EP0906055A1

EP0906055A1 - An apparatus for detecting and determining the magnitude of intracardiac shunts

Info

Publication number: EP0906055A1
Application number: EP97925223A
Authority: EP
Inventors: Jiri Endrys
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-06-17
Filing date: 1997-06-16
Publication date: 1999-04-07
Also published as: JP2000512864A; WO1997048334A1; SE9602388D0

Abstract

The present invention relates to an apparatus (40) for detecting and determining the magnitude of intracardiac shunts by the use of thermodilution. Two thermodilution curves are measured from different parts of the heart. The presence of an intracardiac shunt is detected by comparing (48) the shapes of the measured thermodilution curves with the shape of thermodilution curves obtained from a heart without a shunt. To determine the magnitude of an intracardiac shunt the areas below the measured thermodilution curves are calculated (52). This area-information is used for calculation (52) of the cardiac output and then the magnitude of the shunt.

Description

AN APPARATUS FOR DETECTING AND DETERMINING THE MAGNITUDE OF INTRACARDIAC SHUNTS

Technical field of the invention. The present invention relates to an apparatus for detecting and determining the magnitude of intracardiac shunts by the use of thermodilution. Description of related art.

Intracardiac shunts are today normally detected by computing blood samples from different sites within the heart The differences m oxygen saturation indicate wether a shunt exists or not The method is also not particularly sensitive and is also prone to measurement errors, especially in patients with atrial septal defect . SU-A-1109124 describes a method for diagnosing of mtracardial blood shunt defects by introduction of a hypertonic sodium chloride solution into the high pressure heart chamber with subsequent registration of the moment at which it reaches the heart chamber with a lower pressure The electric blood resistance m the chamber with the lower pressure is measured before and after the introduction of the hypertonic sodium chloride solution and m the event of an electric blood resistance in the heart chamber, as compared with the initial resistance, a heart defect with pathological mtracardial blood shunt is diagnosed.

Summary of the invention

The present invention solves the problems noted above and provides an apparatus for detecting and determining the magnitude of intracardiac shunts by the use of thermodilution By using the known thermodilution technique two thermodilution curves are measured from different parts of the heart. The presence of an intracardiac shunt is detected by comparing the shapes of the measured thermodilution curves with the shape of thermodilution curves obtained from a heart without a shunt. If the compared shapes do not correspond to each other it indicates that an intracardiac shunt exists. To determine the magnitude of an intracardiac shunt the areas under the measured thermodilution curves are calculated. This area - information is used for calculation of the cardiac output, that is the volume of blood ejected by the heart per unit time, and then the magnitude of the shunt. Thermodilution is one of several different: techniques to determine cardiac output, but one advantage is that thermodilution is a rather simple and precise method.

Thermodilution is one common form of indicator dilution used to obtain cardiac output. With this technique, a thermodilution catheter is placed e.g. in the right part of the heart so that an injection port of the catheter is in the right atrium and a thermistor on the catheter is located downstream in the pulmonary artery. A bolus of cold saline is injected into the right atrium through the injection port where it mixes with the blood and produces a temperature change which is detected by the thermistor. From this, a thermodilution curve can be plotted, and the shape of the curve depends on the flow rate.

The apparatus for detecting and determining the magnitude: of intracardiac shunts by the use of thermodilution accordinςt to the present invention comprises means for measuring the temperature changes of the blood as a function of time for providing of two different thermodilution curves obtained from different parts of the heart. Then the thermodilution curves are digitized by a digitizing means, e.g. an A/D-converter. The digitized thermodilution curves are then stored in a memory unit connected to the digitizing means. The apparatus according to the present invention also comprises a comparison unit connected to the memory unit for comparing of the shapes of the measured thermodilution curves with the shapes of thermodilution curves obtained from a heart without a shunt. If the compared shapes do not correspond to each other this means that an intracardiac shunt exists. To the comparison unit a correction unit is connected for eliminating the influence of a left - to - right shunt (L-R shunt) on the thermodilution curve. This is done by extrapolation of the thermodilution curve. The apparatus according to the invention thus also comprises a calculation means connected to the correction unit for calculation in the first place of the areas under the thermodilution curves. In the second place the calculation means calculates, in dependance of the type of shunt, a left - to - right shunt or a right - to - left shunt, and in dependance of the type of heart defect, an atrial septal defect, ASD, a ventricular septal defect, VSD, or a patent ductus arteriosus, PDA, different combinations of cardiac outputs to finally determine the magnitude of the shunt.

By using the apparatus according to the present invention one provides an accurate and reliable way to detect and determine the magnitude of intracardiac shunts . The magnitude of intracardiac shunts is the most important parameter in deciding for surgical treatment of a heart .

The invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying illustrative drawings.

Brief description of the drawings.

Fig. 1 is a schematic sectional view of a human heart;

Fig. 2 is a plot of a thermodilution curve obtained for a heart without a shunt;

Fig. 3 is a plot of a thermodilution curve obtained for a heart with a left to right shunt (L-R shunt) ;

Fig. 4 is a plot of a thermodilution curve obtained for a heart with a right to left shunt (R-L shunt) ; and Fig. 5 is a schematic block diagram of an apparatus according to the present invention.

Detailed description of the preferred embodiment.

In figure 1 there is disclosed a schematic sectional view of a human heart. The heart is partitioned in a right half and a left half. The right half of the heart comprises the right ventricle RV, and the right atrium, RA. In a corresponding way the left half of the heart comprises the left ventricle, LV, and the left atrium, LA. In figure 1 there is also disclosed the inferior vena cava, IVC, which leads to the right atrium, RA, and the pulmonary artery, PA, which leads to the lungs. The pulmonary vein, PV, leads to the left atrium, LA, and the aorta, AO, leads the blood to "the rest of the body". There are three different types of heart defects which give rise to shunts, namely atrial septal defect, ASD, a hole in the wall between the right atrium RA, and the left atrium, LA, ventricular septal defect, VSD, a hole in the wall between the right ventricule, RV, and the left ventricule, LV, and patent ductus arteriosus (or coronary A-V fistula) , PDA, an abnormal connection between the aorta, AO, and the pulmonary artery, PA. The shunts are partitioned in L-R shunt, a left to right shunt (abnormal connection from the left to the right half of the heart) and R-L shunt, a right to left shunt (abnormal connection from the right to the left half of the heart) .

The principle upon which the thermodilution technique is based is that the change of heat of a substance is related to its mass and specific heat for a given change in temperature. For a static system, if two substances at different temperatures are mixed, the resulting temperature of the mixture will fall between the starting temperatures of the two substances. If the mass of one substance is unknown, it can be determined by equating at equilibrium the change on heat of the two substances and calculating the unknown mass from the resulting equation. When this principle is applied to a system of continuous flow, as in the heart and vasculature, a small amount of relatively cool substance (e.g. saline) is injected into and mixed with the blood, thereby yielding a time - temperature curve which may be sensed slightly downstream of the point at which the saline is injected into the system. The curve is referred to as the thermodilution curve, and the are below the thermodilution curve represents the sum of the instantaneous mixed temperatures at the sensing point. Normally the resulting time - temperature curve is reversed, so the curve is displayed as positive values.

Fig. 2 is a plot of thermodilution curve 10 obtained for a heart without a shunt, i.e. a healthy heart. The rising part of the curve indicates the cooling of the blood and the decay of the curve indicates the subsequent heating of the blood. Tie curve is characterized by an exponential decay.

Fig. 3 is a plot of a thermodilution curve 20 obtained for a heart with a left - to - right shunt (L-R shunt) , i.e. an abnormal connection from the left to the right half of the heart. If the curves of fig. 2 and fig. 3 are compared to each other it is apparent that the downslope of the curve m figure 3 follows another exponential track after a certain point, S in figure 3 where this point is situated at 56% of the peak value of the curve 20.

Fig. 4 is a plot of a thermodiluition curve 30 obtained for a heart with a right - to - left shunt (R-L shunt) , i.e. an abnormal connection from the right to the left half of the heart . This curve is recorded from a patient with an atrial septal defect, ASD, i.e. a hole m the wall between the right atrium, RA, (see fig. 1) and the left atrium, LA. As is apparent from fig. 4 "the ordinary" thermodilution curve is added with a R-L shunt wave 32.

To be able to record a thermodilution curve a catheter is inserted e.g. into a large vein and passed along the vein toward e.g. the right heart and through the right part of the heart to a short distance beyond. The catheter has an orifice cut to the outside of the catheter and liquid is injected at this orifice into the bloodstream from the far end of the catheter. Disposed in the catheter is one or two thermistors, placed at different places along the catheter. These catheters are well known m the medical field and, accordingly, are not shown or described m detail.

To be able to detect and determine the magnitude of intracardiac shunts with the apparatus according to the present ivention one have to record two different thermodilution curves . In dependance of the type of shunt and of the type of ^Ωart defect the catheter has to be placed m different sites hin the heart, i.e. cold saline is injected into different pidces and the thermo-probe (or thermo-probes) is measuring the temperature at different sites within the heart. Below follows a list of where to inject cold saline and where to place the thermo-probe (the thermo-probes) to provide the necessary information for the apparatus according to the present invention. Measurement of L-R shunt 1. Atrial septal defect (ASD) :

First curve : Injection of cold saline into right atrium (RA) or Superior vena cava (SVC) or Infenor vena cava (IVC) . Thermo-probe in the pulmonary artery (PA) -measures pulmonary blood flow (PBF=CO_R) .

Second curve : Injection of cold saline into the left ventricle (LV) . Thermo-probe in the aorta (AO) measures systemic blood flow (SBF=COJ L-R shunt = PBF - SBF (all in L/min) . 2.1. Patent ductus arteriosus (or cornary A-V fistula)

(PDA) ^•. Injection of cold saline into the left ventricle (LV) .

Thermo - probes: 1st in the descending aorta (DA) - measures PBF; 2nd in the pulmonary artery (PA) - measures L-R. 2.2. Ventricular septal defect (VSD) : First curve: Injection of cold saline into the right atrium (RA) . Thermo-probe in the pulmonary artery (PA) - measures PBF.

Second curve : Injection of cold saline into the left ventricle (LV) . Thermo-probe in the pulmonary artery (PA) - measures L-R. L-R shunt is calulated as the ratio:

^A _L-_R/A_PBF x 100 = L-R (in % of PBF) ; L-R (in L/min) = L-R (% of PBF) x PBF/100; SBF = PBF - L-R (all in L/min) where A_{L R} = Area of 2nd curve, A_PBF = Area of 1st curve. Measurement of R-L shunt.

In all defects, atrial septal defect, patent ductus arteriosus and ventricular septal defect, the same method of placing the catheter is used.

First curve: Injection of cold saline into the left ventricular (LV) . Thermo - probe in the aorta (AO) - measures systemic blood flow (SBF) .

Second curve : Injection of cold saline into the right atrium (FA) or superior vena cava (SVC) or infenor vena cava (IVC) . Thermo - probe in the aorta (AO) - measures R-L. R-L shunt is calculated as the ratio;

R-L (in % of SBF) = A_R_,,/ A_SBF xlOO R-L (in L/min) = R-L (% of SBF) x SBF/100 PBF=SBF - R-L (all m L/min) where A_R , = Area of 2nd curve, ^A _SBΓ = Area of 1st curve.

In figure 5 there is disclosed a schematic block diagram of an apparatus 40 according to the present invention. The apparatus 40 comprises a means 42 for measuring the temperature of the blood as a function of time The measuring means 42 receives thermo - probe - input from the thermo - probe (probes) m the catheter. The measuring means 42 must be able to receive two different thermo - probe - signals simultaneously if the catheter has two thermo - probes. The measuring means 42 outputs an analog signal, m the form of a thermodilution curve (see fig 2-4) , to a digitizing means 44 for digitizing the thermodilution curve (or curves) . The apparatus 40 also comprises a memory unit 46 connected to the digitizing means 44 for storing the digitized thermodilution curve The memory unit 46 is constructed to store at least two digitized thermodilution curves, because the information contained in two thermodilution is needed to be able to both detect and determine the magnitude of mfracardiac shunts A comparison unit 48 is connected to the memory unit 46 for comparing of the shapes of the measured thermodilution curves with the shape of thermodilution curves obtained from a heart without a shunt. If the compared shapes do not correspond to each other this indicates that an intracardiac shunt exists The apparatus 40 also comprises a correction unit 50 connected to the comparison unit 48 for eliminating the influence of a left to - right shunt (L-R shunt) (see fig. 3) on the thermodilution curve. If a left - to - right shunt exists m the heart the downslope of the curve 20 follows another exponential track after a certain point, S in fig 3 where this point is situated at 56% of the peak value of the curve 20 The correction unit 50 uses extrapolation for correction of the curve for the shunt flow. Two points are chosen on the thermodilution curve (see fig. 3) , one of which being point S, where the normal exponential portion of the curve is changed due to the shunt flow. The other point T is chosen on the normal, unchanged decaying portion of the curve at 79% of the peak value of the curve. The final portion of the curve, that is the curve to the right of point S in fig. 3, is then extrapolated by using an exponential decay, fitted to said two points T, S, giving the corrected "curve" 22. In this way the area below the curve, which is used e.g. for calculation of the cardiac output, CO, is corrected for the shunt flow. (See the equation below) . To the correction unit 50 a calculation means 52 is connected for calculation in the first place of the areas under the measured thermodilution curves and, when the shunt is a left - to - right shunt, for calculation in the second place of the cardiac output of the right half of the heart, CO_R, and (of the cardiac output of the left half of the heart, C0_L, and the magnitude of the left - to - right shunt) or the magnitude of the left - to - right shunt. When the shunt is a right - to - left shunt then the calculation unit in the second place calculates the cardiac output in the left half of the heart, C0_L, and the magnitude of the right - to - left shunt . The left - to - right shunt is defined as:

L-R shunt flow = SBF - PBF where PBF=C0_R; SBF = CO_L

The magnitude of the shunt is often expressed in percent, namely:

L-R%_SPF = (C0_L-C0_R)/C0_L

L-R%_PBF = (CO_L-CO_R) /CO_R The cardiac output, CO is given by the modified

Stewart-Hamilton equation as:

CO = (V* CJVT,) /A) * ( (S,*^ ) (/S_B*C_B) ) *60*C₁ where

V = injected volume (1) ; A = Area of thermodilution curve (°*S) ; T_B = Blood temperature (°C) ; T_: = Temperature of injected liquid (°C) ; S_j = Specific gravity of injected liquid; C_j = Specific heat of injected liquid; S_u = Specific gravity of blood; C_p = Specific heat of blood and C_τ = Correction factor for heating in the catheter of the injected liquid.

The magnitude of the different shunts can also be calculated as

L-R (in % of PBF) = A_lι._R/A_PBF*100

L-R (in l/min) = L-R(% of PBF) * PBF/100 where A, - _uH = Area of R - L curve and

A_SBF = Area of SBF curve .

The apparatus 40 also comprises a display unit 54 connected to the calculation means 52 and to the memory unit 46 The display unit 54 displayes plots of the measured thermodilution curves and the magnitade of the intracardiac shunt .

The digitizing means 44 can be a conventional A/D- converter 44. Although an exemplary embodiament of the invention has been shown and described, many changes, modifications and substitutions may be made by one having ordinary skill in the art without necessarily departing from the spirit and scope of this invention.

Claims

1. An apparatus (40) for detecting and determining the magnitude of intracardiac shunts by the use of thermodilution, wherein a cold liquid is injected e.g. in the right atrium and the resulting cooling and subsequent heating of the blood is measured, e.g., in the pulmonary artery, said apparatus (40) comprising:

- means (42) for measuring the temperature of the blood as a function of time for providing of two different thermodilution curves obtained from different parts of the heart;

- a means (44) connected to the measuring means (42) for digitizing of the thermodilution curves; - a memory unit (46) connected to the digitizing means

(44) for storing of the digitized thermodilution curves;

- a comparison unit (48) connected to the memory unit (46) for comparing the shapes of the measured thermodilution curves with the shape of thermodilution curves obtained from a heart without a shunt and if the compared shapes not corresponds to each other it indicates that an introcardiac shunt exists;

- a correction unit (50) connected to the corparison unit (48) for eliminating the influence of a left - to - right shunt (L-R shunt) on the thermodilution curve; - a means (52) connected to the correction unit (50) for calculation in the first place the areas below the thermodilution curves and, when the shunt is a left - to - right shunt, for calculation in the second place the cardiac output of the right half of the heart, CO_K, and (of the cardiac output of the left half of the heart, CO_L, and the magnitude of the left - to - right shunt) or the magnitude of the left - to - right shunt, and, when the shunt is a right - to - left shunt (R-L shunt) , for calculation in the second place of the cardiac output of the left half of the heart, CO_L, and the magnitude of the right - to - left shunt.

2. An apparatus (40) according to Claim 1, characterized in that the calculating means (52) is arranged to use of the modified Stewart-Hamilton equation for calculation of the cardiac output, CO: CO= (V* (T_B-T_T) /A) * ( (S_τ*C_r) / (S_B*C_B) ) *60*C_T where

V - injected volume (1) ; A = Area of thermodilution curve (°C*s) ; T_B = Blood temperature (°C) ; T_x = Temperature of injected liquid (°C) ; S_τ = Specific gravity of injected liquid; C_t = Specific heat of injected liquid; S_B = Specific gravity of blood; C_B = Specific heat of blood and C_τ = Correction factor for heating in the catheter of the injected liquid.

3. An apparatus (40) according to Claim 2, characterized in that the correction unit (50) is arranged to extrapolate the thermodilution curve to eliminate the influence of a left - to - right shunt .

4. An apparatus (40) according to Claim 3, characterized in that the correction unit (50) is arranged to perform the extrapolation by the use of two different points (T,S) on the measured thermodilution curve, wherein the first point (T) is chosen at a predetermined fraction of the peak value of the measured thermodilution curve and the second point (S) is chosen at another point on the thermodilution curve where the decay of the curve not deviates from the exponential decay of a thermodilution curve for a heart without a shunt, wherein the extrapolation is performed by using an exponential decay, adapted to said two points (T,S) .

5. An apparatus (40) according to Claim 4, characterized in that the first point (T) is chosen at 79% of the peak value of the measured thermodilution curve.

6. An apparatus (40) according to Claim 5, characterized in that the calculating means (52) for calculating the magnitudes of the different shunts makes use of the equations. L-R%C0, = (CO_L - COJ /CO,, L-R%CO_R = (C0_L - CO_R)/CO_R L-R%CO_R = A_L__R/A_ΓOR xlOO R-L%CO_L = A_R__L/A_C0I, x 100 where A are different areas for different thermodilution curves

7. An apparatus (40) according to Claim 6, characterized in that the digitizing means (44) is an A/D converter (44) .

8. An apparatus (40) according to any of the preceding Claims, characterized in that the apparatus (40) also comprises a display unit (54) for displaying plots of the measured thermodilution curves and the magnitude of the intracardiac shunt .