a heart of a patient based on a motion signal based on cardiac motion; determining an indication of heart failure based on the one or more cardiac activity counts; and outputting information pertaining to the indication of heart failure to a device or network.

[0010] In another example, this disclosure describes a method comprising: determining a value of a parameter indicative of a workload of a heart of a patient based on a sensed signal via a sensor; determining a first setpoint based on a value of a parameter indicative of a workload of the heart during a first period of time; determining a second setpoint based on a value of a parameter indicative of a workload of the heart during a second period of time, the second period of time being after the first period of time; determining an indication of heart failure based, at least in part, on the first setpoint and the second setpoint; and outputting information pertaining to the indication of heart failure to a device or network.

[0011] This summary is intended to provide an overview of the subject matter described in this disclosure. It is not intended to provide an exclusive or exhaustive explanation of the methods and systems described in detail within the accompanying drawings and description below. The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below.

BRIEF DESCRIPTION OF DRAWINGS [0012] The details of one or more examples of this disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of this disclosure will be apparent from the description and drawings, and from the claims.

[0013] FIG. 1 is a conceptual diagram illustrating an example pacing device implanted within a patient.

[0014] FIG. 2 is a conceptual illustration of an example configuration of a pacing device, in accordance with some examples of the current disclosure.

[0015] FIG. 3A is a perspective drawing illustrating another example configuration of a pacing device, in accordance with some examples of the current disclosure.

[0016] FIG. 3B is a perspective drawing illustrating another example configuration of a pacing device, in accordance with some examples of the current disclosure.

[0017] FIG. 4A is a conceptual block diagram of an example IMD, which may be implemented in or as the pacing device of other examples, in accordance with some examples of the current disclosure.

[0018] FIG. 4B is an example flow diagram illustrating an example of determining one or more cardiac activity counts, in accordance with some examples of the current disclosure.

[0019] FIG. 4C is an example graph illustrating an example of determining one or more setpoints, in accordance with some examples of the current disclosure.

[0020] FIG. 4D are example graphs illustrating an example rate histogram and example target histogram, in accordance with some examples of the current disclosure. [0021] FIG. 5 is a functional block diagram illustrating an example configuration of the external device of FIGS. 1 and 6.

[0022] FIG. 6 is a block diagram illustrating an example system that includes an external device, such as a server, and one or more computing devices that are coupled to the IMD and external device via a network, in accordance with some examples of the current disclosure.

[0023] FIG. 7 is a flow diagram illustrating an example process executable by a system, in accordance with some examples of the current disclosure.

[0024] FIG. 8 is a flow diagram illustrating an example process executable by a system, in accordance with some examples of the current disclosure. [0025] FIG. 9 is a flow diagram illustrating an example process executable by a system, in accordance with some examples of the current disclosure.

DETAILED DESCRIPTION

[0026] Pacing provides a life preserving therapy for patients. However, patients requiring pacing have an increased risk of experiencing an onset of heart failure (HF) or having worsening HF. Early detection of changes in the tissue properties, such as the onset of HF or worsening HF, would permit intervention before significant damage is done. [0027] A variety of types of medical devices sense cardiac motion and cardiac workload of a patient. An IMD may include an accelerometer or other motion sensor configured to sense accelerometer signals from which processing circuitry of a system including the IMD may determine cardiac activity counts to determine an indication of HF. In some examples, an IMD may include a motion sensor and/or a plurality of electrodes configured to detect a respective signal indicative of a workload of a heart to determine an indication of HF. Example IMDs that may include pacemakers and implantable cardioverter-defibrillators, which may be coupled to intravascular or extravascular leads, as well as pacemakers with housings configured for implantation within the heart, which may be leadless. An example of a pacemaker configured for intracardiac implantation is the Micra™ Transcatheter Pacing System, available from Medtronic, Inc.

[0028] Some IMDs that do not provide therapy, e.g., implantable patient monitors, may be configured to sense the cardiac motion and/or cardiac electrical activity signals described herein. Two examples of such IMDs are the Reveal LINQ™ and LINQ II™ Insertable Cardiac Monitors (ICMs), available from Medtronic, Inc., which may be inserted subcutaneously. Such IMDs may facilitate relatively longer-term monitoring of patients during normal daily activities, and may periodically transmit collected data to a network service, such as the Medtronic Carelink™ Network.

[0029] In general, this disclosure describes example techniques for determining the HF state of patients, which may enable effective detection of patients progressing into HF without using an “exercise test” that relies on data of a patient while the patient is exercising or at a paced exercise mode. As patients progress in HF, the heart gets weaker, which may be seen in decreasing cardiac motion and/or decreasing energy used by the heart during resting heart beats. The techniques of this disclosure include sensing signals that enable the system to identify decreasing cardiac motion and/or decreasing energy used by the heart during resting heart beats. An IMD or other sensing device may be configured to sense such signals continuously, e.g., on a periodic and/or triggered basis, without requiring user intervention.

[0030] Some of the techniques described herein may use an accelerometer signal or other motion or vibration sensor signal (described herein primarily in the context of an accelerometer) to determine cardiac activity counts, which may correspond to an amount of energy used by a heart during a time period, such as at rest. The processing circuitry of a system may use the cardiac activity counts to determine and/or predict HF. In some examples, the techniques of this disclosure do not include identification of distinct heart sounds through signal processing, and thus may determine and/or predict HF in a manner that reduces processing power and/or increases battery life of an IMD and/or other devices of a medical system configured to determine/predict HF.

[0031] A cardiac pacing rate function is a function that allows processing circuitry of a cardiac pacemaker, or other device of a system including a pacemaker, to determine a rate for cardiac pacing to be delivered to a patient, (e.g., an escape interval value for cardiac pacing) based on a current activity level of the patient. The processing circuitry may determine the activity level based on an accelerometer or other motion sensor, or based on another sensed physiological signal indicative of exertion of the patient, such as respiration. A cardiac pacing rate function may include a combination of linear and/or non-linear functions (e.g., multiple linear functions having different slopes) with set points between the functions.

[0032] Some of the techniques described herein may use a sensor, such as a plurality of electrodes and/or a motion sensor, to determine a first activity of daily living (ADL), or other cardiac pacing rate function setpoint based on a workload of a heart during a first period of time, determine a second ADL or other cardiac pacing rate function setpoint based on a workload of a heart during a second period of time, and determine a value of cardiac motion of the heart based, at least in part, on the first setpoint and the second setpoint. Processing circuitry may use the determined value of cardiac motion to determine and/or predict HF. As a patient progresses in HF, they may become less active overall, so despite some potential confounding, the cardiac pacing rate function setpoints, such as the first setpoint and the second setpoint, may still be used as a composite of the cardiac motion and activity level to determine and/or predict HF.

[0033] FIG. 1 is a conceptual diagram illustrating an example pacing device 12 implanted within a patient 14. Pacing device 12 is an example of an IMD that may be fixed to heart 16 to provide electrical signals via electrodes to heart 16 and facilitate detection of motion of heart 16 as described herein. Pacing device 12 may be, for example, an implantable leadless pacing device that is configured for implantation entirely within one of the chambers of heart 16, and that provides electrical signals to heart 16 via electrodes carried on the housing of pacing device 12.

[0034] Pacing device 12 is generally described as being implanted within a chamber of heart 16 as an intracardiac pacing device. In other examples that are consistent with aspects of this disclosure, pacing device 12 may be affixed to an external surface of heart 16, such that pacing device 12 is disposed outside of heart 16 but can pace a desired chamber. In one example, pacing device 12 is affixed to an external surface of heart 16, and one or more components of pacing device 12 may be in contact with the epicardium of heart 16. Pacing device 12 may be affixed to a wall of a ventricle of heart 16, or other chamber, via one or more fixation elements (e.g., tines, helix, etc.) that penetrate the tissue. These fixation elements may secure pacing device 12 to the cardiac tissue and retain an electrode (e.g., a cathode or an anode) in contact with the cardiac tissue. Pacing device 12 may be implanted at or proximate to the apex of the heart. In other examples, a pacing device may be implanted at other ventricular locations, e.g., on the free-wall or septum, an atrial location, such as near the Triangle of Koch, or any location on or within heart 16. Being fixed to heart 16 may facilitate detection of motion of the heart by pacing device 12.

[0035] FIG. 2 is a conceptual illustration of an example configuration of pacing device 12. Pacing device 12 is configured to be implanted within a chamber of a heart of a patient, e.g., to monitor electrical activity of the heart and/or provide electrical therapy to the heart. In the example shown in FIG. 2, pacing device 12 includes outer housing 150, a plurality of fixation tines 110 and electrodes 100 and 160.

[0036] Outer housing 150 has a size and form factor that allows pacing device 12 to be entirely implanted within a chamber of a heart of a patient. In some examples, outer housing 150 may have a cylindrical (e.g., pill-shaped or capsule-shaped) form factor. Pacing device 12 may include a fixation mechanism configured to fix pacing device 12 to cardiac tissue. For example, in the example shown in FIG. 2, pacing device 12 includes fixation tines 110 extending from housing 150 and configured to engage with cardiac tissue to substantially fix a position of housing 150 within the chamber of the heart 16. Fixation tines 110 are configured to anchor housing 150 to the cardiac tissue such that pacing device 12 moves along with the cardiac tissue during cardiac contractions. Fixation tines 110 may be fabricated from any suitable material, such as a shape memory material (e.g., Nitinol). Although pacing device 12 includes a plurality of fixation tines 110 that are configured to anchor pacing device 12 to cardiac tissue in a chamber of a heart, in other examples, pacing device 12 may be fixed to cardiac tissue using other types of fixation mechanisms, such as, but not limited to, barbs, coils, and the like.

[0037] Housing 150, also referred to as an elongated housing, houses electronic components of pacing device 12, e.g., sensing circuitry for sensing cardiac electrical activity via electrodes 100 and 160 and therapy generation circuitry for delivering electrical stimulation therapy via electrodes 100 and 160. Electronic components may include any discrete and/or integrated electronic circuit components that implement analog and/or digital circuits capable of producing the functions attributed to pacing device 12 described herein. In some examples, housing 150 may also house components for sensing other physiological parameters, such as acceleration, pressure, sound, and/or impedance. [0038] Additionally, housing 150 may also house a memory that includes instructions that, when executed by processing circuitry housed within housing 150, cause pacing device 12 to perform various functions attributed to pacing device 12 herein. In some examples, housing 150 may house communication circuitry that enables pacing device 12 to communicate with other electronic devices, such as a medical device programmer or other external device 24. In some examples, housing 150 may house an antenna for wireless communication. Housing 150 may also house a power source, such as a battery. Housing 150 can be hermetically or near-hermetically sealed in order to help prevent fluid ingress into housing 150.

[0039] Pacing device 12 is configured to sense electrical activity of the heart and deliver electrical stimulation to the heart via electrodes 100 and 160. Electrode 100 and/or electrode 160 may be mechanically connected to housing 150. As another example, electrode 100 and/or electrode 160 may be defined by an outer portion of housing 150 that is electrically conductive. For example, electrode 160 may be defined by a conductive portion of housing 150. In some examples, electrode 160 may serve as an anode and/or a return electrode, and electrode 100 may serve as a cathode, configured to electrically contact cardiac tissue and deliver pacing pulses thereto. Pacing device 12 may be equipped with multiple cathode electrodes. Such multiple cathode electrodes can be configured to electrically contact and deliver pacing pulses to cardiac tissue of a single heart chamber, or cardiac tissue of multiple heart chambers. In some such embodiments, the multiple cathode electrodes may be configured to electrically contact and deliver pacing pulses to cardiac tissue of different heart chambers. For example, one cathode electrode may be configured to electrically contact and deliver pacing pulses to atrial tissue, and another cathode electrode may be configured to electrically contact and deliver pacing pulses to ventricular tissue.

[0040] In the example of FIG. 2, housing 150 includes a first portion 152A and a second portion 152B. Portion 152B may, in some examples, define at least part of a power source case that houses a power source (e.g., a battery) of pacing device 12. The power source case may house a power source (e.g., a battery) of pacing device 12. In some examples, the portion 152B may include the conductive portion of housing that forms electrode 160.

[0041] Electrodes 100 and 160 are electrically isolated from each other. Electrode 100 may be referred to as a tip electrode, and fixation tines 110 may be configured to anchor pacing device 12 to cardiac tissue such that electrode 100 maintains contact with the cardiac tissue. In some examples, a portion of housing 150 may be covered by, or formed from, an insulative material to isolate electrodes 100 and 160 from each other and/or to provide a desired size and shape for one or both of electrodes 100 and 160. Electrode 160 may be a portion of housing 150, e.g., housing portion 152B, that does not include such insulative material. Electrode 160 can be most or all of housing 150, but most of housing 150 (other than electrode 160, may be covered with an insulative coating. Additionally or alternatively, electrode 160 may be coated with materials to promote conduction. In some examples, electrode 160 may be part of a separate ring portion of housing 150 that is conductive. Electrodes 100 and 160, which may include conductive portion(s) of housing 16, may be electrically connected to at least some electronics of pacing device 12 (e.g., sensing circuitry, electrical stimulation circuitry, or both). In some examples, housing 150 may include an end cap 172, which may include a feedthrough assembly to electrically couple electrode 100 to the electronics within housing 150, while electrically isolating electrode 100 from housing 150, e.g., including electrode 160 or other conductive portions of housing 150.

[0042] In the example of FIG. 2, the proximal end of pacing device 12 includes a flange 158 that defines an opening. Flange 158 may enable medical instruments to attach to pacing device 12, e.g., for delivery and/or extraction of pacing device 12. For example, a tether that extends through a catheter inserted into heart 16 (FIG. 1) may be attached to flange 158 and/or threaded through the opening to implant or extract pacing device 12. [0043] FIG. 3A is a perspective drawing illustrating an example of a pacing device 10 to sense in and/or deliver cardiac pacing to more than one chamber of a heart. Device 10 may be implanted in the right atrium (RA) of the patient’ s heart in a target implant region, such as the triangle of Koch, in the heart of the patient with a distal end of device 10 directed toward the left ventricle (LV) of the patient’s heart. While the distal end of device 10 may be directed toward the LV, the distal end may be directed to other targets, such as interventricular septum of heart, in some examples.

[0044] Device 10 includes a housing 30 that defines a hermetically sealed internal cavity. Housing 30 extends between distal end 32 and proximal end 34. In some examples, housing can be cylindrical or substantially cylindrical but may be other shapes, e.g., prismatic or other geometric shapes. Housing 30 may include a delivery tool interface member 36, e.g., at proximal end 25, for engaging with a delivery tool during implantation of device 10.

[0045] All, substantially all, or a portion of housing 30 may function as an electrode 38, e.g., an anode, during pacing and/or sensing. In some examples, electrode 38 can circumscribe a portion of housing 30 at or near proximal end 34. Electrode 38 can fully or partially circumscribe housing 30. FIG. 3 A shows electrode 38 extending as a singular band. Electrode 38 can also include multiple segments spaced a distance apart along a longitudinal axis 40 of housing 30 and/or around a perimeter of housing 30.

[0046] In some examples, electrode 38 may be a component, such as a ring electrode, that is mounted or assembled onto housing 30. Electrode 38 may be electrically coupled to internal circuitry of device 10 via electrically-conductive housing 30 or an electrical conductor when housing 30 is a non-conductive material. In some examples, electrode 38 is located proximate to proximal end 25 of housing 30 and can be referred to as a proximal housing-based electrode. Electrode 38 can also be located at other positions along housing 30, e.g., located proximately to distal end 22 or at other positions along longitudinal axis 40.

[0047] Each of first electrode 26 and second electrode 28 extends from a first end that is fixedly attached to housing 30 at or near distal end 22, to a second end that, in the example of FIG. 3A, is not attached to housing 30 other than via the first end (e.g., is a free end). First electrode 26 includes one or more coatings configured to define a first electrically active region 44 and second electrode 28 includes one or more coatings configured to define a second electrically active region 46. In some examples, first electrically active region 44 can be more proximate to the second, e.g., distal, end of first electrode 26 than second electrically active region 46 is proximate to either end of second electrode 28. In the example of FIG. 3A, first electrically active region 44 includes the distal end of electrode 26.

[0048] In the example of FIG. 3 A, first electrode 26 takes the form of a helix. In some examples, a helix is an object having a three-dimensional shape like that of a wire wound uniformly in a single layer around a cylindrical or conical surface such that the wire would be in a straight line if the surface were unrolled into a plane. Second electrode 28 includes a ramp portion 29, which may be configured as a partial helix, e.g., a helix that does not make a full revolution around a circumference of the cylindrical or conical surface.

[0049] As illustrated in FIG. 3A, first electrode 26 may be a right-hand wound helix, and second electrode 28 may be a left-hand wound partial helix, although in other examples the handedness of the electrodes may be switched or the electrodes may have the same handedness as each other. In the example of FIG. 3A, the helix and partial helix defined by first electrode 26 and second electrode 28, respectively, have the same pitch, although they may have different pitches in other examples. In some examples, one or both of electrodes 26 and 28 may have a shape other than helical. For example, the second electrode may have a loop shape in some examples. As another example, a first electrode configured to penetrate tissue of another chamber may be configured as one or more elongate darts, barbs, or tines.

[0050] First and second electrodes 26 and 28 can also vary in size and shape in order to enhance tissue contact of first and second electrically active regions 44 and 46. For example, first and second electrodes 26 and 28 can have a round cross section or could be made with a flatter cross section (e.g., oval or rectangular) based on tissue contact specifications.

[0051] The distal end of first electrode 26 can have a conical, hemi-spherical, or slanted edge distal tip with a narrow tip diameter, e.g., less than 1 millimeter (mm), for penetrating into and through tissue layers.

[0052] The outer dimensions of first electrode 26 may be substantially straight and cylindrical, with first electrode 26 being rigid in some examples. In some examples, first and second electrodes 26 and 28 can have flexibility in lateral directions, being non-rigid to allow some flexing with heart motion. In a relaxed state, when not subjected to any external forces, first and second electrodes 26 and 28 may be configured to maintain a distance between first and second electrically active regions 44 and 46 and housing distal end 32.

[0053] The configurations of first and second electrodes 26 and 28 illustrated in FIG. 3A are merely examples. In some examples, first electrode 26 may comprise one or more darts, tines, or other structures. In some examples, second electrode 28 may comprise one or more helices, darts, tines, buttons, pads, or other structures.

[0054] In some examples, second electrode 28 or electrode 38 may be paired with first electrode 26 for sensing ventricular signals and delivering ventricular pacing pulses. In some examples, second electrode 28 may be paired with electrode 38 or first electrode 26 for sensing atrial signals and delivering pacing pulses to atrial myocardium 20 in target implant region 2. In other words, electrode 38 may be paired, at different times, with both first electrode 26 and second electrode 28 for either ventricular or atrial functionality, respectively, in some examples. In some examples, first and second electrodes 26 and 28 may be paired with each other, with different polarities, for atrial and ventricular functionality.

[0055] In some examples, second electrode 28 may be configured as an atrial cathode electrode for delivering pacing pulses to the atrial tissue at target implant region in combination with electrode 38. Second electrode 28 and electrode 38 may also be used to sense atrial P-waves for use in controlling atrial pacing pulses (delivered in the absence of a sensed P-wave) and for controlling atrial-synchronized ventricular pacing pulses delivered using first electrode 26 as a cathode and electrode 38 as the return anode.

[0056] At distal end 22, device 10 includes a distal fixation assembly 42 including first electrode 26, second electrode 28, and housing distal end 32. A distal end of first electrode 26 can be configured to rest within a ventricular myocardium of the patient, and second electrode 28 can be configured to contact an atrial endocardium of the patient. In some examples, distal fixation assembly 42 can include more or less electrodes than two electrodes. In some examples, distal fixation assembly 42 may include one or more second electrodes along housing distal end 32. For example, distal fixation assembly 42 may include three electrodes configured for atrial functionality like second electrode 28, and the three electrodes may be substantially similar or different from one another. Spacing between a plurality of second electrodes 28 may be at an equal or unequal distance. Second electrode(s) 28 may be individually selectively coupled to sensing and/or pacing circuitry enclosed by housing 30 for use as an anode with first electrode 26 or as an atrial cathode electrode, or may be electrically common and not individually selectable.

[0057] FIG. 3B is a perspective diagram illustrating an example of a pacing device 11 to sense in and/or deliver cardiac pacing to more than one chamber of a heart. Housing 202 may be formed from a conductive material including titanium or titanium alloy, stainless steel, MP35N (a non-magnetic nickel-cobalt-chromium- molybdenum alloy), platinum alloy or other bio-compatible metal or metal alloy, or other suitable conductive material. In some examples, housing 202 is formed from a non-conductive material including ceramic, glass, sapphire, silicone, polyurethane, epoxy, acetyl co-polymer plastics, polyether ether ketone (PEEK), a liquid crystal polymer, other biocompatible polymer, or other suitable non-conductive material.

[0058] Housing 202 extends between distal end 204 and proximal end 206 along longitudinal axis 210. In some examples, housing can be cylindrical or substantially cylindrical but may be other shapes, e.g., prismatic, or other geometric shapes. Housing 202 may include a delivery tool interface member 208, e.g., at proximal end 206, for engaging with a delivery tool during implantation of device 11. At distal end 204, housing 202 may define a face 205 of housing 202. Face 205 may define a distal end major surface. Face 205 may be orthogonal to longitudinal axis 210. In some examples, face 205 may be slanted, e.g., face 205 may define a reference plane that is not orthogonal to longitudinal axis 210.

[0059] Device 11 includes a ramp 212. Ramp 212 extends from a first end 214A that is fixedly attached to housing 202 at or near distal end 204 (e.g., attached to face 205), to a second end 214B that is more distal to first end 214A. Ramp 212 may be disposed radially outwards of first electrode 132 relative to longitudinal axis 210. Ramp 212 may extend around at least a portion of a perimeter of housing 202. Ramp 212 may extend up to 180 degrees around longitudinal axis 210 and along the perimeter of housing 202. Ramp 212 may be integrally formed as a part of the manufacturing of at least a portion of housing 202 (e.g., as a part of the manufacturing of a header defining distal end 204 and face 205 of housing 202). Ramp 212 may be formed via a molding process, via additive manufacturing, or the like. In some examples ramp 212 is formed separately and affixed to face 205 of housing 202 afterwards. Ramp 212 may define a partial helix, e.g., wound in a same direction and/or in different directions as a helix and/or coil defined by first electrode 132.

[0060] Ramp 212 may define a gradient (i.e., “slope”) from first end 214A to second end 214B. In some examples, ramp 212 may define a linear gradient from first end 214A to second end 214B. For example, ramp 212 may define a steeper slope first end 214A than at second end 214B, or vice versa.

[0061] Ramp 212 may be formed at least partially of an electrically conductive material, such as titanium, platinum, iridium, tantalum, or alloys thereof, and/or of electrically nonconductive material(s). At least portions of ramp 212 may be coated with an electrically insulating coating, e.g., a parylene, polyurethane, silicone, epoxy, or other insulating coating.

[0062] Ramp 212 may be an anti-rotation feature. Ramp 212 may increase compression of the tissue and/or increase the friction or other fixation force between the tissue and device 11 and/or first electrode 132. The increase in fixation force(s) may be sufficient to resist rotation of first electrode 132 by movement of the tissue of heart 16 but may not be sufficient to resist rotation of first electrode 132 by the clinician, e.g., to remove device 11 from heart 16. The amount of force the tissue exerts on first electrode 132 and/or the amount of force ramp 212 exerts on the tissue may vary based on movement of heart 16, movement of device 11, movement of fluid within heart 16, size of heart 16, a number of ramp(s) 212 on face 205, presence of additional anti-rotation feature(s), or the like.

[0063] In some examples, second end 214B of ramp 212 defines a step extending distally from face 205. The step may require the tissue of heart 16 to deform around and/or over ramp 212 to cause device 11 to rotate, thereby increasing an amount of force required to cause device 11 to rotate.

[0064] In some examples, ramp 212 defines a constant width from first end 214A to second end 214B. In some examples, ramp 212 defines a variable width between first end 214A and second end 214B. For example, ramp 212 may define an increasing width from first end 214A to second end 214B. In some examples, a maximum width of ramp 212 is a distance between an outer diameter of housing 202 and an outer diameter of the helix and/or coil defined by first electrode 132. An outer edge (e.g., relative to longitudinal axis 210) of ramp 212 may be coincidental to an outer surface of housing 202. Second end 214B may be separated from face 205 along longitudinal axis by a fixed distance.

[0065] Second end 214B may define a distal surface orthogonal to longitudinal axis 210. Second electrode 134 may be disposed on the distal surface of second end 214B. In some examples, second electrode 134 may be disposed partially along ramp 212, e.g., between first end 214A and second end 214B. Ramp 212 may separate second electrode 134 from face 205 by the fixed distance, e.g., to reduce pacing threshold of second electrode 134 and improve contact between second electrode 134 and wall tissue of the first chamber of heart 16. Ramp 212 may be disposed on face 205 and oriented relative to first electrode 132 to place second electrode 134 and/or second end 214B at particular positions around face 205 relative to first electrode 132. In some examples, second electrode 134 may be disposed on distal face 205 or on a proximal portion of ramp 212 (e.g., at first end 214A).

[0066] Ramp 212 may provide several advantages over another anti-rotation feature (e.g., a deformable spring electrode). Ramp 212 may prevent or inhibit unintended rotation of device 11 without penetrating the tissue of patient 102. Ramp 212 may simplify the manufacturing process and electrical connections with circuitry within housing 202. For example, ramp 212 may be manufactured as a part of a header of housing 202 instead of being assembled separately after the manufacture process. Ramp 212 may also provide increased surface area compared to a deformable spring electrode, thereby increasing an amount of force ramp 212 may resist prior to rotation of device 11.

[0067] First electrode 132 may include one or more coatings (e.g., electrically insulative coating(s)) configured to define a first electrically active region 216, or first electrode 132 may otherwise define first electrically active region 216. In some examples, first electrically active region 216 may be more proximate to the second, e.g., distal, end of first electrode 132. In the example of FIG. 3B, first electrically active region 216 includes the distal end of electrode 132. Second electrode 134 may include one or more coatings configured to define a second electrically active region 217 on an outer surface of electrode 134. In some examples, second electrical active region 217 forms a ring around a therapeutic substance dispensing device 215. Second electrode 134 may include, but is not limited to, may be a button electrode, a spring electrode, or any other suitable type or shape of electrode.

[0068] In the example of FIG. 3B, first electrode 132 takes the form of a helix or a coil. First electrode 132 may be an elongated body defining a helix. In some examples, a helix is an object having a three-dimensional shape like that of a wire wound uniformly in a single layer around a cylindrical or conical surface or mandrel such that the wire would be in a straight line if the surface were unrolled into a plane. First electrode 132 may extend from face 205 from proximal end 220 to a distal end, e.g., defining first electrically active region 216. Proximal end 220 may be a location along first electrode 132 where first electrode 132 extends distally past distal end 204 of device 11.

[0069] Second electrode 134 is disposed on distal end 204 and may include a button electrode, e.g., as illustrated in FIG. 3B, or any other suitable type or shape of electrode. In some examples, device 11 may have a plurality of second electrodes 134 (e.g., two or more second electrodes 134) disposed on distal end 204 of housing 202. The plurality of second electrodes 134 may be equally spaced around a circumference of distal end 204. At least one of the plurality of second electrodes 134 may be disposed on ramps (e.g., on two or more ramps 212). In some examples, each of the plurality of second electrodes 134 may be disposed on ramps. Each ramp 212 may include a single second electrode 134 or two or more second electrodes 134. In some examples, second electrode 134 may be disposed at a predetermined angle away from first end of first electrode 132.

[0070] In some examples, first electrode 132 may include one or more additional antirotation features. The additional anti-rotation features may include a shape of first electrode 132, dimensions (e.g., outer diameter, pitch, or the like) of first electrode 132, one or more features disposed on an outer surface of first electrode 132, or the like. The shape and/or dimensions of first electrode 132 may include a geometric shape of first electrode 132, a varying diameter configuration of first electrode 132, a varying pitch configuration of first electrode 132, a waveform configuration of first electrode 132, or any combination herein. The one or more anti-rotation features disposed on first electrode 132 may include, but are not limited to, elongate darts, barbs, or tines. In some examples, the anti-rotation features include bumps, ridges, and/or other texturing disposed on one or more surfaces of ramp 212 and/or of face 205. The one or more anti-rotation features may resist rotation of first electrode 132 (e.g., by penetrating the tissue, by increasing the friction between first electrode 132 and the tissue, or the like) alone or in conjunction with other anti-rotation features (e.g., ramp 212).

[0071] As illustrated in FIG. 3B, first electrode 132 may be a helix extending distally from face 205 and revolving around longitudinal axis 210 in a counter-clockwise direction (i.e., “wound” in a counter-clockwise direction, and ramp 212 may define partial helix extending distally from face 205 and revolving around longitudinal axis 210 in a clockwise direction, although in other examples the first electrode 132 and ramp 212 may revolve around longitudinal axis 210 in different directions (e.g., first electrode 132 revolves around longitudinal axis 210 in a clockwise direction and ramp 212 revolves around longitudinal axis 210 in a counter-clockwise direction) or first electrode 132 and ramp 212 may revolve around longitudinal axis 210 in a same direction. Designing ramp 212 to revolve around longitudinal axis 210 in the same direction as first electrode 132 may increase the resistance to insertion and reduce the resistance to removal of device 11 by the clinician while increasing the resistance to rotation of device 11 by movement of the tissue and/or movement of heart 16. In some examples, first electrode 132 and ramp 212 may revolve around longitudinal axis 210 in different directions. In such examples, designing first electrode 132 and ramp 212 to revolve around longitudinal axis 210 in different directions may reduce the resistance to insertion and increase the resistance to removal of device 11 by the clinician. In the example of FIG. 3B, the helix and partial helix defined by first electrode 132 and ramp 212, respectively, have the same pitch, although they may have different pitches in other examples. In some examples, first electrode 132 defines a varying pitch along longitudinal axis 210. In some examples, one or both of first electrode 132 and ramp 212 may define a shape other than helical. For example, first electrode 132 may define a geometrical shape (e.g., a triangular shape, a rectangular shape, a hexagonal shape, an octagonal shape, a lobed shape, or the like). Such a geometrical shape may be equilateral. The geometrical shape may function as an antirotation feature.

[0072] In some examples, ramp 212 may cause second electrode 134 to maintain consistent contact with the wall tissue, e.g., by raising second electrode 134 from face 205 by a fixed distance. Consistent contact between second electrode 134 and the wall tissue may improve electrical conductivity and the delivery of electrical signals from second electrode 134 to the wall tissue. In some examples, where device 11 is an implantable pacing device, the consistent contact between second electrode 134 and the wall tissue may reduce and/or maintain a pacing threshold for a chamber (e.g., the right atrium) of heart 16.

[0073] It should be understood that, notwithstanding the specific examples of IMDs and pacing devices disclosed herein, such as pacing device 10, pacing device 11, and pacing device 12, the techniques disclosed herein for, inter alia, detection of HF may be implemented in any suitable IMD or pacing device.

[0074] FIG. 4A is a conceptual block diagram of an example IMD 400, in accordance with one or more aspects of this disclosure. In some examples, IMD 400 may represent an example of pacing device 12, as shown in FIG. 2, pacing device 10, as shown in FIG. 3A, or pacing device 11, as shown in FIG. 3B. FIGS. 2-4A show an examples of IMD 400 and/or pacing device 12 having two or three electrodes. However, the number of electrodes illustrated in FIGS. 2-4 are examples, and other numbers of electrodes may be included in IMD 400, pacing device 12, or pacing device 10, such as, but not limited to, 2- 10 electrodes. In some examples, the number of electrodes included in IMD 400, pacing device 12, pacing device 11, or pacing device 10 may be more than 10 electrodes.

[0075] In the illustrated example, IMD 400 may include one or more of processing circuitry 490, memory 492, therapy generation circuitry 496, sensing circuitry 498, a motion sensor 480, and/or communication circuitry 494. One or more of the elements of IMD 400 may be part of an electronics module. For example, processing circuitry 490, memory 492, therapy generation circuitry 496, sensing circuitry 498, motion sensor 480, and/or communication circuitry 494 may be mounted on a circuit board of an electronics module of IMD 400.

[0076] Memory 492 may include computer-readable instructions that, when executed by processing circuitry 490, cause IMD 400 and processing circuitry 490 to perform various functions of IMD 400 such as storing and analyzing signals received by IMD 400 and providing pacing therapy for a patient’s heart.

[0077] Memory 492 may include 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 any other digital or analog media.

[0078] Processing circuitry 490 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, processing circuitry 490 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 processing circuitry 490 herein may be embodied as software, firmware, hardware or any combination thereof.

[0079] Processing circuitry 490 may control therapy generation circuitry 496 to deliver stimulation therapy to heart 16 of patient 14 according to therapy parameters, which may be stored in memory 492. For example, processing circuitry 490 may control therapy generation circuitry 496 to deliver electrical pulses with the amplitudes, pulse widths, frequency, or electrode polarities specified by the therapy parameters. In this manner, therapy generation circuitry 496 may deliver pacing pulses to the heart via electrodes 452, 456, and/or 460. Although IMD 400 may only include two electrodes, e.g., electrodes 452 and 460, IMD 400 may utilize three or more electrodes in other examples. IMD 400 may use any combination of electrodes to deliver therapy and/or detect electrical signals from the patient. [0080] Therapy generation circuitry 496 may be electrically coupled to electrodes 452, 456, and/or 460 positioned on the housing of IMD 400. In the illustrated example, therapy generation circuitry 496 is configured to generate and deliver electrical stimulation therapy to the heart. For example, therapy generation circuitry 496 may deliver pulses to a portion of cardiac muscle within the heart via electrodes 452, 456, and/or 460. In some examples, therapy generation circuitry 496 may deliver pacing stimulation in the form of electrical pulses. Therapy generation circuitry 496 may include charging circuitry, and one or more charge storage devices, such as one or more capacitors. Switching circuitry (not shown) may control when the capacitor(s) are discharged to electrodes 452 and 460.

[0081] Sensing circuitry 498 may monitor signals from at least one of electrodes 452, 456, and 460 to monitor electrical activity of the heart, impedance, or another electrical phenomenon. Sensing may be done to determine heart rates or heart rate variability, to detect ventricular dyssynchrony, arrhythmias (e.g., tachyarrhythmias), to detect cardiac depolarizations for determining whether an intrinsic depolarization occurs prior to expiration of an escape interval for delivering cardiac pacing, or other electrical signals. Sensing may be done to determine a workload of a heart. Sensing circuitry 498 may include switching circuitry to select the electrode polarity used to sense the heart activity. In examples with more than two electrodes, processing circuitry 490 may select the electrodes that function as sense electrodes, i.e., select the sensing configuration, via the switching circuitry within sensing circuitry 498. In some examples, electrode 452 is connected to a first pole of a battery of IMD 400 (e.g., the positive terminal of the battery), electrode 460 is connected to a second pole of the battery (e.g., the case ground), and electrode 456 is a sense electrode configured to receive signals in the environment surrounding IMD 400. Other configurations of electrodes 452, 456, and 460 are also possible.

[0082] Motion sensor 480 may be contained within the housing of IMD 400 and include one or more accelerometers, gyroscopes, electrical or magnetic field sensors, or other devices capable of detecting motion and/or position of IMD 400. For example, motion sensor 480 may include a three-axis accelerometer (three-dimensional accelerometer) that is configured to detect an accelerometer signal, such as accelerations in any direction in space. Specifically, the three-axis accelerometer may be used to detect the motion of IMD 400 that may be indicative of cardiac events, noise, and/or cardiac workload. In some examples, motion sensor 480 may include a 6-axis accelerometer configured to detect an accelerometer signal. In some examples, motion sensor 480 may include a 9-axis accelerometer configured to detect an accelerometer signal. The motion sensor(s) 480 may be sensitive to the motion of the heart 16, including the paced activation of the ventricles. The motion sensor(s) 480 may also be sensitive to the gross body motion, e.g., activity level, or patient 14.

[0083] While processing circuitry 490 controls therapy generation circuitry 496 to deliver ventricular pacing pulses, processing circuitry 490 may also control or monitor motion sensor(s) 480 to generate a signal that varies with the cardiac contraction. In some examples, motion sensor(s) 480 may generate the signal substantially continuously. Processing circuitry 490 may identify one or more features of the cardiac contraction within the signal, on a beat-by-beat basis, or otherwise, to facilitate, e.g., delivery of ventricular pacing pulses in an atrial- synchronized manner. In some examples, a cardiac pacing rate function is a function that allows processing circuitry of a cardiac pacemaker or other device of a system including a pacemaker, to determine a rate for cardiac pacing to be delivered to a patient, (e.g., an escape interval value for cardiac pacing). A cardiac pacing rate function may include a combination of linear and/or non-linear functions (e.g., multiple linear functions having different slopes) with set points between the functions. In some examples, a cardiac pacing rate function may be stored in memory 492 and used by processing circuitry 490 to select a cardiac pacing rate from the cardiac pacing rate function based on patient activity level determined from the motion sensor(s) 480 and/or based on another sensed physiological signal indicative of exertion of patient, such as respiration. Processing circuitry 490 may control therapy generation circuitry 496 to deliver cardiac pacing based on the selected cardiac pacing rate.

[0084] Although described as primarily being performed by processing circuitry 490 of IMD 400, the techniques described throughout may be performed, in whole or in part, by processing circuitry and memory of other devices of a medical device system, such as external device 24, server 112, or computing device 114, as described herein.

[0085] In some examples, processing circuitry 490 may be configured to determine one or more cardiac activity counts of a heart 16 of patient 14 based on a motion signal generated by motion sensor 480 of IMD 400 based on motion of patient 14 and heart 16. For example, as shown in FIG. 4B, processing circuitry 490 may apply a filter 412 to an accelerometer signal 410. In some examples, filter 412 is a 1 Hertz (Hz) to 10 Hz bandpass filter. In some examples, filter 412 is a 10 Hz to 30 Hz bandpass filter. In some examples, filter 412 may include a low-pass filter 412A and a high-pass filter 412B. In some examples, processing circuitry 490 may rectify 414 the filtered accelerometer signal. [0086] In some examples, processing circuitry 490 may apply a discrete integration 416 to the rectified filtered accelerometer signal to determine one more cardiac activity counts 418. For example, processing circuitry 490 may apply the discrete integration for a period of time, such as between 1.5 seconds to 2.5 seconds, to determine a particular cardiac activity count corresponding to the particular period of time. In some examples, a particular cardiac activity count of the one more cardiac activity counts corresponds to an amount of energy used by the heart 16 of patient 14 during the period of time the particular cardiac activity count is determined, i.e., the period of time of the rectified filtered signal which is integrated.

[0087] In some examples, processing circuitry 490 may determine cardiac activity counts during periods of time where patient is at rest. For example, cardiac activity counts 418 may be referred to as resting cardiac activity counts. For example, processing circuitry 490 may use a particular percentile of activity data (e.g., accelerometer signal), such as a particular percentile less than 80^th percentile, to determine cardiac activity counts 418. In some examples, processing circuitry 490 may use a median activity data (e.g., accelerometer signal) when IMD 400 is pacing at a lower rate, such as when IMD 400 is pacing at a resting rate, to determine cardiac activity counts 418. In some examples, other percentiles or averages of activity data (e.g., accelerometer signal), either in total or during lower pacing rates, may be used to determine cardiac activity counts 418. In some examples, processing circuitry 490 may determine an indication of heart failure based on the one or more cardiac activity counts 418, and output information pertaining to the determined indication of heart failure to a device or network.

[0088] In some examples, processing circuitry 490 may be configured to determine a value of a first resting cardiac activity count during a first period of time based on the one or more cardiac activity counts determined during the first period of time and determine a value of a second resting cardiac activity count during a second period of time based on the one or more cardiac activity counts determined during the second period of time, the second period of time being after the first period of time, and determine the indication of heart failure based on the first resting cardiac activity count and the second resting cardiac activity count. For example, processing circuitry 490 may determine the indication of heart failure based on a difference between the value of the first resting cardiac activity count and the value of the second resting cardiac activity count. In some examples, processing circuitry 490 may determine heart failure is worsening due to a value of cardiac activity counts decreasing over a period of time, such as days, weeks, months, or years. For example, processing circuitry 490 may determine an amount of energy used by a heart during a period of time is decreasing based, at least in part, on a value of cardiac activity counts decreasing over the period of time. Processing circuitry 490 may then determiner heart failure is worsening based, at least in part, on the amount of energy used by a heart decreasing during the period of time.

[0089] In some examples, processing circuitry 490 may be configured to determine a workload of heart 16 using a motion signal sensed via one or more motion sensor(s) 480 and/or the electrical activity sensed via at least one of electrodes 452, 456, and 460. In some examples, as shown in FIG. 4C, the y-axis may be indicative of the paced heart rate. The x-axis may be indicative of the workload of a heart 16 of patient 14. In some examples, a value of cardiac activity count 418 may be indicative of a workload of heart 16. In some examples, the paced heart rate (y-axis) is based on the workload of the heart 16. For example, when a value of workload of a heart is lower (e.g., moving to the left of the x-axis in FIG. 4C) the paced heart rate decreases.

[0090] In some examples, a setpoint, such as 402 or 404, may correspond and/or indicate a value of workload of heart 16, and a pacing rate 406 may be based, at least in part, on a setpoint. It should be noted that in FIG. 4C the setpoints 402, 404 illustrate operating states at two different points in time, or under two different conditions; in practice, only one of the setpoints 402, 404 is used to influence the therapy generation circuitry 496. In some examples, pacing rate 406 may be a predetermined pacing rate, and the setpoint 402, 404 may be a predetermined workload. For example, a setpoint 402, 404 may correspond to a pacing rate 406. For example, in FIG. 4C, a pacing rate 406 and setpoint 402, 404 is set, e.g., by clinician programming, at 95 beats per minute when experiencing a workload of 20 cardiac activity counts 418. However, pacing rate 406 may be other values indicative of heart beats per a period of time, and the setpoint 402, 404 may be other values indicative of a given level of activity. In some examples, one or more of the first setpoint and/or the second setpoint may be an activity of daily living (ADL) setpoint. In some examples, pacing rate 406 may be an ADL pacing rate 406.

[0091] In some examples, the processing circuitry 490 may adjust the setpoint 402, 404 since they do not adequately reflect the behavior of patient 14. For example, in FIG. 4D, processing circuitry 490 may be programmed, such as by a clinician, to have a target rate histogram 430. In some examples, a target histogram 430 may be set indirectly via a list of qualitative settings, such as setting an “ADL Response Value” to a scale from “Inactive” to “Very Active.” Then, over a period of time, such as one day or one week, the sensing circuitry 498 may sense and/or collect data on the patient’s heart rate and store it in memory 492. At a regular interval, such as every day or every week, the processing circuitry 490 may form a rate profile 420 based on the sensed data. Processing circuitry 490 may compare the rate profile 420 to the target histogram 430 to determine whether the motion sensors 480 and processing circuitry 490 are detecting patient activity levels appropriately, and a new setpoint 404 may be established to account for this. In FIG. 4D, the x-axis for the rate profile 420 and the target histogram 430 correspond to levels of heart rates that increase from left to right. In FIG. 4D, the y-axis corresponds to incidence of those heart rates, such as an amount of time over period of time, such as day(s) or week(s), a heart rate is at particular levels, and the y-axis increases from bottom to top. [0092] For example, a patient 14 may have a rate profile 420 that reflects significant time at lower heart rates compared to the target histogram 430 while an ADL setpoint is configured to the first setpoint 402. In some examples, a rate profile 420 may reflect significant time at lower heart rates because the IMD 400 may have a lower range of motion in the heart 16, so the cardiac activity counts 418 are lower than the nominal setting while the patient is active. In response, the processing circuitry 490 may change an ADL setpoint to a lower second setpoint 404 which would be used to dictate the pacing rates for patient 14. When this occurs, the second setpoint 404 may replace the first setpoint 402 to inform the therapy generation circuitry 496. In some examples, previously recorded setpoints 402 may be stored in memory 492. In some examples, processing circuitry 490 may replace the first setpoint 402 with the second setpoint 404 to decrease a threshold to pace at the ADL rate to account for a lower range of motion in the heart 16. After a period of time, such as a week, processing circuitry 490 may determine whether a new rate profile more closely matches the target histogram 430. [0093] In some examples, a workload of a heart may decrease for a variety of reasons, such as patient 16 being ill, having HF, and/or being less active. In some examples, as workload of heart 16 decreases, processing circuitry 490 may shift a setpoint lower, such as shifting a setpoint from the first setpoint 402 to the second setpoint 404, to provide, by the IMD 400, the pacing rate 406 at a lower workload of the heart to help a patient’ s heart achieve a targeted amount of active heart rate when the heart has a lower workload. In some examples, by shifting a setpoint to a lower value, such as second setpoint 404, the heart 16 may be paced at higher rates with a respective heart workload than the heart would have been paced with the first setpoint 402, as a slope with respect to the second setpoint 404 may be steeper than a slope with respect to the first setpoint 402. In some examples, increasing pacing that results in a steeper slope may help support oxygen demand even though the heart may be failing and have weaker contractions.

[0094] In some examples, processing circuitry 490 may determine a first setpoint 402 based on a workload of the heart 16 during a first period of time, such as days, weeks, or months following implant, and determine a second setpoint based on a workload of the heart during a second period of time, the second period of time being after the first period of time. In some examples, a setpoint, such as 402 or 404, may correspond to a value of a cardiac activity count 418 that corresponds to a workload of the heart. In some examples, processing circuitry 490 may determine a value of cardiac motion of the heart based, at least in part, on the first setpoint 402 and/or the second setpoint 404. For example, processing circuitry 490 may determine a change between the first setpoint 402 and the second setpoint 404 and determine the value of cardiac motion of the patient based, at least in part, on the change between the first setpoint 402 and the second setpoint 404. In some examples, the change in setpoints and/or setpoint trends may be a surrogate for measuring cardiac motion. For example, a second setpoint 404 being less than a first setpoint 402 may indicate a decrease of intrinsic cardiac motion of the heart. A second setpoint 404 being greater than a first setpoint 402 may indicate an increase of intrinsic cardiac motion. In some examples, the change in setpoints and/or setpoint trends may be extended beyond two setpoints 402, 404 by leveraging memory 492 to track historic setpoint 402, 404 data. For example, even though a second setpoint 404 may be more than the first setpoint 402, correlating an additional six setpoints stored in memory 492 may reveal a longer-term negative trend, which may indicate a decrease of intrinsic cardiac motion. Processing circuitry 490 may determine an indication of heart failure based on the determined value of cardiac motion and determine whether the indication of HF satisfies a HF threshold. For example, a decrease of cardiac motion of a particular period of time satisfying a HF threshold may indicate HF and/or worsening HF. In some examples, processing circuitry 490 may generate a remediation action in response to determining the indication of HF satisfies a HF threshold.

[0095] FIG. 5 is a block diagram illustrating an example configuration of components of external device 24. In the example of FIG. 5, external device 24 includes processing circuitry 80, communication circuitry 82, storage device 84, and user interface 86.

[0096] Processing circuitry 80 may include one or more processors that are configured to implement functionality and/or process instructions for execution within external device 24. For example, processing circuitry 80 may be capable of processing instructions stored in storage device 84. Processing circuitry 80 may include, for example, microprocessors, DSPs, ASICs, FPGAs, or equivalent discrete or integrated logic circuitry, or a combination of any of the foregoing devices or circuitry. Accordingly, processing circuitry 80 may include any suitable structure, whether in hardware, software, firmware, or any combination thereof, to perform the functions ascribed herein to processing circuitry 80. [0097] Communication circuitry 82 may include any suitable hardware, firmware, software or any combination thereof for communicating with another device, such as IMD 400. Under the control of processing circuitry 80, communication circuitry 82 may receive downlink telemetry from, as well as send uplink telemetry to, IMD 400, or another device. Communication circuitry 82 may be configured to transmit or receive signals via inductive coupling, electromagnetic coupling, Near Field Communication (NFC), Radio Frequency (RF) communication, Bluetooth, WiFi, or other proprietary or non-proprietary wireless communication schemes. Communication circuitry 82 may also be configured to communicate with devices other than IMD 400 via any of a variety of forms of wired and/or wireless communication and/or network protocols.

[0098] Storage device 84 may be configured to store information within external device 24 during operation. Storage device 84 may include a computer-readable storage medium or computer-readable storage device. In some examples, storage device 84 includes one or more of a short-term memory or a long-term memory. Storage device 84 may include, for example, RAM, DRAM, SRAM, magnetic discs, optical discs, flash memories, or forms of EPROM or EEPROM. In some examples, storage device 84 is used to store data indicative of instructions for execution by processing circuitry 80. Storage device 84 may be used by software or applications running on external device 24 to temporarily store information during program execution.

[0099] Data exchanged between external device 24 and IMD 400 may include operational parameters. External device 24 may transmit data including computer readable instructions which, when implemented by IMD 400, may control IMD 400 to change one or more operational parameters and/or export collected data. For example, processing circuitry 80 may transmit an instruction to IMD 400 which requests IMD 400 to export collected data (e.g., HF data, heart sound features, digitized cardiac EGM signals, digitized cardiac counts, and/or digitized accelerometer signals) to external device 24. In turn, external device 24 may receive the collected data from IMD 400 and store the collected data in storage device 84. Processing circuitry 80 may implement any of the techniques described herein to analyze heart sound features, cardiac electrogram signals, and/or heart sound beat signals received from IMD 400, e.g., to determine an indication of HF.

[0100] A user, such as a clinician or patient 14, may interact with external device 24 through user interface 86. User interface 86 includes a display (not shown), such as a liquid crystal display (LCD) or a light emitting diode (LED) display or other type of screen, with which processing circuitry 80 may present information related to IMD 400, e.g., electrical activity of a heart, cardiac EGMs, accelerometer signals, heart sound signals, values of heart workload, values of cardiac motion, values of one or more cardiac activity counts, indications of detections or predictions of HF, and quantifications of HF, such as a quantification of change in HF over a period of time (e.g., improving or worsening) or likelihood of an HF event. In addition, user interface 86 may include an input mechanism to receive input from the user. The input mechanisms may include, for example, any one or more of buttons, a keypad (e.g., an alphanumeric keypad), a peripheral pointing device, a touch screen, or another input mechanism that allows the user to navigate through user interfaces presented by processing circuitry 80 of external device 24 and provide input. In other examples, user interface 86 also includes audio circuitry for providing audible notifications, instructions or other sounds to the user, receiving voice commands from the user, or both. [0101] FIG. 6 is a block diagram illustrating a system 115 that includes an external device 112, such as a server, and one or more computing devices 114A-114N that are coupled to IMD 400 and external device 24 shown in FIG. 1 via a network 120, according to one example. In this example, IMD 400 uses communication circuitry 494 (FIG. 4A) to communicate with external device 24 via a first wireless connection, and to communicate with an access point 122 via a second wireless connection. In the example of FIG. 5, access point 122, external device 24, external device 112, and computing devices 114A- 114N are interconnected, and able to communicate with each other, through network 120. In some cases, one or more of access point 122, external device 24, external device 112, and computing devices 114A-114N may be coupled to network 120 through one or more wireless connections. IMD 400, external device 24, external device 112, and computing devices 114A-114N may each comprise one or more processing circuitries, such as one or more microprocessors, DSPs, ASICs, FPGAs, programmable logic circuitry, or the like, that may perform various functions and operations, such as those described herein.

[0102] Access point 122 may comprise a device that connects to network 120 via any of a variety of connections, such as telephone dial-up, digital subscriber line (DSL), or cable modem connections. In other examples, access point 122 may be coupled to network 120 through different forms of connections, including wired or wireless connections. In some examples, access point 122 may communicate with external device 24 and/or IMD 400. Access point 122 may be co-located with patient 14 (e.g., within the same room or within the same site as patient 14) or may be remotely located from patient 14. For example, access point 122 may be a home monitor that is located in the patient’s home or is portable for carrying with patient 14.

[0103] During operation, IMD 400 may collect, measure, and store various forms of diagnostic data. For example, as described previously, IMD 400 may sense accelerometer signals, determine one or more cardiac activity counts of a heart 16 of the patient 14 based on the accelerometer signal, determine an indication of heart failure based on the one or more cardiac activity counts, and output information pertaining to the determined indication of heart failure to a device or network. For example, as described previously, IMD 400 may sense electrical activity of a heart 16 of patient 14, determine a workload of a heart based, at least in part, on the sensed electrical activity, determine a first setpoint based on a workload of a heart during a first period of time, determine a second setpoint based on a workload of a heart during a second period of time, the second period of time being after the first period of time, determine a value of cardiac motion of the patient based, at least in part, on the first setpoint and the second setpoint, and determine an indication of heart failure based on the determined value of cardiac motion.

[0104] In certain cases, IMD 400 may directly analyze sensed diagnostic data and generate any corresponding reports or alerts. In some cases, however, IMD 400 may send diagnostic data to external device 24, access point 122, and/or external device 112, either wirelessly or via access point 122 and network 120, for remote processing and analysis. [0105] In one example, external device 112 may comprise a secure storage site for information that has been collected from IMD 400 and/or external device 24. In this example, network 120 may comprise an Internet network; and trained professionals, such as clinicians, may use computing devices 114A-114N to securely access stored data on external device 112. For example, the trained professionals may need to enter usernames and passwords to access the stored information on external device 112. In one embodiment, external device 112 may be a CareLink server provided by Medtronic, Inc., of Minneapolis, Minnesota.

[0106] In some examples, processing circuitry and memory of one or more of access point 122, server 112, or computing devices 114, e.g., processing circuitry 118, input/output device 116, and memory of server 112, may be configured to provide some or all of the functionality ascribed to processing circuitry 490 and memory 492 of IMD 400. In some examples, processing circuitry 118 may be configured to determine one or more cardiac activity counts of a heart 16 of the patient 14 based on the accelerometer signal, determine an indication of heart failure based on the one or more cardiac activity counts, and output information pertaining to the determined indication of heart failure to a device or network. In some examples, processing circuitry 118 may be configured to determine a workload of a heart of the patient based, at least in part, on the sensed electrical activity, determine a first setpoint based on a workload of a heart during a first period of time, determine a second setpoint based on a workload of a heart during a second period of time, the second period of time being after the first period of time, determine a value of cardiac motion of the patient based, at least in part, on the first ADL setpoint and the second ADL setpoint, and determine an indication of heart failure based on the determined value of cardiac motion. [0107] FIGS. 7-8 are flow diagrams illustrating various techniques related to determining an indication of heart failure, in accordance with examples of this disclosure. As described herein, the techniques illustrated FIGS. 7-8 may be employed using one or more components of system 115, which have been described above with respect to FIGS. 1-6. Although described as being performed by processing circuitry 490 of IMD 400, the techniques of FIGS. 7-8 may be performed, in whole or in part, by processing circuitry and memory of other devices of a medical device system, as described herein.

[0108] In the example of FIG. 7, processing circuitry 490 may determine one or more cardiac activity counts of a heart 16 of based on an accelerometer signal (700). In some examples, IMD 400 may include an accelerometer configured to detect an accelerometer signal over a period of time. In some examples, a particular cardiac activity count of the one more cardiac activity counts may corresponds to an amount of energy used by the heart 16 during a period of time the particular cardiac activity count is determined. In some examples, the cardiac activity counts during periods of time where patient is at rest to compare different values of resting cardiac activity counts. Processing circuitry 490 may determine an indication of HF based on the one or more cardiac activity counts (702). Processing circuitry 490 may output information pertaining to the determined indication of HF to a device or network (704). In some examples, processing circuitry 490 may determine the indication of HF satisfies a HF threshold (706). In some examples, processing circuitry 490 may generate a remediation action in response to the determination that the indication of HF satisfies a HF threshold (708). In some examples, the remediation action may include modifying a therapy, such as modifying a pacing therapy.

[0109] In the example of FIG. 8, processing circuitry 490 may determine a rate profile 420 of a heart 16 based on heart rate data stored in memory 492 over a period of time, such as a day or a week (800). In some examples, IMD 400 may include a sensor, such as at least one of a plurality of electrodes 452, 456, 460, and/or at least one motion sensor 480, configured to detect the heart rate. Processing circuitry 490 may compare the rate profile to a target histogram 430 (802). Processing circuitry 490 may determine whether a change in a setpoint 402 may adjust a rate profile of a patient to match the target histogram 430 (804). For example, processing circuitry 490 may determine an initial activity setpoint 402 by adjusting it until the rate histogram 420 sufficiently matches the target histogram 430 set by a clinician based on anticipated patient activity levels. This process 802 of getting an initial activity setpoint may take a period of time after implant, such as one to three months, as a new rate histogram must be collected at each incremental adjustment of the setpoint, and it could take multiple iterations to adapt to a “steady state” due to a patient’s individual situation. Factors that may influence this initial setpoint so that it deviates from nominal clinician-set values could include individual physiology, recovery from surgery, and encapsulation or healing around IMD 400.

[0110] Processing circuitry 490 may determine a second setpoint 404 based on the rate histogram 420 of the heart during a subsequent time period (804). In some examples, a second period of time may take place after the processing circuitry 490 has determined an initial activity setpoint 402 based on patient physiology and the patient has been given sufficient time to recover from surgery. In some examples, a setpoint, such as 402 or 404, may correspond and/or indicate a value of workload of heart 16, and a pacing rate 406 may be based, at least in part, on a setpoint. In some examples, one or more of the first setpoint and/or the second setpoint may be an ADL setpoint. In some examples, pacing rate 406 may be an ADL pacing rate.

[0111] Processing circuitry 490 may determine a trend in patient activity or cardiac motion which may, in part, correlate with the relationship between the first setpoint 402 and the second setpoint 404 (806). For example, processing circuitry 490 may determine a change between the first setpoint 402 and the second setpoint 404 and determine the value of cardiac motion of the patient based, at least in part, on the change between the first setpoint 402 and the second setpoint 404. In some examples, the change in setpoints and/or setpoint trends may be a surrogate for measuring cardiac motion. For example, a second setpoint 404 being less than a first setpoint 402 may indicate a decrease of intrinsic cardiac motion of the heart. A second setpoint 404 being greater than a first setpoint 402 may indicate an increase of intrinsic cardiac motion.

[0112] In some examples, processing circuitry 490 may determine determination of these trends 806 may be performed over a longer period of time by storing more than two setpoints. In some examples, this trend may also rely on more than two subsequent setpoints by storing up to a predetermined amount of most recent setpoints, such as up to the most recent 26 setpoints over the course of six months. In some examples, a “buffer” of setpoints may be uploaded to an external server 112 on a regular basis, such as during clinician check-ins, to allow tracking of a patient’s long-term history while conserving the comparatively limited space in the memory 492 of an IMD 400. These extended datasets may be used in a similar manner to indicate a potential decrease of intrinsic cardiac motion of the heart.

[0113] Processing circuitry 490 may determine an indication of heart failure based on the determined trend in cardiac motion or activity (808). For example, a decrease of cardiac motion of a particular period of time satisfying a HF threshold may indicate HF and/or worsening HF. Processing circuitry 490 may output information pertaining to the determined indication of HF to a device or network (810). In some examples, processing circuitry 490 may determine the indication of HF satisfies a HF threshold (812). In some examples, processing circuitry 490 may generate a remediation action in response to the determination that the indication of HF satisfies a HF threshold (814). In some examples, the remediation action may include modifying a therapy, such as modifying a pacing therapy.

[0114] In the example of FIG. 9, processing circuitry 490 may determine a parameter indicative of workload of a heart 16 based on a detected signal indicative of a workload of the heart (900). In some examples, a parameter indicative of workload of a heart 16 may be rate profile 420 of a heart 16 based on rate data. In some examples, IMD 400 may include a sensor, such as at least one of a plurality of electrodes 452, 456, 460, and/or at least one motion sensor 480, configured to detect a signal indicative of a workload of a heart. Processing circuitry 490 may determine a first setpoint 402 based on a workload of the heart during a first time period (902). Processing circuitry 490 may determine a second setpoint 402 based on a workload of the heart during a second time period (904). The second period of time being after the first period of time. In some examples, a setpoint, such as 402 or 404, may correspond and/or indicate a value of workload of heart 16, and a pacing rate 406 may be based, at least in part, on a setpoint. In some examples, one or more of the first setpoint and/or the second setpoint may be an ADL setpoint. In some examples, pacing rate 406 may be an ADL pacing rate.

[0115] Processing circuitry 490 may determine a value of cardiac motion of the patient 14 based, at least in part, on the first setpoint 402 and the second setpoint 404 (906). For example, processing circuitry 490 may determine a change between the first setpoint 402 and the second setpoint 404 and determine the value of cardiac motion of the patient based, at least in part, on the change between the first setpoint 402 and the second setpoint 404. For example, processing circuitry 490 may determine a difference between the first setpoint 402 and the second setpoint 404 and determine the value of cardiac motion of the patient based, at least in part, on the difference between the first setpoint 402 and the second setpoint 404. In some examples, the change in setpoints and/or setpoint trends may be a surrogate for measuring cardiac motion. For example, a second setpoint 404 being less than a first setpoint 402 may indicate a decrease of intrinsic cardiac motion of the heart. A second setpoint 404 being greater than a first setpoint 402 may indicate an increase of intrinsic cardiac motion.

[0116] Processing circuitry 490 may determine an indication of heart failure based on the determined value of cardiac motion (908). For example, a decrease of cardiac motion of a particular period of time satisfying a HF threshold may indicate HF and/or worsening HF. Processing circuitry 490 may output information pertaining to the determined indication of HF to a device or network (910). In some examples, processing circuitry 490 may determine the indication of HF satisfies a HF threshold (912). In some examples, processing circuitry 490 may generate a remediation action in response to the determination that the indication of HF satisfies a HF threshold (914). In some examples, the remediation action may include modifying a therapy, such as modifying a pacing therapy.

[0117] It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). In addition, while certain aspects of this disclosure are described as being performed by a single module, unit, or circuit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units, modules, or circuitry associated with, for example, a medical device.

[0118] In one or more examples, the described techniques 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 non-transitory computer-readable 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).

[0119] 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 (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” or “processing circuitry” as used herein may refer to any of the foregoing structure or any other physical structure suitable for implementation of the described techniques. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0120] Furthermore, although described primarily with reference to examples that provide an information pertaining to a determined indication of heart failure in response to determining an indication of heart failure based on the one or more cardiac activity counts, other examples may additionally or alternatively automatically modify a therapy in response to determining an indication of heart failure based on the one or more cardiac activity counts in the patient. The therapy may be, as examples, a substance delivered by an implantable pump, cardiac resynchronization therapy, refractory period stimulation, or cardiac potentiation therapy. These and other examples are within the scope of the following claims.

[0121] The following examples are illustrative of the techniques described herein.

[0122] Example 1: A system includes an implantable medical device (IMD) configured to be implanted in a patient, the IMD comprising a motion sensor configured to generate a motion signal based on cardiac motion over a period of time; and processing circuitry configured to: determine one or more cardiac activity counts of a heart of the patient based on the motion signal; determine an indication of heart failure based on the one or more cardiac activity counts; and output information pertaining to the indication of heart failure to a device or network.

[0123] Example 2: The system of example 1, wherein to determine cardiac activity counts based on the motion signal, the processing circuitry is further configured to: apply a filter to the motion signal; rectify the filtered motion signal; and apply a discrete integration to the rectified filtered motion signal to determine a particular cardiac activity count of the one more cardiac activity counts.

[0124] Example 3: The system of example 2, wherein the filter is a 1 Hertz (Hz) to 10 Hz bandpass filter.

[0125] Example 4: The system of example 2, wherein the filter is a 10 Hertz (Hz) to 30 Hz bandpass filter.

[0126] Example 5: The system of any of examples 2-4, wherein processing circuitry is further configured to apply the discrete integration for a period of time between 1.5 seconds to 2.5 seconds.

[0127] Example 6: The system of any of examples 1-5, wherein the processing circuitry is further configured to: determine a value of a first resting cardiac activity count during a first period of time based on the one or more cardiac activity counts determined during the first period of time; determine a value of a second resting cardiac activity count during a second period of time based on the one or more cardiac activity counts determined during the second period of time, the second period of time being after the first period of time; and determine the indication of heart failure based on the first resting cardiac activity count and the second resting cardiac activity count.

[0128] Example 7: The system of example 6, wherein the processing circuitry is further configured to determine the indication of heart failure based on a difference between the value of the first resting cardiac activity count and the value of the second resting cardiac activity count.

[0129] Example 8: The system of any of examples 1-7, wherein a particular cardiac activity count of the one more cardiac activity counts corresponds to energy used by the heart during a period of time the particular cardiac activity count is determined.

[0130] Example 9: The system of any of examples 1-8, wherein the processing circuitry is further configured to determine the indication of heart failure satisfies a heart failure threshold; and generate a remediation action in response to the determination that the indication of heart failure satisfies the heart failure threshold.

[0131] Example 10: The system of example 9, wherein the remediation action includes modifying a therapy.

[0132] Example 11: The system of any of examples 1-10, wherein the motion sensor comprises at least an accelerometer. [0133] Example 12: A system includes an implantable medical device includes a sensor configured to detect a signal indicative of a workload of a heart of a patient; and therapy generation circuitry configured to deliver cardiac pacing to the heart; and processing circuitry configured to: determine a value of a parameter indicative of workload of the heart of the patient based on the detected signal; control the therapy generation circuitry to deliver the cardiac pacing at a pacing rate based on the value of the parameter and a predetermined relationship between values of the parameter and cardiac pacing rates; determine a first setpoint for the predetermined relationship based on a value of a parameter indicative of a workload of the heart during a first period of time; determine a second setpoint for the relationship based on a value of a parameter indicative of a workload of the heart during a second period of time, the second period of time being after the first period of time; determine an indication of heart failure based, at least in part, on the first setpoint and the second setpoint; and output information pertaining to the indication of heart failure to a device or network.

[0134] Example 13: The system of example 12, further includes a memory configured to store a plurality of prior setpoints during respective prior plurality of periods of time, each of the prior plurality of periods of time being before the first period of time, wherein the processing circuitry is further configured to determine an indication of heart failure based, at least in part, on the first setpoint, the second setpoint, and the plurality of prior setpoints stored in memory.

[0135] Example 14: The system of any of examples 12-13, wherein the processing circuitry is further configured to: determine a value of cardiac motion of the heart based, at least in part, on a plurality of setpoints, the plurality of setpoints including at least the first setpoint and the second setpoint; and determine the indication of heart failure based on the determined value of cardiac motion.

[0136] Example 15: The system of example 14, wherein to determine the value of cardiac motion of the patient based, at least in part, on the plurality of setpoints, the processing circuitry is further configured to: determine a change between the plurality of setpoints; and determine the value of cardiac motion of the heart based, at least in part, on the change between the plurality of setpoints.

[0137] Example 16: The system of example 15, wherein to determine the change between the first setpoint and the second setpoint, the processing circuitry is further configured to: determine a difference between the plurality of setpoints; and determine the value of cardiac motion of the heart based, at least in part, on the difference between the plurality of setpoints.

[0138] Example 17: The system of any of examples 12-16, wherein the plurality of setpoints correspond to a predetermined pacing rate.

[0139] Example 18: The system of any of examples 12-17, wherein the sensor is a motion sensor.

[0140] Example 19: The system of any of examples 12-18, wherein processing circuitry is further configured to determine the indication of heart failure satisfies a heart failure threshold; and generate a remediation action in response to the determination that the indication of heart failure satisfies the heart failure threshold.

[0141] Example 20: The system of example 19, wherein the remediation action includes modifying a therapy.

[0142] Example 21: The system of any of examples 12-20, wherein the first setpoint is a first activity of daily living (ADL) setpoint and the second setpoint is a second ADL setpoint.

[0143] Example 22: A method includes determining one or more cardiac activity counts of a heart of a patient based on a motion signal based on cardiac motion; determining an indication of heart failure based on the one or more cardiac activity counts; and outputting information pertaining to the indication of heart failure to a device or network.

[0144] Example 23: The method of example 22, wherein determining one or more cardiac activity counts based on a motion signal includes: applying a filter to the motion signal; rectifying the filtered motion signal; and applying a discrete integration to the rectified filtered motion signal to determine a particular cardiac activity count of the one more cardiac activity counts.

[0145] Example 24: The method of example 23, wherein the filter is a 1 Hertz (Hz) to 10 Hz bandpass filter.

[0146] Example 25: The method of example 23, wherein the filter is a 10 Hertz (Hz) to 30 Hz bandpass filter. [0147] Example 26: The method of any of examples 23-25, wherein applying a discrete integration to the rectified filtered motion signal includes: applying the discrete integration for a period of time between 1.5 seconds to 2.5 seconds.

[0148] Example 27: The method of any of examples 22-26, the method further includes determining a value of a first resting cardiac activity count during a first period of time based on the one or more cardiac activity counts determined during the first period of time; determining a value of a second resting cardiac activity count during a second period of time based on the one or more cardiac activity counts determined during the second period of time, the second period of time being after the first period of time; and determining the indication of heart failure based on the first resting cardiac activity count and the second resting cardiac activity count.

[0149] Example 28: The method of any of examples 22-26, the method further includes determining a value of resting cardiac activity count during a period of time based on the one or more cardiac activity counts determined during the period of time; repeating determining a value of resting cardiac activity count for a plurality of time periods at a regular interval; storing the values of the respective resting cardiac activity counts to memory; determining the indication of heart failure based on the stored values of the resting cardiac activity counts.

[0150] Example 29: The method of example 27, the method further includes determining the indication of heart failure based on a difference between the value of the first resting cardiac activity count and the value of the second resting cardiac activity count.

[0151] Example 30: The method of example 28, the method further includes determining the indication of heart failure based on a correlation or regression of the values of the stored values of the resting cardiac activity counts.

[0152] Example 31: The method of any of examples 22-30, wherein a particular cardiac activity count of the one more cardiac activity counts corresponds to energy used by the heart during a period of time the particular cardiac activity count is determined. [0153] Example 32: The method of any of examples 22-31, the method further includes determining the indication of heart failure satisfies a heart failure threshold; and generating a remediation action in response to the determination that the indication of heart failure satisfies the heart failure threshold. [0154] Example 33: The method of example 32, wherein the remediation action includes modifying a therapy.

[0155] Example 34: The method of any of examples 22-33, wherein the wherein the motion signal comprises at least an accelerometer signal.

[0156] Example 35: A method includes determining a value of a parameter indicative of a workload of a heart of a patient based on a sensed signal via a sensor; determining a first setpoint based on a value of a parameter indicative of a workload of the heart during a first period of time; determining a second setpoint based on a value of a parameter indicative of a workload of the heart during a second period of time, the second period of time being after the first period of time; determining an indication of heart failure based, at least in part, on the first setpoint and the second setpoint; and outputting information pertaining to the indication of heart failure to a device or network.

[0157] Example 36: The method of example 35, the method further includes storing a plurality of prior setpoints during respective prior plurality of periods of time, each of the prior plurality of periods of time being before the first period of time; and determining an indication of heart failure based, at least in part, on the first setpoint, the second setpoint, and the stored plurality of prior setpoints.

[0158] Example 37: The method of any of examples 35-36, the method further includes determining a value of cardiac motion of the heart based, at least in part, on a plurality of setpoints, the plurality of setpoints including at least the first setpoint and the second setpoint; determining the indication of heart failure based on the determined value of cardiac motion.

[0159] Example 38: The method of example 37, wherein determining a value of cardiac motion of a patient based, at least in part, on the first setpoint and the second setpoint includes: determining a change between the first plurality of setpoints; and determining the value of cardiac motion of the heart based, at least in part, on the change between the plurality of setpoints.

[0160] Example 39: The method of example 38, wherein determining the change between the first setpoint and the second setpoint includes: determining a difference between the plurality of setpoints; and determining the value of cardiac motion of the heart based, at least in part, on the difference between the plurality of setpoints. [0161] Example 40: The method of any of examples 35-39, wherein the sensor is a plurality of electrodes.

[0162] Example 41: The method of any of examples 35-40, wherein the sensor is a motion sensor.

[0163] Example 42: The method of any of examples 35-41, the method further includes determining the indication of heart failure satisfies a heart failure threshold; and generating a remediation action in response to the determination that the indication of heart failure satisfies the heart failure threshold.

[0164] Example 43: The method of example 42, wherein the remediation action includes modifying a therapy.

[0165] Example 44: The method of any of examples 35-43, wherein the setpoints are an activity of daily living (ADL) setpoints.

[0166] It will be appreciated by persons skilled in the art that the present application is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the application, which is limited only by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: an implantable medical device (IMD) configured to be implanted in a patient, the IMD comprising a motion sensor configured to generate a motion signal based on cardiac motion over a period of time; and processing circuitry configured to: determine one or more cardiac activity counts of a heart of the patient based on the motion signal; determine an indication of heart failure based on the one or more cardiac activity counts; and output information pertaining to the indication of heart failure to a device or network.

2. The system of claim 1, wherein to determine cardiac activity counts based on the motion signal, the processing circuitry is further configured to: apply a filter to the motion signal; rectify the filtered motion signal; and apply a discrete integration to the rectified filtered motion signal to determine a particular cardiac activity count of the one more cardiac activity counts.

3. The system of claim 2, wherein the filter is a 1 Hertz (Hz) to 10 Hz bandpass filter.

4. The system of claim 2, wherein the filter is a 10 Hertz (Hz) to 30 Hz bandpass filter.

5. The system of any of claims 2-4, wherein processing circuitry is further configured to apply the discrete integration for a period of time between 1.5 seconds to 2.5 seconds.

6. The system of any of claims 1-5, wherein the processing circuitry is further configured to: determine a value of a first resting cardiac activity count during a first period of time based on the one or more cardiac activity counts determined during the first period of time; determine a value of a second resting cardiac activity count during a second period of time based on the one or more cardiac activity counts determined during the second period of time, the second period of time being after the first period of time; and determine the indication of heart failure based on the first resting cardiac activity count and the second resting cardiac activity count.

7. The system of claim 6, wherein the processing circuitry is further configured to determine the indication of heart failure based on a difference between the value of the first resting cardiac activity count and the value of the second resting cardiac activity count.

8. The system of any of claims 1-7, wherein a particular cardiac activity count of the one more cardiac activity counts corresponds to energy used by the heart during a period of time the particular cardiac activity count is determined.

9. The system of any of claims 1-8, wherein the processing circuitry is further configured to determine the indication of heart failure satisfies a heart failure threshold; and generate a remediation action in response to the determination that the indication of heart failure satisfies the heart failure threshold.

10. The system of claim 9, wherein the remediation action includes modifying a therapy.

11. A system comprising: an implantable medical device comprising: a sensor configured to detect a signal indicative of a workload of a heart of a patient; and therapy generation circuitry configured to deliver cardiac pacing to the heart; and processing circuitry configured to: determine a value of a parameter indicative of workload of the heart of the patient based on the detected signal; control the therapy generation circuitry to deliver the cardiac pacing at a pacing rate based on the value of the parameter and a predetermined relationship between values of the parameter and cardiac pacing rates; determine a first setpoint for the predetermined relationship based on a value of a parameter indicative of a workload of the heart during a first period of time; determine a second setpoint for the relationship based on a value of a parameter indicative of a workload of the heart during a second period of time, the second period of time being after the first period of time; determine an indication of heart failure based, at least in part, on the first setpoint and the second setpoint; and output information pertaining to the indication of heart failure to a device or network.

12. The system of claim 11, further comprising: a memory configured to store a plurality of prior setpoints during respective prior plurality of periods of time, each of the prior plurality of periods of time being before the first period of time, wherein the processing circuitry is further configured to determine an indication of heart failure based, at least in part, on the first setpoint, the second setpoint, and the plurality of prior setpoints stored in memory.

13. The system of any of claims 11-12, wherein the processing circuitry is further configured to: determine a value of cardiac motion of the heart based, at least in part, on a plurality of setpoints, the plurality of setpoints including at least the first setpoint and the second setpoint; and determine the indication of heart failure based on the determined value of cardiac motion.

14. The system of claim 13, wherein to determine the value of cardiac motion of the patient based, at least in part, on the plurality of setpoints, the processing circuitry is further configured to: determine a change between the plurality of setpoints; and determine the value of cardiac motion of the heart based, at least in part, on the change between the plurality of setpoints.

15. The system of any of claims 11-14, wherein the plurality of setpoints correspond to a predetermined pacing rate.