SYSTEM FOR MEASURING CARDIOGRAPHIC IMPEDANCE FOR CONTROLLING A HEART PUMP.

Description

[0001] The present invention relates to a cardiographic impedance measurement system.

[0002] It finds a particularly interesting application in the field of implanted cardiac assist devices.

[0003] Impedance cardiography (IC) is a technique well known to those in the profession.

[0004] Variations in blood volume within the heart chambers and, less commonly, the vascular system, lead to variations in thoracic and / or myocardial bioimpedance. Impedance cardiography allows these variations to be measured and the results displayed as a curve over time and during the cardiac cycle (diastole and systole).

[0005] More specifically, impedance cardiography allows for the monitoring and measurement of variations in stroke volume and diastolic filling volume of the patient's right or left ventricle using a primary dipole, known as the transmitting dipole. The patient's body is then electrically mapped by injecting a fixed-amplitude, subthreshold current lasting from 5 to 30 µs. The pulse duration is variable and follows Lapicque's law, which is well-known to those skilled in the art.

[0006] The current can also be injected in series of pulses (from 1 to n) with the same characteristics described above, consecutively. A second dipole, called the receiver dipole, is used to measure the voltage across the rib cage; this dipole can be attached either inside the body or to the skin surface. This dipole can also be attached to the surface of the myocardium if one wishes to focus on variations in blood volume within the heart chambers for greater accuracy. Body or myocardial voltage changes according to blood flow because blood and tissues have different electrical conductivities.

[0007] The voltage across the terminals of the receiving dipole allows us to calculate the impedance between the two dipoles.

[0008] Impedance monitoring is particularly useful for monitoring heart failure in patients, as heart failure leads to pathological dilation of the heart chambers, impairing the heart's contractile function. This monitoring provides initial indications of the patient's hemodynamic status.

[0009] We are familiar with document FR3103709B1 describing an implantable system for measuring pre-ejection period from cardiographic impedance. This system comprises two separate dipoles for measuring cardiographic impedance.

[0010] We are also familiar with document FR3103697A1, which describes implantable systems that also include two separate dipoles for measuring cardiographic impedance. The implanted systems may include, on the one hand, an automatic defibrillator or a loop recorder, and on the other hand, a leadless pacemaker capsule.

[0011] US patent 2013 / 066142 A1 relates to a device comprising a cardiac assist pump designed to connect the corresponding ventricle of a heart to the corresponding artery, and to pump blood from the corresponding ventricle to the corresponding artery. The described device is also capable of measuring cardiac impedance.

[0012] The present invention aims at a new cardiographic impedance measurement system that is more efficient than prior art systems.

[0013] Another objective of the invention is an integrated cardiac assistance system.

[0014] At least one of the aforementioned objectives can be achieved with a Cardio-Impedance measurement system that includes: at least one first pair of electrodes having a first electrode and a second electrode; the first electrode being connected to a generator configured to generate an excitation signal, a detector to detect the excitation signal, a processing unit configured to determine the Cardio-Impedance from the detected excitation signal.

[0015] The system according to the invention further comprises an implantable heart pump, and the second electrode is made up of a metallic part of this heart pump.

[0016] An excitation signal, also referred to as a cardiac electrical activation signal, is understood to be a transmitting signal intended to be subsequently detected after undergoing disturbances.

[0017] With the system according to the invention, a cardiographic impedance measurement is carried out advantageously using a metallic part of a cardiac pump as a reference for the electrodes used.

[0018] Preferably, a cardiac pump according to the invention is designed to be disposed wholly or partially inside a ventricle. The metallic part is preferably located inside the ventricle of the heart.

[0019] In operation, we thus take advantage of the presence of the heart pump in the intraventricular space to obtain highly accurate measurements.

[0020] The electrodes, for example in the form of rings, are designed to be screwed or sutured onto a wall of the heart, specifically the wall of a ventricle in which the heart pump is installed. However, other arrangements are possible, such as electrodes placed on the wall of one ventricle and a heart pump located inside the other ventricle.

[0021] During operation, impedance measurements effectively account for the distance between the ventricle wall and a reference point positioned inside the ventricle. The measurements are more precise and more sensitive to wall movements due to the specific electrode placement.

[0022] Advantageously, for each pair of electrodes, one electrode is intended to be positioned on the surface of the myocardium and another electrode inside the ventricle (right or left).

[0023] The metallic part of the heart pump thus serves as a ground for impedance measurements.

[0024] The first pair of electrodes may be a lead from a pacemaker.

[0025] Cardiographic impedance measurement thus makes it possible to manage the rotation speeds of an intracardiac turbine according to the volume of the cavity in which the turbine (or pump) is positioned and according to the cardiac phase in which the impedance measurement is carried out (in diastole or in systole).

[0026] According to an advantageous embodiment of the invention, the generator can be a current generator, and the detector can be a voltage detector connected between the first electrode and the second electrode.

[0027] In this first embodiment, known as bipolar, the first electrode can be supplied with a constant amplitude current, and the voltage between this first electrode and the metallic part of the heart pump can be measured. The detected voltage allows the cardiographic impedance to be calculated according to principles known to those skilled in the art.

[0028] According to another advantageous embodiment of the invention, the system may further comprise a second pair of electrodes having a third electrode and a fourth electrode; the fourth electrode being identical to the second electrode used as a reference electrode. According to the invention, the generator is a current generator and the detector is a voltage detector connected between the third electrode and the second electrode.

[0029] Current is injected via the second electrode and the voltage is collected via the third electrode to avoid any possible interference between the transmitter and the receiver.

[0030] According to another advantageous embodiment of the invention, the system may further comprise a second pair of electrodes having a third electrode and a fourth electrode; the fourth electrode being constituted by said metallic part of the heart pump. According to the invention, the generator may then be a voltage generator connected to the first pair of electrodes and the detector may be a voltage detector connected to the second pair of electrodes.

[0031] In particular, a pair of transmitting electrodes is thus planned, consisting of one pole on the myocardium and a metallic part of the pump, and a second pair of receiving electrodes consisting of a second pole on the myocardium and a metallic part of the pump).

[0032] In particular, the metallic part used in all embodiments can be a non-moving metallic part of the pump.

[0033] In this second embodiment, known as tripolar, the first pair is supplied with a time-varying signal with a constant peak amplitude, and a voltage is detected on the second pair; the two pairs have a common reference, which is the metallic part of the heart pump. Preferably, the variable signal emitted by the first electrode obeys Lapicque's law, known to those skilled in the art, so as not to artificially stimulate the patient's heart.

[0034] According to one embodiment of the invention, the processing unit can be configured to determine a change in the volume of the heart or a movement of a heart wall.

[0035] Calculating the impedance then allows us to deduce the variations in the volume of the core, in particular in relation to a reference volume, and the movements of the wall.

[0036] According to a preferred embodiment, for at least one cycle of cardiac activity, the processing unit is configured to determine: an instant t1 corresponding to the beginning of a ventricular depolarization of a cycle of cardiac activity, the instant t1 being obtained from a local electrogram of ventricular activation an instant t2 corresponding to the opening of the aortic valve, the instant t2 being obtained by impedance measurement by identifying the minimum value of impedance or the beginning of the positivity of the derivative of the impedance with respect to time, an instant t3 corresponding to the aortic closure, the instant t3 being obtained by impedance measurement by identifying a maximum in an impedance variation curve or by deduction from an instant t4, an instant t4 corresponding to the beginning of ventricular filling, the instant t4 being obtained by impedance measurement by identifying the beginning of the negativation of the derivative of the impedance with respect to time.

[0037] For example, time t1 is obtained from a local electrogram of ventricular activation detected by the dipole placed on the surface of the myocardium opposite the ventricle concerned (right or left).

[0038] The time t2 is obtained using a system comprising a bipolar probe which can be the dipole placed on the myocardium, and an acquisition chain equipped for example with an amplifier, filter and a microprocessor.

[0039] The time t3 can be deduced from t4 by subtracting from the time t4 a predetermined value or one calculated by ultrasound.

[0040] A bipolar epicardial probe can be used to generate the electrogram. This probe allows the ventricular rhythm to be monitored. It may be a pacemaker lead.

[0041] The system according to the invention makes it possible to identify remarkable moments in the heart rhythm.

[0042] Advantageously, the processing unit can be configured to determine, for example in real time or on a regular basis, control parameters of the heart pump.

[0043] The system according to the invention provides valuable real-time information on ventricular volume. This information is important because if a patient drinks little, ventricular volume decreases, blood volume decreases, and reducing the heart's pumping speed is part of the therapy to avoid exacerbated and potentially harmful ventricular wall suction. Conversely, if ventricular volume is found to increase, it may be necessary to increase the heart's pumping speed to increase the blood flow ejected during systole (ventricular contraction), thus causing ventricular overload that can induce pulmonary edema.

[0044] The system according to the invention makes it advantageous to use data on ventricular volume variation to effectively control the heart pump. This involves both the instantaneous volume, allowing for real-time or delayed control of the heart pump, and an average volume estimated over several cardiac cycles.

[0045] Advantageously, the processing unit can be configured to modulate, for example in real time or at regular intervals, the operating cycles of a cardiac pump motor based on variations in heart volume or wall motion, with each cycle comprising at least a low and a high pump speed. In other words, cardiographic impedance measurement is used to control the cardiac pump.

[0046] In addition to all of the above, the processing unit can be configured to modulate at least one of the following control parameters: the duration of the transition from low pump speed to high pump speed, for example during the electro-mechanical delay, the duration of the transition from high pump speed to low pump speed, for example during the isovolumic relaxation phase, the duration of maintaining high pump speed, for example during the systolic ejection time, the duration of maintaining low pump speed, for example during the diastolic phase of ventricular filling, the value of the high pump speed, called systolic speed, the value of the low pump speed, called diastolic speed.

[0047] Impedance variations are considered to be proportional to ventricular volume variations. These variations are used as triggers for changes in the heart's pumping speed. In real time, the volume increases during diastole (ventricular filling) and decreases during systole (ventricular ejection).

[0048] Thus, the transitions from diastolic velocity (low velocity during the ventricular filling phase) to systolic velocity (high velocity during ventricular ejection) can be driven by variations in impedance.

[0049] For example, a low impedance value may correspond to a filled ventricle and impending ejection. A high impedance value may correspond to an empty ventricle and impending refilling.

[0050] The heart pump operates at maximum programmed speed when the aortic valve opens if we consider the left ventricle or the pulmonary valve if we consider the right ventricle, and at minimum speed when the left / right ventricle fills with blood (diastole phase).

[0051] This automatically regulates the motor rate of the cardiac pump according to the natural and spontaneous timing of the implanted patient's heart.

[0052] The invention also allows for the definition of minimum and maximum values, or average values, for the impedance and / or volume of the heart. Monitoring these values ​​enables automatic management of the optimal pump ejection velocity, particularly in the event of these values ​​being exceeded.

[0053] According to an advantageous feature of the invention, all or part of the control parameters can be obtained from times t1, t2, t3 and t4.

[0054] According to one embodiment of the invention, the processing unit can be configured to determine, for example in real time or regularly, a stroke volume, a global ventricular volume, or a cardiac contractility index by calculating a ratio or difference between the maximum and minimum values ​​of the impedance variation for a cardiac cycle (diastole + systole).

[0055] The volume of the left ventricle is determined if the dipole is fixed to the myocardium of the left ventricle, or of the right ventricle if the dipole is fixed to the myocardium of the right ventricle.

[0056] Cardiac contractility is a parameter used to assess the effectiveness not only of the pump but also of the hemodynamic and clinical status of the implanted patient. Monitoring this relative value, which is proportional to the absolute value of cardiac contractility (the difference between the maximum diastolic volume of the ventricle and its minimum volume at the end of systole, i.e., at the end of contraction), over time allows for tracking the evolution of the patient's hemodynamic status.

[0057] Such a device allows for the monitoring of physiological parameters and the tracking of the progression of any potential heart failure.

[0058] According to the invention, the metallic part can be a component of the heart pump intended to be positioned either inside or outside the heart. This metallic part can also be the heart pump housing.

[0059] According to one embodiment of the invention, the processing unit can be configured to detect a cardiographic impedance in response to the detection of a QRS complex from an electrocardiogram.

[0060] In other words, a signal from an electrocardiogram is monitored to detect QRS complexes. If detected, a cardiographic impedance measurement procedure is initiated.

[0061] According to another aspect of the invention, a method for controlling a heart pump is proposed, comprising the following steps: a) the measurement of cardiographic impedance using a system as described above, b) the variation of cardiographic impedance during a cardiac cycle (systole + diastole) from the relative variation of ventricular volumes, c) the determination of pump control parameters, and d) the use of the control parameters to drive a cardiac pump motor.

[0062] With the method according to the invention, the cardiac pump is controlled according to the ventricular volume, the latter being obtained by cardiographic impedance measurement.

[0063] As mentioned above, determining pump control parameters may involve determining the following times: an instant t1 corresponding to the beginning of a ventricular depolarization of a cardiac activity cycle, the instant t1 being obtained from a local electrogram of ventricular activation, an instant t2 corresponding to the opening of the aortic valve, the instant t2 being obtained by impedance measurement by identifying the minimum impedance value or the beginning of the positivity of the derivative of the impedance with respect to time, an instant t3 corresponding to aortic closure, the instant t3 being obtained by impedance measurement by identifying a maximum in an impedance variation curve or by deduction from an instant t4, the instant t4 corresponding to the beginning of ventricular filling,The time t4 is obtained by impedance measurement, identifying the beginning of the negative change in the derivative of the impedance with respect to time.

[0064] According to the invention, the execution of steps a) to d) can be conditioned on the detection of a QRS complex by a local ventricular signal from an electrogram.

[0065] Steps a) to c) can be performed over at least one cardiac cycle before step d). Preferably, several values ​​for the control parameters are determined over the first few cardiac cycles, the values ​​obtained can be averaged, and then these parameters are applied to the heart pump over a predetermined duration or number of cardiac cycles. The control parameters are then determined again before being applied over a predetermined duration or number of cardiac cycles, and so on.

[0066] Other advantages and features of the invention will become apparent upon examination of the detailed description of a non-limiting embodiment and the accompanying drawings, in which: [ Fig.1 ] There [ Fig.1 ] is a schematic view of a cardiac pump implanted in a ventricle of a patient's heart, [ Fig.2 ] There [ Fig.2 ] illustrates representative graphs of the estimated ventricle volume, an electrocardiogram, and a signal from the heart pump motor, [ Fig.3 ] There [ Fig.3 ] is an electronic diagram of a bipolar configuration for cardiographic impedance measurement according to the invention, [ Fig.4 ] There [ Fig.4 ] is a representation of an electrocardiogram displaying two cardiac cycles, [ Fig.5 ] There [ Fig.5 ] is a functional diagram illustrating different implementation steps for detecting signals representative of aortic valve opening after detection of a QRS complex, [ Fig.6 ] There [ Fig.6 ] is an electronic diagram of a three-pole configuration for cardiographic impedance measurement according to the invention, [ Fig.7 ] There [ Fig.7 ] is a representation of an electrocardiogram displaying five cardiac cycles as well as times defining a measurement window, [ Fig.8 ] There [ Fig.8 ] a functional diagram illustrating different implementation steps for detecting signals representative of aortic valve opening in a predefined window after detection of a QRS complex.

[0067] The embodiments described below are not exhaustive; in particular, variants of the invention may be implemented comprising only a selection of the features described below, isolated from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0068] In the figures, elements common to several figures retain the same reference.

[0069] On the [ Fig.1 ], we distinguish a heart 1 comprising a ventricle 2 inside which a cardiac pump 3 is partially inserted.

[0070] The cardiac pump 3 may be such as that described in document US10,744,244. Other types of cardiac pump may be used, such as pumps draining blood in bypass from the apex of the left or right ventricle to the aorta (ascending or descending), whether internalized, externalized, axial / centrifugal turbine, vibrating / moving membrane, volumetric or non-volumetric.

[0071] This pump includes a motor located outside the heart. However, this motor 4 can be fully or partially integrated into the heart or into ventricle 2.

[0072] This motor 4 is designed to drive a transmission shaft 5 carrying blades 6. The transmission shaft 5 and blades 6 assembly propels the blood contained in the ventricle 2 towards the aorta (not shown). To accomplish this, the heart pump 3 includes a metal casing 7 surrounding the transmission shaft 5 and blades 6 assembly; this casing has an inlet 8 and an outlet 9. During operation, the blood contained in the ventricle 2 enters through the inlet 8, passes through the casing, and then exits through the outlet 9.

[0073] Ideally, motor 4 operates in pulsed mode, i.e., periods of operation at high speed and periods of operation at low speed.

[0074] The invention aims to control the motor 4 so that the pulsed mode corresponds to the heart rhythm and takes into account the physiological characteristics of the heart.

[0075] The engine speed is controlled by a processing unit 10 which may or may not be installed.

[0076] According to the invention, the treatment unit 10 is connected to a first pair of electrodes comprising a first electrode 11 and a second electrode which is the chamber 7 of the heart pump. The treatment unit 10 is therefore connected, for example by a wired connection, to the electrode 11 and the chamber 7.

[0077] The box 7 serves as a reference or ground for any electrical signal applied by the processing unit 10 between the electrode 11 and the box 7.

[0078] According to the invention, the processing unit 10 is connected to a second pair of electrodes comprising a third electrode 12 and a fourth electrode which is also the chamber 7 of the heart pump. The second and fourth electrodes are therefore a single electrode, which is the chamber 7. The first and second pairs of electrodes share a common electrode, which is the chamber 7.

[0079] The treatment unit 10 is therefore connected, for example by wired connection, to the electrode 12 and to the box 7.

[0080] The box 7 also serves as a reference or ground for any electrical signal applied by the processing unit 10 between the electrode 12 and the box 7.

[0081] The connection between the processing unit 10 and the box 7 is a conductive wire 13.

[0082] Electrodes 11, 12, and 7 are used to perform cardiographic impedance measurements. These measurements are then used to control motor 4 so that blades 6 propel blood from ventricle 2 to the aorta according to the patient's heart rhythm and physiological capabilities.

[0083] On the [ Fig.2 three curves are represented, C1 representing the estimated ventricular volume which is proportional to the cardiographic impedance, C2 representing an electrocardiogram, and C3 representing the motor regime 4.

[0084] According to the invention, two curves C1 and C2 are considered. C1 is obtained by cardiographic impedance measurement and C2 is obtained from, for example, a pacemaker probe not shown.

[0085] Curve C3 is obtained by deduction from the two curves C1 and C2.

[0086] To do this, time t1 is identified as the time of the R wave of a QRS complex on the electrocardiogram (ECG). Time t1 corresponds to the beginning of a ventricular depolarization of a cardiac activity cycle.

[0087] Time t2 is identified as a growth beyond a predetermined threshold on curve C1 (the moment when the derivative of the curve switches from positive to negative). Time t2 corresponds to the opening of the aortic valve for the left ventricle and the pulmonary valve for the right ventricle.

[0088] Time t4 is identified as a growth beyond a predetermined threshold on curve C1 (the moment when the derivative reverses from positive to negative because the ventricle fills with blood, the beginning of diastole). Time t4 corresponds to the beginning of diastolic filling.

[0089] Time t3 is determined by subtracting a predetermined value from time t4, or when the impedance curve reaches a minimum plateau value corresponding to the beginning of the isovolumic relaxation phase. Time t3 corresponds exactly to the closure of the aortic valve (for the left ventricle) or the pulmonary valve (for the right ventricle).

[0090] The average, minimum and / or maximum volume values ​​(C1 curve) are used to estimate the amount of blood to be ejected, and therefore the speed or power of motor 4. On curve C3, the heart pump motor operates between two regimes, a low diastolic speed at 2000 rpm and a high systolic speed at 6000 rpm.

[0091] The duration between t1 and t2 corresponds to the time it takes for the heart pump to rise between the low and high regimes.

[0092] The duration between t2 and t3 corresponds to the ejection time (systole).

[0093] The duration between t3 and t4 corresponds to the descent time from the high regime to the low regime.

[0094] The duration between t4 and t1 corresponds to the diastolic duration.

[0095] There [ Fig.3 ] illustrates an electronic impedance measurement circuit in a first configuration called bipolar. In this configuration, only one pair of electrodes is used. We distinguish the electrode pair 11 and 7 as represented on the [ Fig.1 ]. Between the two electrodes is biological tissue 14 corresponding to the wall of the heart and part of the blood in the ventricle 2.

[0096] The electrode 11 is supplied by a constant current Itx generated by a current generator 15. The latter can be integrated into the processing unit 10 or arranged independently.

[0097] A detector 16, integrated into the processing unit 10, measures the voltage Vrx between electrodes 11 and 7. This detector 16 includes an amplifier K and an analog-to-digital converter (ADC). The processing unit 10 is equipped with software and hardware for processing the digital signals from the ADC.

[0098] A microprocessor µp of the processing unit then processes the digital signal in order to calculate the cardiographic tissue impedance Z as a function of time t using the following formula: Z tissu t = Vrx t / Itx

[0099] The C1 curve corresponds to the different values ​​of Ztissu(t) or directly Vrx(t) over time. A multiplicative coefficient can be applied between the C1 curve and the Ztissu(t) or Vrx(t) values. Digital filters can be applied by the microprocessor µp to the detected signal to obtain a readily usable C1 curve.

[0100] The invention provides for recording variations in heart impedance continuously or at certain specific phases of the cardiac cycle as shown in the [ Fig.4 To do this, a single time zone is defined between the detected QRS complex and the end of the U wave of the surface electrocardiogram in which the Cardio Impedance (CI) is measured.

[0101] Thus, as shown on the [ Fig.5 In step 17, the electrocardiogram is monitored; each time a QRS complex is detected in step 18, an impedance measurement process 19 is triggered. This process includes: - Step 20 involves injecting an Itx current, - Step 21 involves acquiring and storing a Vrx voltage, - Step 22 involves verifying whether the aortic valve is open. To do this, the cardiographic impedance is calculated and compared to a previous value. - If the aortic valve is not open, step 23 checks whether the duration of the first time zone has elapsed. If so, the impedance measurement process 19 ends, and the process returns to step 17, corresponding to the second ECG monitoring time zone. If not, the impedance measurement process is restarted, returning to step 20, the current injection. - If the aortic valve is open, the impedance measurement process 19 ends, and the process returns to step 17, corresponding to the second ECG monitoring time zone.

[0102] In all embodiments, the opening of the aortic valve corresponds to detecting time t2. Starting from t1, as long as time t2 has not been detected, the aortic valve is considered not yet open.

[0103] There [ Fig.6 [ ] illustrates an electronic impedance measurement circuit in a second configuration known as tripolar. In this configuration, both pairs of electrodes are used, the first pair as the transmitting dipole, and the second pair as the receiving dipole. Electrode pair 11 and 7 are used as the transmitting dipole on the one hand, and electrode pair 12 and 7 as the receiving dipole on the other.

[0104] The invention provides a voltage generator 24 capable of generating a voltage Vtx across the terminals of the first pair of electrodes. This voltage Vtx is variable over time; it can be a square wave signal or any other signal at a predefined frequency f0.

[0105] The invention provides for a detector 25, in particular integrated into the processing unit 10, for detecting a voltage Vrx due to the propagation of an electric field created by the voltage Vtx through the biological tissue. This electric field can be represented by an amplitude Av.

[0106] Detector 25 includes an amplifier K, notably equipped with one or more analog filters, connected to electrodes 12 and 7.

[0107] The signal from amplifier K can be clipped using an envelope detector 26. The clipped signal is then converted into a digital signal by the analog-to-digital converter (ADC). A microprocessor µp in the processing unit then processes the digital signal to calculate the cardiographic impedance using the formula: Vrx t = Vtx t * cos 2 πf 0 t * Av t

[0108] The invention provides, as shown in the [ Fig.7 ], another impedance measurement process that takes place at predetermined times with detection of the precise moment of aortic valve opening. This precise detection allows monitoring of the lag between the heart's electrical activation and the valve opening.

[0109] To do this, a time zone is defined between the time T EGM and the time IC, the time interval between T EGM and IC being predefined and fixed. Within this time interval, a cardiographic impedance measurement is planned.

[0110] Thus, as shown on the [ Fig.8 In step 27, the electrogram (EGM) is monitored; each time a ventricular EGM is detected in step 28, a timer is triggered in step 29 and the impedance measurement process is initiated in step 30. This process includes: Step 31 involves applying a voltage Vtx, step 32 involves acquiring and storing a voltage Vrx, and step 33 involves verifying whether the aortic valve is open. To do this, the cardiographic impedance is calculated and compared to a previous value. If aortic valve opening has not been detected, step 34 checks whether the duration of the first time zone has elapsed. If so, a detection failure alert signal is generated in step 35, and the process returns to step 27, corresponding to the second ECG monitoring time zone. If not, the impedance measurement process is restarted by returning to step 32 for acquiring a voltage Vrx. If detection of aortic valve opening has occurred, the timer value is recorded in step 36 and then we return to step 27 corresponding to the second time zone of ECG monitoring.

[0111] The timer value thus obtained is to be compared to one or more previous values ​​to estimate any possible physiological degradation.

[0112] Of course, the invention is not limited to the examples just described.

Claims

1. Cardio-impedance measurement system comprising: - at least one first pair of electrodes having a first electrode (11) and a second electrode (7); the first electrode (11) being connected to a generator (15, 24) configured to generate an excitation signal, - said generator (15, 24), - a detector (16, 25) for detecting a voltage resulting from the propagation of the electric field created by the excitation signal, - a processing unit (10) configured to determine cardio-impedance from the detected voltage, characterized in that it further comprises an implantable cardiac pump (3) configured to be arranged wholly or partially within a ventricle; the second electrode (7) consisting of a metal part of the cardiac pump (3), and in that for each pair of electrodes, the first electrode is configured to be positioned on the outer surface of a heart and the second electrode within a ventricle of the heart.

2. System according to claim 1, characterized in that the generator is a current generator (15), and the detector is a voltage detector (16) connected between the first electrode (11) and the second electrode (7).

3. System according to claim 1, characterized in that it further comprises a second pair of electrodes having a third electrode (12) and a fourth electrode (7); the fourth electrode being the same as the second electrode used as a reference electrode; and in that the generator is a current generator (15) and the detector is a voltage detector connected between the third electrode and the second electrode.

4. System according to claim 1, characterized in that it further comprises a second pair of electrodes having a third electrode (12) and a fourth electrode (7); the fourth electrode consisting of said metal part of the cardiac pump (3); and in that the generator is a voltage generator (24) connected to the first pair of electrodes and the detector is a voltage detector (25) connected to the second pair of electrodes.

5. System according to any of the preceding claims, characterized in that the processing unit (10) is configured to determine a change in the volume of the heart.

6. System according to any of the preceding claims, characterized in that the processing unit (10) is configured to determine a movement of a wall of the heart.

7. System according to any of the preceding claims, characterized in that, for at least one cycle of a cardiac activity, the processing unit is configured to determine: - a time t1 corresponding to the onset of ventricular depolarization in a cycle of the cardiac activity, time t1 being obtained from a local ventricular activation electrogram - a time t2 corresponding to the opening of the aortic valve, time t2 being obtained by measuring impedance by identifying the minimum impedance value or the onset of the positive slope of the derivative of impedance with respect to time, - a time t3 corresponding to aortic closure, time t3 being obtained by measuring impedance by identifying a maximum in an impedance variation curve or by deducing it from a time t4, - a time t4 corresponding to the onset of ventricular filling, time t4 being obtained by measuring impedance by identifying the onset of the negative slope of the derivative of impedance with respect to time.

8. System according to claim 7, characterized in that it comprises a bipolar epicardial probe for generating the electrogram.

9. System according to any of the preceding claims, characterized in that the processing unit (10) is configured to determine control parameters of the cardiac pump (3).

10. System according to any of the preceding claims, characterized in that the processing unit (10) is configured to modulate operating cycles of a motor (4) of the cardiac pump on the basis of changes in the volume or movement of the wall of the heart, each cycle comprising at least a low pump speed and a high pump speed.

11. System according to claim 10, characterized in that the processing unit (10) is configured to modulate at least one of the following control parameters: - the time it takes to switch from the low speed of the pump to the high speed of the pump, - the time it takes to switch from the high speed of the pump to the low speed of the pump, - the duration for which the pump maintains its high speed, - the duration for which the pump maintains its low speed, - the value of the high speed of the pump, - the value of the low speed of the pump, corresponding to a diastolic speed.

12. System according to claim 7 and 11, characterized in that all or part of the control parameters are obtained from the times t1, t2, t3, and t4.

13. System according to any of the preceding claims, characterized in that the processing unit (10) is configured to determine a stroke volume, a total ventricular volume, or a cardiac contractility index by calculating a ratio or a difference between the maximum and minimum values of the impedance variation over a cardiac cycle.

14. System according to any of the preceding claims, characterized in that said metal part is the housing of the cardiac pump (3).

15. System according to any of the preceding claims, characterized in that the processing unit (10) is configured to detect a cardiographic impedance in response to the detection of a QRS complex in an electrocardiogram.