MODULE FOR CALCULATING A REGULATORY CARDIAC RHYTHM SEQUENCE FOR AN IMPLANTABLE PACEMAKER CONTROLLED TO A PATIENT'S ACTIVITY

Description

CONTEXT OF THE INVENTION Domaine de l'invention

[0001] The invention relates to implanted medical devices, in particular pacemakers that continuously monitor the patient's rhythm and deliver electrical stimulation impulses to the heart as needed to compensate for a myocardial sinus rhythm disturbance. The invention is particularly advantageously applicable—but not limitingly so—to leadless, capsule-type, self-contained implantable devices, which are implants devoid of any physical connection ( lead ) to a remote device.

[0002] The capsule includes various electronic circuits, sensors, etc., as well as wireless communication transmitter / receiver means for remote data exchange, all integrated into a very small body that can be implanted in hard-to-reach or space-constrained locations, such as the ventricle apex or the inner wall of the atrium.

[0003] One of the critical aspects of these miniaturized devices is that of electrical autonomy, and consequently that of the consumption of electronic circuits, which must be as low as possible.

[0004] With a leadless implant, given its extremely small size, it is not possible to use a conventional battery, even a high-density one. Therefore, a self-powering system is designed, featuring a harvester-type energy harvester that collects the mechanical energy resulting from the various movements of the implant body in rhythm with the heartbeat. This mechanical energy is then converted into electrical energy using a suitable transducer, thus recharging an integrated battery and powering the device's various circuits and sensors. This power system allows the device to operate completely independently throughout its lifespan, approximately 8 to 10 years.

[0005] WO 2019 / 001829 A1 (Cairdac) describes an example of such a self-contained intracardiac leadless capsule equipped with an integrated energy harvester.

[0006] The invention is not limited to this particular type of implant; it is also applicable to other types of battery-powered pacemakers whose lifespan must be preserved by minimizing the overall electrical consumption of the device.

[0007] Regarding stimulation, it is generally performed in VVIR or "rate-responsive" mode. This means that, in the case of a paced rhythm rather than a spontaneous (sinus) rhythm, the frequency of the stimulation pulses must be modulated according to the patient's physical activity, with a lower frequency when the patient is inactive and a higher frequency for increased physical activity. The frequency of the paced rhythm thus regulated will vary between a minimum frequency called the "baseline rate" (HR min) and the maximum rate (HR max) specific to the patient, which defines a ceiling for the stimulation frequency calculated by the rate-responsive algorithms.

[0008] Furthermore, the pacemaker's rate control should be as physiological as possible, replicating the sinus rhythm of a healthy heart with (i) a rapid increase in rate in the event of a sudden increase in activity (the patient standing up and walking, climbing stairs, etc.), and (ii) subsequently a very gradual and slow return to the baseline rate, on the order of several tens of seconds or several minutes after the detection of reduced activity (the patient who has finished climbing stairs but still needs to recover from the exertion, etc.). The rate of change of the pacemaker's rate, that is, the shape (linear or non-linear) of the rate / exercise characteristic, can also be adapted to the patient's physical activity.

[0009] To perform this servo function, the patient's instantaneous physical activity level is typically measured by a sensor called an "activity sensor" or "G sensor," which is typically an accelerometer, most often a 3D accelerometer.

[0010] This type of sensor, which delivers an accelerometric signal with very rapid and very high amplitude variations, is to be distinguished from "physiological sensor" or "exercise sensor" type sensors such as minute ventilation sensors or "MV sensors", which deliver a slowly varying signal representative of the patient's metabolic needs, and which are not applicable to the case of an autonomous leadless capsule (they are based on the measurement of a transthoracic impedance between the end of an intracardiac probe and a remote unit of a pacemaker generator). Description de la technique antérieure

[0011] The problem of the invention is that of the continuous (cycle-to-cycle) calculation of the optimal frequency of the stimulation pulses that the device must deliver, this frequency ideally being calculated at each cardiac cycle in order to optimize its adaptation to the patient's activity.

[0012] US 2020 / 0147396 A1 (Shelton et al. / Medtronic) describes a leadless pacemaker equipped with an accelerometer sensor that detects patient movement and activity level. The signal from the accelerometer sensor is sampled and filtered appropriately, then processed to determine a target rate for device control at each new cardiac cycle.

[0013] To reduce the power consumption of the integrated microprocessor that performs these operations, it is only made active during a limited sampling period, after the expiration of a blanking period during which sampling is suspended.

[0014] However, this solution is not optimal. Indeed: At each cardiac cycle, the awakening of the processor from sleep mode to active mode is not immediate: it requires several dozen processor cycles, i.e. a few microseconds to a few milliseconds, before it can begin to recalculate the stimulation rate; during this awakening phase, the processor's consumption is at least equivalent to its consumption during the active phase, even though it is not yet able to sample and process the signal; the algorithm is based on a cumulative total of 1000 previous values ​​of the stimulation rate (i.e., a duration of approximately 15 minutes) to take into account hysteresis, i.e., the fact that the law of variation is not the same in a situation of increased patient activity (requiring a rapid acceleration of the simulation rate) and in the case of a decrease in this activity (requiring a very gradual and slow return to the base rate).This long-term retrospective analysis requires approximately 2000 processor cycles before the control can be stabilized, resulting in an almost doubling of the power consumption of a servo algorithm (VVIR) compared to a simple, non-servo algorithm (VVI); finally, the presence of a blanking period means that part of the accelerometer signal remains masked and will never be taken into account for the servo calculation, thus reducing the accuracy of the latter.

[0015] The aim of the invention is to overcome these disadvantages and limitations by proposing a technique for continuous adaptation of the heart rate, advantageously applicable to a leadless implant, imposing only very low consumption of the internal circuits of the device, without degrading the performance of the control compared to known techniques. SUMMARY OF THE INVENTION

[0016] To solve the various problems and achieve the goals set out above, the invention essentially proposes a heart rate value calculation module comprising, in a manner known in itself, a heart rate setpoint value calculation module, HR, or heart rate interval, RR, intended to link the frequency of stimulation pulses delivered by an active implantable medical device to the activity of a patient, in which the setpoint HR or RR value is determined continuously by digital processing of a sampled activity signal representative of the instantaneous activity of the patient.

[0017] Characteristically, this module further comprises: a conversion stage, receiving as input a current value of the sampled activity signal and delivering as output a first target HR or RR value obtained by applying a predetermined activity / heart rate or activity / heart rate interval function to a current value of the sampled activity signal; a first low-pass digital filtering stage, comprising a recursive filter capable of calculating, over a first predetermined duration, a first moving average of the first target HR or RR value delivered by the conversion stage, giving as output a second target HR or RR value;and a combiner stage, receiving as input (i) the first target HR or RR value delivered by the conversion stage, and (ii) the second target HR or RR value delivered by the first low-pass digital filtering stage, and capable of determining the maximum of the two target HR values, or respectively the minimum of the two target RR values, received as input, giving as output the setpoint HR or RR value, to control the stimulation frequency according to the patient's activity. ;

[0018] According to various advantageous subsidiary characteristics: the module is integrated into an ASIC circuit; the module includes a microcontroller operating without sleep mode between two consecutive cardiac cycles; the module further includes a second stage of low-pass digital filtering, comprising a recursive filter capable of calculating, over a second predetermined duration shorter than the first predetermined duration, a second moving average of the first target HR or RR value, delivered by the conversion stage, so as to eliminate parasitic high-frequency noise components not representative of the patient's instantaneous activity, the combiner stage and the first stage of low-pass digital filtering receiving as input the first target HR or RR value, after it has been filtered by the second stage of low-pass digital filtering; the predetermined activity / heart rate function, or respectively the activity / heart interval function, is a linear function;To determine the patient's recovery time after a period of intense activity, the first predetermined duration for calculating the first moving average by the first stage of digital low-pass filtering is between 120 and 600 seconds; in the latter case, to determine the responsiveness of the adaptation of the heart rate or heart rate interval while eliminating very short-duration activity noise, the second predetermined duration for calculating the first moving average by the second stage of digital low-pass filtering is between 1 and 2 seconds; the recursive filter of the first and / or second stage of digital low-pass filtering is a first-order exponential recursive filter;and / or the recursive filter of the first and / or second low-pass filtering stage is a filter capable of calculating a moving average without numerical division or multiplication, in particular a filter capable of operating by bit shifting the numerical representation of the target HR or RR value at the input of the filtering stage. ;

[0019] The invention also relates to an active medical device of the type of an implantable autonomous capsule housing, within a device body, an electronic assembly comprising: a stimulation circuit, capable of delivering stimulation pulses; a circuit capable of delivering a signal representative of the instantaneous activity of a patient wearing the device; a module for sampling and extracting an activity signal sampled from the signal representative of the instantaneous activity of the patient; and a module for calculating a setpoint HR or RR value such as above, to control the frequency of the pulses delivered by the stimulation circuit according to the patient's activity. SUMMARY DESCRIPTION OF THE DRAWINGS

[0020] We will now describe an example of an embodiment of the present invention with reference to the attached drawings, where the same references designate identical or functionally similar elements from one figure to another. There Figure 1 illustrates a leadless capsule-type medical device in its environment, implanted at the bottom of a patient's right ventricle. Figure 2 This schematically presents the main functional blocks that make up the leadless capsule. Figures 3a et 3b illustrate how to regulate the patient's heart rate in the most physiological way possible, comparable to the natural adaptation in a healthy patient. Figure 4 is a schematic representation, in block form, of the different digital signal processing stages of a module according to the invention, enabling the delivery, from a sampled activity signal from an accelerometer, of a heart rate setpoint value suitable for application to the input of a servo stage of the stimulation circuit of an implanted device. Figures 5a à 5d are timing diagrams illustrating the values ​​of the sampled signals recorded at different levels of the module according to the illustrated invention Figure 4 , when variations in patient activity are detected. The Figure 6 is a characteristic of heart rate vs. activity level, corresponding to the activity variations illustrated in Figures 5a à 5d . DETAILED DESCRIPTION OF IMPLEMENTATION METHODS PREFERENTIALS OF THE INVENTION

[0021] We will now describe an example of an embodiment of the device of the invention, in an application to an autonomous implantable capsule intended to be implanted in a cardiac cavity.

[0022] As indicated above, this particular application is given only as an example of an embodiment and is not limiting to the invention, the lessons of which can be applied to many other types of autonomous devices incorporating or not a PEH type energy harvester.

[0023] On the Figure 1 , we have represented a leadless capsule type device 10 in an application to cardiac stimulation.

[0024] The capsule 10 has an external form resembling an implant, with an elongated cylindrical tubular body 12 enclosing the various electronic and power supply circuits of the capsule, as well as a pendulum-type energy harvester. Typical dimensions of such a capsule are a diameter of approximately 6 mm and a length of approximately 25 to 40 mm.

[0025] The tubular body 12 has at its front (distal) end 14 a protruding anchoring element, for example a helical screw 16, to secure the capsule at the implantation site. Other anchoring systems are usable and do not in any way modify the implementation of the present invention. The opposite (proximal) end 18 of the capsule 10 is a free end, which is only provided with means (not shown) for temporary connection to a guide catheter or other implantation accessory used for the placement or explantation of the capsule, which is subsequently detached from the capsule.

[0026] In the illustrated example Figure 1 The leadless capsule 10 is an intracardiac implant placed within a cavity 20 of the myocardium 22, for example, at the apex of the right ventricle. Alternatively, still in a cardiac pacing application, the capsule can also be implanted on the interventricular septum or on an atrial wall, or be an epicardial capsule placed on an external region of the myocardium; these different implantation methods do not in any way modify the implementation of the present invention. To perform the sensing / pacing functions, an electrode (not shown) in contact with the cardiac tissue at the implantation site records cardiac depolarization potentials and / or applies pacing pulses. In certain embodiments, the function of this electrode can be performed by the anchoring screw 16, which is then an active, electrically conductive screw connected to the sensing / pacing circuit of the capsule.

[0027] The leadless capsule 10 is also equipped with an energy recovery module called "PEH", comprising an inertial pendulum assembly that oscillates inside the capsule in response to various external stresses to which the capsule is subjected. These stresses may result in particular from: movements of the wall to which the capsule is anchored, which are transmitted to the tubular body 12 by the anchoring screw 16; and / or variations in blood flow in the medium surrounding the capsule, which produce oscillations of the tubular body 12 in rhythm with the heartbeats; and / or various vibrations transmitted by cardiac tissues.

[0028] The pendulum assembly consists of a piezoelectric blade 24 fixed at one end, the opposite end of which is free and coupled to a movable inertial mass 26. The piezoelectric blade 24 is a flexible, elastically deformable blade which, together with the inertial mass 26, forms a mass-spring type pendulum system. Due to its inertia, the mass 26 subjects the blade 24 to a vibratory deformation on either side of a neutral or undeformed position corresponding to a stable rest position in the absence of any load.

[0029] There Figure 2 is a synoptic diagram of the various electrical and electronic circuits integrated into the leadless capsule, presented in the form of functional blocks.

[0030] Block 28 designates a circuit for detecting the cardiac depolarization wave, which is connected to a cathode electrode 30 in contact with the cardiac tissue and to an associated anode electrode 32, for example, an annular electrode formed on the tubular body of the capsule. The detection block 28 includes filters and means for analog and / or digital processing of the acquired signal. The processed signal is applied to the input of a microcomputer 34 associated with a memory 36. The electronic assembly also includes a pacing circuit 38 operating under the control of the microcomputer 34 to deliver, as needed, myocardial stimulation pulses to the electrode system 30, 32.

[0031] Furthermore, an energy recovery circuit or PEH 40 is planned, consisting of the pendulum assembly formed by the piezoelectric blade 24 and the inertial mass 26 described above with reference to the Figure 1 .

[0032] The piezoelectric blade 24, which acts as a mechano-electric transducer, converts the mechanical stresses it undergoes into electrical charges and produces a variable electrical signal V OUT(t). This signal is an alternating current oscillating at the free oscillation frequency of the blade 24 / mass 30 pendulum assembly and at the rate of successive myocardial beats to which the capsule is coupled. This variable electrical signal V OUT(t) is delivered to a power management circuit, or PMU 42, which rectifies and regulates the signal V OUT(t) to produce a stabilized DC voltage or current output used to power the various electronic circuits and to recharge an integrated battery 44.

[0033] The leadless capsule also integrates a 46-digit heart activity sensor such as a 1D accelerometer, or preferably a 3D accelerometer, of piezoelectric, piezoresistive or capacitive type MEMS.

[0034] The sensor 46 continuously delivers a composite signal containing (i) components representative of the instantaneous activity of the patient wearing the device and (ii) components representative of the acceleration, due to heartbeats, of the wall on which the capsule is implanted.

[0035] After sampling and processing, this accelerometric signal will be used to control the frequency of the stimulation pulses delivered by the stimulation circuit 38 (VVIR type control stimulation) to the patient's activity, and / or to perform a capture test, i.e. detect the presence or absence of a myocardial contraction following the application of a stimulation pulse.

[0036] On the Figures 3a et 3b We illustrated how to control the patient's heart rate activity in the most physiological way possible, in a manner comparable to the natural adaptation in a healthy patient.

[0037] There Figure 3a is a chronogram showing, at the top, an example of the variation over time of a patient's activity, this activity being represented by an indicator in arbitrary units ranging from 0 to 5. At the bottom, the Figure 3a This illustrates how the heart in a healthy patient adapts to sudden changes in activity, specifically the fact that the response to the onset of activity differs from the response to the cessation of activity. For example, starting from a resting state A at 60 bpm (minimum resting heart rate HRmin), a sudden increase in activity B causes a very rapid increase in heart rate, in this example from 60 to 120 bpm (120 bpm being the patient's maximum heart rate HRmax in this example), with a response time of approximately 2 to 10 seconds. During sustained activity, in C, the heart rate remains elevated, in this example at the maximum heart rate HRmax. When activity suddenly decreases, in D, the heart rate declines steadily and gradually until it returns to the minimum heart rate HRmin, in E, with a response time of approximately 3 to 10 minutes.

[0038] This hysteresis of the response is visible in particular on the parametric diagram of activity vs. heart rate of the Figure 3b , corresponding to the values ​​given as an example in the Figure 3a .

[0039] There Figure 4 is a schematic representation, in block form, of the different digital signal processing stages of a module according to the invention, intended to deliver a heart rate setpoint value suitable for application as input to a control stage of a stimulation circuit of an implanted device.

[0040] The module 100 according to the invention receives as input a sampled activity signal ACT k. This sampled activity signal comes from a detection and digitization module which is not part of the present invention, and which may be of a type known in itself, not requiring any particular adaptation for the implementation of the present invention.

[0041] Since a patient's activity level is a parameter that varies in a relatively low frequency range, on the order of 1 to 7 Hz, the sampling rate can be relatively low, on the order of 4 Hz, i.e. 4 samples per second, or less.

[0042] Digitizing the activity signal yields a metric that is quantified by a limited number of integer values, for example a metric on 4 levels or 12 elementary levels.

[0043] At time t = k, the sample ACT k of the activity signal is applied to the input of a conversion stage 110 which applies to the current value ACT k a predetermined activity / heart rate function F(ACT) and delivers at the output a first target heart rate value X k.

[0044] The target heart rate must necessarily be between the minimum value HR min (baseline rate) and a maximum value HR max; in the case of a linear activity / heart rate function, the function F is of the form: X k = MAX HR min , MIN a . ACT k + b . HR max .

[0045] The values ​​of the slope a and the y-intercept b are specific to each patient, and can be parameters configurable by the doctor at the time of implantation or during a follow-up visit.

[0046] Alternatively, the function F can be a nonlinear, monotonic function (as in the example of the curve arc AC of the Figure 3b corresponding to the natural response of a heart in a healthy patient), or defined by successive segments, possibly configurable by the doctor, for example by means of a graphical interface on a tablet at the time of implantation or a check-up visit.

[0047] The heart rate / activity function F of conversion stage 110 defines an initial target heart rate value Xk, but does not define the time interval required to reach this initial target value Xk. As mentioned above, to replicate the heart response of a healthy patient, it is desirable to: (i) that the heart rate increases immediately after the start of the activity. A typical example is a patient who is seated, then stands up and starts climbing stairs: it is essential that the heart rate increases very rapidly in such a case. The response time to reach the target heart rate will typically be on the order of 2 to 10 seconds, depending on the patient's lifestyle (for a patient with an active lifestyle, the response time should be much shorter than for a sedentary one); (ii) that the heart rate decreases slowly and steadily after the activity stops, with a typical time constant on the order of 2 to 10 minutes; and (iii) to ensure immunity to insignificant noise detected by the accelerometer of the activity detection circuit.In particular, signals in a high frequency range, or sudden but transient changes in activity level, should not lead to a rapid change in heart rate. For example, in the case of a patient who turns over in bed, or who coughs, their heart rate should not be altered, or not significantly altered, even though these episodes will produce a sudden, but brief, variation in activity detected by the accelerometer.

[0048] To meet these various requirements, the target heart rate value X k will undergo specific filtering processing, detailed below, operated by stages 120 to 140.

[0049] Stage 120 is a low-pass digital filtering stage H1 designed to eliminate the high-frequency noise mentioned above. Advantageously, the H1 filter is a first-order recursive exponential filter, calculating the average of the values ​​Xk over a duration τ1 on the order of 1 or 2 seconds, depending on the activity detection sampling rate. In a simple implementation, and therefore economical in terms of circuit power consumption, the recursive equation of the H1 filter can be performed without division or multiplication, for example, by dividing the signal by 8: indeed, such a division corresponds to a simple one-bit left shift of the digital value of the signal Xk.

[0050] More specifically, the output of the recursive filter H1 is of the form: Y k = 1 − α 1 . Y k − 1 + α 1 . X k ,

[0051] Y k being the current value of Y k and Y k-1 being the previous value in the sample sequence.

[0052] In a division by 8, with a sampling rate of 4 Hz (4 samples per second) and an average calculated over τ 1 = 2 s, the weighting (1 - α 1 ) will be 7 / 8 and that of α 1 will be 1 / 8.

[0053] When the next activity sample is acquired, updating the Y value with the new X value can be done in two operations: Y = M * Y − Y + X , And Y = Y / M , where M is an integer, rounded value of F s × τ 1 , F s being the activity detection sampling frequency and τ 1 being the predetermined constant, for example τ 1 = 1 or 2 s.

[0054] If we take M to be a power of 2 (M = 2^N), the calculation can be performed simply by the following bit manipulation: Y = Y ≪ N − Y + X , And Y = Y ≫ N , where Y << N represents the binary value of Y shifted left by N bits (which is equivalent to multiplying Y by M), and Y >> N represents the binary value of Y shifted right by N bits (which is equivalent to dividing Y by M).

[0055] The target value Yk delivered at the output of stage 12 is applied to a stage 130, which is a low-pass filtering stage H2 designed to take into account the hysteresis of the activity decay episodes. Advantageously, the H2 filter is a first-order recursive exponential filter, calculating a moving average of the input signal Yk, with a long time constant τ2, for example 120 s, 300 s or 600 s (value corresponding to the duration of the decay time when the activity ceases).

[0056] The output signal Zk of the H2 filter in stage 130 is given by: Z k = 1 − α 2 . Z k − 1 + α 2 . Y k .

[0057] Z represents the moving average of Y over a period τ 2, and can be calculated by simple bit shifts in the same way as described above for H1 filtering, without costly multiplications or divisions in terms of processor consumption.

[0058] Once these two filters H1 and H2 have been operated, we have at the output of stages 120 and 130 two filtered values, respectively Y k and Z k, which are applied simultaneously at the input of a stage 140.

[0059] Stage 140 is a combiner stage that delivers the higher of the two values ​​Yk and Zk at its output: HR k = MAX Y k , Z k .

[0060] HR k will be the final target value intended to serve as a setpoint for the control of the heart rate by the stimulation pulse delivery circuit.

[0061] The HR k value thus obtained is a smoothed and differentiated setpoint value depending on whether we are in a phase of increasing activity (in this case HR k = Y k) or decreasing activity (in this case HR k = Z k).

[0062] THE Figures 5a à 5d are chronograms illustrating values ​​of sampled signals taken at different levels of the module according to the invention described above, during detected variations in patient activity.

[0063] There Figure 5a shows an example of activity variation in a patient, with a sudden increase at t = 50 s, the activity ceasing at t = 250 s. We have also represented in P on this figure a peak of high value but very brief activity (corresponding to a jump, a cough, etc), therefore a spurious peak for which there is normally no need to modify the heart rate.

[0064] There Figure 5b illustrates the first target heart rate value X k at the output of stage 110 of activity vs. heart rate conversion, which therefore follows in conformity the variations of activity, including the spurious peak P.

[0065] There Figure 5c Figure 1 shows the corresponding variations of the first and second values ​​of the target signal, namely Yk at the output of the first low-pass filter stage H1 (dashed line) and Zk at the output of the second low-pass filter stage H2 (dashed line). As can be seen, the H1 filter significantly reduced the intensity of the spurious peak P while preserving the variation in the activity level.

[0066] There Figure 5d This shows the final setpoint value HR k at the output of the combiner stage 140: in A, in the absence of activity, the signal Z k is selected; when activity increases sharply in B, the signal Y k is selected, and this continues as long as the activity remains at a high level in C. When activity suddenly decreases, the value Z k is selected, with a much longer time constant, in D, thus allowing the simulation of the functioning of a heart in a healthy patient, in a manner comparable to what had been explained and illustrated. Figure 3a .

[0067] There Figure 6 illustrates the variations in the HR k setpoint value of the Figure 5d , in a parametric form: heart rate vs. activity level.

[0068] As can be seen, the peak activity (P) produces a significant variation on the curve, but this variation does not lead to a significant change in heart rate: in this example, the rate only increases by 60 to 70 bpm. In contrast, when activity is sustained at a high level (C), the heart rate rapidly increases to its maximum value (HR max), here 120 bpm.

[0069] The method of proceeding that has just been described, which is characteristic of the invention, has many advantages.

[0070] In particular, the impact of calculating the setpoint value on the energy consumption of the circuits is particularly low, especially if only integer values ​​are used for the calculation (i.e., without floating-point calculations). Furthermore, this calculation requires only a very limited number of memory cells, without the need to store a large amount of historical data for the activity signal or the heart rate signal.

[0071] Finally, it should be noted that, in a simplified version, it is possible to remove the first low-pass filtering stage 120, with in this case Y k = X k.

[0072] This allows for even simpler circuits, but with less immunity to parasitic noise from the activity signal collected by the accelerometer sensor.

[0073] Furthermore, in one embodiment of the invention, the calculation of target values ​​is not carried out in terms of heart rate (i.e. frequency), but in terms of cardiac interval (i.e. duration), the cardiac interval typically corresponding to the RR interval between two successive QRS complexes of a heartbeat.

[0074] The function F of the conversion stage 110 will then be a decreasing function and no longer an increasing one (the heart rate interval must decrease when the activity increases), and the combiner stage 140 will select the minimum (and no longer the maximum) of the heart rate interval values ​​filtered at the output of the low-pass stages 120 and 130.

Claims

1. A module for calculating a cardiac rhythm, HR, setpoint value (HRk), for controlling a rate of pacing pulses (38) issued by an active implantable medical device (10) based on a patient's activity, wherein the HR setpoint value (HRk) is continuously determined by digital processing of a sampled activity signal (ACTk) representative of a patient's instantaneous activity, characterized by comprising: - a conversion stage (110), receiving as an input a current value of the sampled activity signal (ACTk) and outputting a first target HR value (Xk), obtained by application of a predetermined activity vs. cardiac rhythm function (F(ACT)) to a current value of the sampled activity signal (ACTk); - a first low-pass digital filtering stage (130), comprising a recursive filter adapted to calculate, over a first predetermined duration, a first moving average of the first target HR value (Xk) issued by the conversion stage (110), thereby outputting a second target HR value (Zk); and - a combiner stage (140), receiving as an input (i) the first target HR value (Xk) issued by the conversion stage (110), and (ii) the second target HR value (Zk) issued by the first low-pass digital filtering stage (130), and adapted to determine a maximum of the first and second target HR values received as an input, thereby outputting the HR setpoint value (HRk) to control the rate of pacing pulses based on the patient's activity.

2. A module for calculating a cardiac interval, RR, setpoint value, for controlling a rate of pacing pulses (38) issued by an active implantable medical device (10) based on a patient's activity, wherein the RR setpoint value is continuously determined by digital processing of a sampled activity signal (ACTk) representative of the patient's instantaneous activity, characterized by comprising: - a conversion stage (110), receiving as an input a current value of the sampled activity signal (ACTk) and outputting a first target RR value, obtained by application of a predetermined activity vs. cardiac interval function (F(ACT)) to a current value of the sampled activity signal (ACTk); - a first low-pass digital filtering stage (130), comprising a recursive filter adapted to calculate, over a first predetermined duration, a first moving average of the first target RR value issued by the conversion stage (110), thereby outputting a second target RR value; and - a combiner stage (140), receiving as an input (i) the first target RR value issued by the conversion stage (110), and (ii) the second target RR value issued by the first low-pass digital filtering stage (130), and adapted to determine a minimum of the first and second target RR values received as an input, thereby outputting the RR setpoint value, to control the rate of pacing pulses based on the patient's activity.

3. The module of claim 1 or claim 2, wherein the module is integrated to an ASIC circuit.

4. The module of claim 1 or claim 2, wherein the module comprises a microcontroller operating without being put to sleep between two consecutive cardiac cycles.

5. The module of claim 1 or claim 2, wherein the module further comprises: - a second low-pass digital filtering stage (120), comprising a recursive filter adapted to calculate, over a second predetermined duration shorter than the first predetermined duration, a second moving average of the first target HR value (Xk), or respectively the first target RR value, issued by the conversion stage (110), thereby eliminating parasitic high-frequency noise components that are not representative of the patient's instantaneous activity, and wherein the combiner stage (140) and the first low-pass digital filtering stage (130) receive as an input the first target HR value (Xk), or respectively the first target RR value, after the latter has been filtered by the second low-pass digital filtering stage (120).

6. The module of claim 1 or claim 2, wherein the predetermined activity vs. cardiac rhythm function, or respectively the predetermined activity vs. cardiac interval function, (F(ACT)), is a linear function.

7. The module of claim 1 or claim 2, wherein, to determine the patient's recovery time after a period of intense activity, the first predetermined duration for the first low-pass digital filtering stage (130) to calculate the first moving average is between 120 and 600 seconds.

8. The module of claim 5, wherein, to determine the reactivity of the cardiac rhythm, or respectively of the cardiac interval, adaptation, while eliminating activity noises of very short duration, the second predetermined duration for the second low-pass digital filtering stage (120) to calculate the first moving average is between 1 and 2 seconds.

9. The module of claim 1, claim 2, or claim 5, wherein the recursive filter of at least one of the first low-pass digital filtering stage(130) and the second low-pass digital filtering stage (120) is an exponential recursive filter of the 1st order.

10. The module of claim 1, claim 2, or claim 5, wherein the recursive filter of the first low-pass digital filtering stage (130) and / or the second low-pass digital filtering stage (120) is a filter adapted to calculate a moving average without division nor multiplication.

11. The module of claim 10, wherein the recursive filter of the first low-pass digital filtering stage (130) and / or the second low-pass digital filtering stage (120) is a filter adapted to operate by shifting bits of the digital representation of the HR value, or respectively of the target RR value, at the input of the filtering stage.

12. An active medical device (10) of the implantable autonomous capsule type which houses, in a device body (12), an electronic unit including: - a pacing circuit (38), adapted to issue pacing pulses; - a circuit (46, 34) adapted to issue a signal representative of the instantaneous activity of a patient wearing the device; - a module for sampling or extracting a sampled activity signal (ACTk) from the signal representative of the patient's instantaneous activity; and - a module (110-140) according to any of claims 1 to 11 for computing a HR or RR setpoint value, to control a rate of the pacing pulses issued by the pacing circuit (38) based on the patient's activity.