Cardiac Device, Method and Computer Program Product

Abstract

A cardiac device is provided including a measuring electrode, a signal-processing unit and a post-processing unit. The measuring electrode is adapted to be positioned within the blood pool of a human or an animal heart, in order to measure a depolarization-signal. The signal-processing unit is connected to the measuring electrode and is adapted to remove signal components with frequencies lower than a cut-off frequency from the measured depolarization-signal. The post-processing unit is connected to the signal-processing unit and is adapted to determine, based on the Brody effect, a measure for a ventricular volume of the heart based on the modified depolarization-signal. Furthermore, a method for the determination of a measure for a ventricular volume of a heart and a computer program product for performing the steps of this method are provided.

Claims

1. A cardiac device comprising at least one measuring electrode adapted to be positioned within the blood pool inside or in close proximity of a human or an animal heart, in order to measure an electric depolarization-signal of the heart, a signal-processing unit which is connected to the at least one measuring electrode and which is adapted to remove signal components with frequencies lower than a certain cut-off frequency from the measured depolarization-signal, in order to provide a modified depolarization-signal, and a post-processing unit which is connected to the signal-processing unit and which is adapted to determine, based on the Brody effect, a measure for a ventricular volume of the heart based on the modified depolarization-signal.

2. The cardiac device of claim 1, wherein the signal-processing unit is adapted to remove the signal components from the measured depolarization-signal the measured depolarization-signal, in order to obtain a low-pass filtered depolarization-signal, and subtracting the low-pass filtered depolarization-signal from the measured depolarization-signal.

3. The cardiac device of claim 1, wherein the cut-off frequency is between 0.03 and to 0.04 Hz, in particular between 0.015 and 0.05 Hz.

4. The cardiac device of claim 1, wherein the cardiac device comprises a plurality of measuring electrodes and is adapted to select a subset of these measuring electrodes to measure the depolarization-signal of the heart.

5. The cardiac device of claim 1, wherein the cardiac device is arranged completely inside a human or animal body.

6. The cardiac device of claim 1, wherein the cardiac device comprises at least one battery which is preferably used to provide electrical energy to the signal-processing unit and/or to the post-processing unit, and wherein the at least one measuring electrode is adapted to measure the depolarization-signal with respect to an electric potential defined by the at least one battery.

7. The cardiac device of claim 1, wherein the at least one measuring electrode is adapted to measure the depolarization-signal with respect to an electric potential defined by one or several reference electrodes being positioned within the blood pool inside or in close proximity of a human or an animal heart.

8. The cardiac device of claim 1, wherein the post-processing unit is adapted to determine the measure for the ventricular volume of the heart on the peak amplitude between the zero-line or isoelectric line and a maximum absolute value of the modified depolarization-signal or based on the peak-to-peak amplitude between a minimum value and a maximum value of the modified depolarization-signal.

9. The cardiac device of claim 1, wherein the cardiac device is a monitoring device and preferably additionally comprises an indicator device, in order to indicate a state of the heart on the determined measure for the ventricular volume of the heart.

10. The cardiac device of claim 1, wherein the cardiac device is an artificial cardiac pacemaker or a cardioverter-defibrillator (IDC) comprising a controller for regulating the heart rate of the heart based on the determined measure for the ventricular volume of the heart.

11. The cardiac device of claim 1, wherein the cardiac device is a biomedical apparatus, in particular a ventricular assist device (VAD), for pumping blood through a secondary intra- or extracorporeal blood circuit and comprises a blood pump pumping blood, an inlet duct connected to the blood pump, for being inserted into a patient's circulatory system, in order to guide blood of the patient to the blood pump, an outlet duct connected to the blood pump, for being inserted into the patient's circulatory system, in order to guide blood from the blood pump back to the patient's circulatory system, and a controller for regulating the power of the blood pump based on the determined measure for the ventricular volume of the heart.

12. The cardiac device of claim 11, wherein the controller is configured to regulate the power of the blood pump based on the following linear function:
PW.sub.des=(EDV(t)−EDV.sub.0).Math.k.sub.prsw, in which PW.sub.des(t) denotes the desired pump work per heartbeat at a certain time t and EDV(t) an estimate for the end-diastolic volume of the heart determined based on the determined measure for the ventricular volume of the heart and in which the two parameters EDV.sub.0 and k.sub.prsw denote the end-diastolic volume at which the desired pump work is zero and the gain of the pump work relative to the estimated EDV(t), respectively.

13. The cardiac device of claim 11, wherein the at least one measuring electrode is arranged on the inlet duct, in particular at an open end of the inlet duct, of the biomedical apparatus.

14. The cardiac device of claim 1, additionally comprising at least one pressure sensor adapted to be positioned inside or in close proximity of the heart, wherein the post-processing unit is adapted to determine the measure for the ventricular volume of the heart based on a combination of the modified depolarization-signal and of a value measured by the pressure sensor.

15. A method for the determination of a measure for a ventricular volume of a human or an animal heart, in particular by means of a cardiac device as claimed in claim 1, the method comprising receiving a depolarization-signal measured by means of at least one measuring electrode positioned within the blood pool inside or in close proximity of the heart, modifying the depolarization-signal by removing signal components with frequencies lower than a certain cut-off frequency from the measured depolarization-signal, determining, based on the Brody effect, a measure for the ventricular volume of the heart based on the modified depolarization-signal, in particular based on the peak amplitude between the zero-line or isoelectric line and a maximum value of the modified depolarization-signal or on the peak-to-peak amplitude between a minimum value and a maximum value of the modified depolarization-signal.

16. The method as claimed in claim 15, wherein the determined measure for the ventricular volume of the heart used for regulating the power of a blood pump of a biomedical apparatus, in particular of a ventricular assist device (VAD) for pumping blood through a secondary intra- or extracorporeal blood circuit.

17. A computer program product directly loadable into the internal memory of a digital computer, comprising software code portions for performing the steps of claim 15, when said product is run on a computer.

Description

SHORT DESCRIPTION OF THE FIGURES

[0067] Preferred embodiments of the invention are described in the following with reference to the drawings, which only serve for illustration purposes, but have no limiting effects. In the drawings it is shown:

[0068] FIG. 1 a schematic cross-sectional view of a heart with preferred positions of the measuring electrodes;

[0069] FIG. 2 a schematic view of a control unit for controlling an inventive cardiac device according to a preferred embodiment;

[0070] FIG. 3 a graph of a time sequence similar to the QRS-complex of an IEMG of a possible modified depolarization-signal as provided by a signal-processing unit of an inventive cardiac device;

[0071] FIG. 4 a schematic diagram of a signal-processing unit of an inventive cardiac device according to a preferred embodiment; and

[0072] FIG. 5 a schematic view of a cardiac device according to the invention in the form of a ventricular assist device (VAD), implanted in the heart of a patient.

DESCRIPTION OF THE INVENTION

[0073] FIGS. 1 to 5 show preferred embodiments of the inventive cardiac device and of the inventive method for determining a measure for a ventricular volume of a human or an animal heart.

[0074] FIG. 1 shows a cross-sectional view of a heart 1 which in this case is a human heart. Within the heart 1, preferred locations for positioning one or several measuring electrodes 3, in particular (quasi-)unipolar electrodes, of the inventive cardiac device are shown. The electrodes 3 for measuring the depolarization-signal are preferably arranged inside the left ventricle 11 or the right ventricle 12. In certain embodiments and/or depending on the patient to be treated, the electrodes 3 can alternatively or additionally also be positioned in the left atrium 13 or the right atrium 14. It would basically even be possible to arrange the electrode(s) 3 in the aorta 21, in the inferior vena cava 22 or in the superior vena cava 23, as long as the electrode is in close proximity of the heart, in order to be able to measure the Brody effect.

[0075] In order to avoid that the depolarization-measurement result is impaired by local (partial) depolarization effects occurring in the cardiac muscle 15, the electrodes 3 are arranged within the blood pool 16 and preferably distant from the endocardium 17. Thus, the electrodes 3 are preferably completely surrounded by the blood streaming through the atria 13, 14 and the ventricles 11, 12 of the heart 1. The arrangement of the electrodes 3 within the blood pool 16 is preferably such that they are not contacted by the endocardium 17 during the motion of the heart 1. A preferred control unit for controlling an inventive cardiac device according to a preferred embodiment is schematically shown in FIG. 2.

[0076] A signal measurement and processing unit 41 is connected to one or several measuring electrodes 3 located inside or in close proximity of the heart 1. The control unit and, thus, the signal measurement and processing unit 13 are as a whole located outside of the heart, but preferably within the body of a patient. The signal measurement and processing unit 41 is adapted for data acquisition. For this purpose, a depolarization-signal measured by at least one electrode 3 is received by the signal measurement and processing unit 41 and modified such, that the Brody effect can be measured from a provided modified depolarization-signal 42, i.e. that a measure for the ventricular volume of the heart 1 can be determined based on the modified depolarization-signal 42. The modification of the measured depolarization-signal as carried out by the signal measurement and processing unit 41 is explained in more detail further down with respect to FIG. 4. Thus, the modified depolarization-signal 42 represents the output signal of the signal measurement and processing unit 41.

[0077] The modified depolarization-signal 42 is sent via a wireless connection 42a or via a cable connection 42b from the signal measurement and processing unit 41 to a depolarization amplitude detection unit 43. The depolarization amplitude detection unit 43 is adapted to first identify a time sequence that resembles a QRS-complex of an IEMG within the received data stream of the modified depolarization-signal 42 and to then detect the depolarization amplitude within each of the identified time sequence. The detection of the depolarization amplitude as carried out by the depolarization amplitude detection unit 43 is explained in more detail further down with respect to FIG. 3. The detected depolarization amplitude 44 is then transmitted by the depolarization amplitude detection unit 43 in a corresponding data stream to a ventricular volume determination unit 45.

[0078] According to the Brody effect, there is a functional relationship between the amplitude 44 and the (left) ventricular end-diastolic volume of the heart 1. This functional relationship is used by the ventricular volume determination unit 45 to determine a measure 46 for the ventricular volume of the heart 1 based on the amplitude 44 as provided by the depolarization amplitude detection unit 43. Thus, the received amplitude 44 is converted by the depolarization amplitude detection unit 43 to a measure 46 for the ventricular volume, in particular for the left ventricular end-diastolic volume of the heart 1. In a preferred embodiment, a linear relationship, negative or positive depending on the electrode position, between the detected depolarization amplitude 44 and the left ventricular end-diastolic volume of the heart 1 is applied by the depolarization amplitude detection unit 43. Thus, the output signal of the depolarization amplitude detection unit 43 is the measure 46 for the ventricular volume.

[0079] The measure 46 for the ventricular volume is transmitted from the depolarization amplitude detection unit 43 to an indicator device 47 and/or to a blood pump controller 48.

[0080] The indicator device 47 serves for monitoring purposes, e.g. if the cardiac device is a monitoring device. For this purpose, the indicator device 47 which is preferably arranged inside the body of the patient can for example comprise an acoustic signal generator. In a particularly preferred embodiment, however, the indicator device 47 can be an external device to which an alarm signal and/or data concerning the state of the heart 1 can be sent from a transmission unit of the cardiac device. The transmission to the external device can be carried out wirelessly or via a cable connection. The external device is preferably located outside of the patient's body and can be formed for example by a personal computer, a laptop, a smart phone or a smart watch. The transmission unit is preferably adapted to effect data transmission upon request, e.g. from a clinician or from the patient, and/or self-triggered as a push-transmission, e.g. when detecting a special event, such as an excess of the end-diastolic volume over a certain threshold or a complete emptying of the ventricular volume, and/or after certain time intervals.

[0081] The blood pump controller 48 can be part of a biomedical apparatus, in particular a ventricular assist device (VAD), for pumping blood through a secondary intra- or extracorporeal blood circuit. In such a biomedical apparatus, the blood pump controller 48 serves to regulate the power, in particular the output power of the blood pump which is used for pumping the blood through the secondary intra- or extracorporeal blood circuit. The blood pump controller 48 can particularly be used to regulate the speed, in particular the rotational speed or the frequency of pulsation, of the blood pump. The integration of the blood pump controller 48 in a VAD will be explained in more detail further down with respect to FIG. 5.

[0082] FIG. 3 shows a graph with a segment of a possible modified depolarization-signal 5 as provided by the signal measurement and processing unit 41. Thus, the modified depolarization-signal 5 as shown in the graph of FIG. 3 can particularly correspond to the modified depolarization-signal 42 as shown in FIG. 2.

[0083] The modified depolarization-signal 5 as shown in FIG. 3 contains a QRS-like complex 52 which is the result of the electrical excitation of the heart 1 during each cardiac cycle. The electrical excitation can be initiated by the heart 1 itself, i.e. naturally, or artificially by e.g. a cardiac pacemaker. The QRS-like complex 52 is represented in FIG. 3 with respect to an isoelectric line 51, i.e. the base line of the modified depolarization-signal 5. The QRS-like complex 52 comprises an R-wave 53 attributed to the depolarization of the left ventricle 11 of the heart 1. For determining a measure for the ventricular volume of the heart, e.g. by means of the ventricular volume determination unit 45, preferably the peak-to-peak amplitude 55 is used. The peak-to-peak amplitude 55 concerns the amplitude between a minimum value of the QRS-like complex 52, in particular the absolute minimum value of the QRS-like complex 52, and a maximum value of the QRS-like complex 52, in particular the absolute maximum value of the QRS-like complex 52. The maximum and/or minimum values of the QRS-like complex 52 are usually part of the R-wave 53. Alternatively, it is also possible to use the peak amplitude 54 for determining the measure for the ventricular volume of the heart 1. The peak amplitude 54 is measured between the isoelectric line 51 and a maximum absolute value of the QRS-like complex 52, in particular of the R-wave 53.

[0084] FIG. 4 shows a schematic diagram of a possible and preferred signal-processing unit of an inventive cardiac device. The signal-processing unit as shown can for example represent a part of the signal measurement and processing unit 41 as shown in FIG. 2.

[0085] As shown in FIG. 4, an input signal 61, i.e. the measured depolarization-signal, is transmitted from the one or several electrodes 3 to a low-pass filter 62. The low-pass filter 62 according to the embodiment as shown is a 2.sup.nd-order Sallen-Key low-pass filter with 47 μF (10%) capacitors and 100 kΩ (1%) resistors and having a cut-off frequency of 0.034 Hz.

[0086] From the low-pass filter 62, the filtered signal is guided, via a buffer 64, to the inverted input pin of an amplifier 66. In parallel thereto, the measured depolarization-signal is guided, via another buffer 63, from the at least one electrode 3 to the non-inverted input pin of the amplifier 66. In the current embodiment, a LM358 low power dual operational amplifier of Texas Instruments Inc. has been employed. In the amplifier 66, the low-pass filtered depolarization-signal is subtracted from the measured depolarization-signal, in order to suppress signal components which are affected by instabilities of the electric reference potential or ground (GND). The at least one electrode 3 can therefore be regarded as a unipolar electrode. Due to the use of the amplifier 66, a high input impedance of the signal-processing unit is achieved.

[0087] In cases where more than one electrode 3 is used for measuring the depolarization-signal, one or several further input channels 65 can be provided that are connected to the signal-processing unit between the low-pass filter 62 and the buffer 62.

[0088] The output of the amplifier 66 is wired to a high-pass filter 67 and to a low-pass filter 68 which are arranged in series. The high-pass filter 67 has a cut-off frequency of 0.015 Hz and serves to attenuate offsets in the depolarization-signal. The high-pass filter 67 comprises 47 μF (10%) capacitors and 220 kΩ (1%) resistors. The low-pass filter 68 which is realized as 2.sup.nd-order Sallen-Key filter with 27 kΩ (1%) resistors and 10 nF (5%) capacitors has a cut-off frequency of 590 Hz. The low-pass filter 68 serves to suppress high frequency noise and attenuate signal components close to and above the Nyquist-frequency of 1 kHz.

[0089] From the low-pass filter 68, the signal is then guided to the non-inverted input pin of a further amplifier 69. The inverted input pin of the amplifier 69 is connected to the ground (GND) 70. Thus, the amplifier 69 serves to amplify the depolarization-signal. From the amplifier 69, the signal is output in the form of output signal 71. The output signal 71 can particularly correspond to the modified depolarization-signal 42 or 5 as shown in FIGS. 2 and 3, respectively.

[0090] The ground 70 is used as the ground for both the amplifier 66 and the amplifier 69.

[0091] The output signal 71 of the signal-processing unit can then be forwarded to a data acquisition unit 73 of a controller 72. The controller 72 can particularly correspond to the blood pump controller 48 as shown in FIG. 2.

[0092] In FIG. 5, an embodiment of a biomedical apparatus for pumping blood of a human or an animal patient through a secondary intra- or extracorporeal blood circuit is shown. The apparatus of this embodiment is a Ventricular Assist Device (VAD) 8 used to partially or completely replace the function of the heart 1 of a patient with heart failure.

[0093] The VAD 8 comprises a blood pump 83, which can be a pneumatically or electrically actuated pulsatile volumetric pump, or an axial or centrifugal turbodynamic pump with classical contact bearings, with a magnetically levitated rotor or with a blood-immersed bearing or a percutaneous pump. A large variety of pumps of these kinds and suited for being used in a VAD are known to the person skilled in the art.

[0094] Connected to the blood pump 83 is an inlet duct 81 having an inlet cannula 82, which has an open end being inserted into the left ventricle 11 in the region of the apex of the heart 1. The inlet cannula 82 serves to guide blood from the inside of the left ventricle 11 to the blood pump 83. Due to the pumping action of the blood pump 83, the blood is drawn through an inlet opening located at the open end of the inlet cannula 82 into the inlet duct 81 and to the blood pump 83.

[0095] In direction of the blood stream, an outlet duct 84 is connected to the blood pump 83 on the opposite side relative to the inlet duct 81. The outlet duct 84 serves to guide the blood from the blood pump 83 back to the patient's circulatory system. To this end, the outlet duct 84 is inserted into the aorta 21 of the patient.

[0096] The inlet duct 81, the blood pump 83 and the outlet duct 84 together constitute a secondary blood circuit, which is preferably located completely inside the body of the patient. The blood streaming through this secondary blood circuit originates from the left ventricle 11 and streams into the aorta 21. Within the secondary blood circuit, the blood is pumped by the blood pump 83 in the direction towards the aorta 21. Thus, the blood pump 83 supports the function of the (failed) heart 1.

[0097] The output power by which the blood is pumped into the outlet duct 84 by the blood pump 83 is regulated by a controller 85. The controller 85 can particularly correspond to the controller 72 as shown in FIG. 4 and/or to the blood pump controller 48 as shown in FIG. 2. The controller 85 is directly connected to a signal-processing unit 87 which can particularly correspond to the signal-processing unit as shown in FIG. 4. The signal-processing unit 87 which is connected to a plurality of electrodes 3 is preferably contained together with the controller 85 and a battery 10 in a common housing. The housing is preferably arranged within the patient's body and can be directly attached to the blood pump 83. The signal-processing unit 87 is also connected to a pressure sensor 86.

[0098] The plurality of electrodes 3 and the pressure sensor 86 are attached to the inlet cannula 82 in the region of its open end. Thus, the electrodes 3 and the pressure sensor 86 are located centrally within the left ventricle 11. In order to avoid a contact of the electrodes with the cardiac muscle 15, some or all of the electrodes 3 can be suitably shielded, e.g. by a stiff net structure, and/or be arranged in e.g. a recess provided on the inlet cannula 82. In the present embodiment, commonly used pacemaker electrodes (Biotronik 25539254 IS-1BI) have been used for the electrodes 3. The middle potential of the battery 10 is here used as the ground 70 (see FIG. 4) of the signal-processing unit 87.

[0099] The controller 85 is able to receive signals from the electrodes 3 and the pressure sensor 86 via the signal-processing unit 87 and is able to communicate with the blood pump 83, in order to provide a closed-loop control for the blood pump 83. The controller 85 and/or the signal-processing unit 87 can particularly be represented by an integral circuit and preferably comprise at least one data storage module. The regulation of the power of the blood pump 83 by the controller 85 is based on the determination of a measure, such as the measure 46 shown in FIG. 2, for the volume of the left ventricle 11 at end-diastole. In order to obtain a measure for the inner ventricular volume for regulating the power of the blood pump 83, the depolarization-signal is measured by means of the quasi-(unipolar) electrodes 3. These measurements can be combined by the controller 85 with measurements carried out by means of the pressure sensor 86.

[0100] Based on the measure for the end-diastolic volume of the heart 1, the desired stroke work (PW.sub.des) of the blood pump 83 per heartbeat is calculated by the controller 85 according to the concept of preload recruitable stroke work (PRSW), as described in WO 2014/173527. Thus, the regulation of the power of the blood pump 83 by means of the controller 85 is based on the theory of venous return (Guyton A C, Hall J E. Textbook of Medical Physiology, 12th Edition. Saunders W B Co, 2010.) and the Frank-Starling law of the heart. This model states that the stroke work of the left ventricle 11 increases linearly with the end-diastolic volume EDV. Since the output (stroke work) of the heart 1 is proportional to the input (end-diastolic volume EDV), the PRSW can be viewed as a proportional controller of the heart 1. Hence, the controller 85 imitates the PRSW by proportionally adjusting the power of the blood pump 83 based on the determined measure for the EDV.