Implantable medical stimulation device for performing a pacing in an atrium of a patient's heart

Abstract

The invention relates to an implantable medical stimulation device (1) for stimulating an atrium (RA) of a patient's heart (H), comprising a generator device (12) with a processing circuitry (120) configured to perform a rate-adaptive cardiac stimulation in which a paced heart rate is adjusted based on a load state of the patient. The processing circuitry (120) is further configured to obtain a momentary impedance curve (ΔZ1) indicative of a measured impedance during a cardiac cycle, to compare said momentary impedance curve (ΔZ1) to a stored reference curve (ΔZrefRest) indicative of a reference impedance curve and to perform an adaption of the paced heart rate based on the comparison of the momentary impedance curve (ΔZ1) to the stored reference curve (ΔZrefRest). The processing circuitry (120) is furthermore configured to obtain said momentary impedance curve (ΔZ1) using at least one ventricular electrode pole (102).

Description

[0001] Applicant: BIOTRONIK SE & Co. KG

[0002] Date: 02.10.2025

[0003] Our Reference: 23.182P-WO

[0004] Implantable medical stimulation device for performing a pacing in an atrium of a patient’s heart

[0005] The present invention relates to an implantable medical stimulation device for performing a stimulation of an atrium of a patient’s heart according to the preamble of claim 1 and to a method for operating an implantable medical stimulation device for performing a stimulation of an atrium of a patient’s heart.

[0006] An implantable medical stimulation device of this kind comprises a generator device comprising processing circuitry for processing cardiac sense signals and generating cardiac stimulation signals. In addition, the implantable medical stimulation device comprises an electrode arrangement for sensing cardiac signals and outputting cardiac stimulation signals. The electrode arrangement includes at least one atrial electrode pole which is configured to be placed in the atrium of the patient’s heart for sensing signals and outputting cardiac stimulation signals in the atrium of the patient’s heart. The electrode arrangement furthermore comprises at least one ventricular electrode pole which is configured to be placed in a ventricle of the patient’s heart for sensing signals in the ventricle of the patient’s heart.

[0007] An implantable medical stimulation device of the type concerned herein may for example be configured for subcutaneous implantation, such that the generator device during implantation is subcutaneously implanted in a patient. Herein, an electrode arrangement may be provided on one or multiple electrode leads extending from the generator device into the patient’s heart.

[0008] In another embodiment, the implantable medical stimulation device may be a leadless device not comprising any electrode leads, the leadless device being configured for immediate implantation into the patient’s heart. In this case, electrode poles of the electrode arrangement are arranged on the housing of the leadless device. Since the implantable medical stimulation device requires at least one atrial and at least one ventricular electrode pole, the leadless devices requires two separate housings, one of which is to be implanted into the atrium and the other one of which is to be implanted into the ventricle of the patient’ s heart.

[0009] During operation of the implantable medical stimulation device, the processing circuitry of the generator device generates and outputs, using the electrode arrangement, cardiac stimulation signals in order to provide for an atrial stimulation, such as an anti-bradycardia pacing, i.e., a pacing to increase a slower-than-normal heart rate to a regular heart rate, e.g. above 60 bpm.

[0010] Herein, the processing circuitry is configured to perform a rate-adaptive cardiac stimulation in which a paced heart rate is adjusted based on a load state of the patient. If it is, for example, found that the patient is physically active such that an increased heart rate is indicated, a paced heart rate may be adapted such that a pacing at an increased heart rate occurs.

[0011] In particular, for the rate-adaptive cardiac stimulation the processing circuitry is configured to obtain a momentary impedance curve indicative of a measured impedance during a cardiac cycle, to compare the momentary impedance curve to a stored reference curve indicative of a reference impedance curve in a defined state, e.g. a rest state, of the patient and to perform an adaption of the paced heart rate based on the comparison of the momentary impedance curve to the stored reference curve.

[0012] A rate-adaptive cardiac stimulation scheme is for example described in US 6,263,243 Bl. Within the rate-adaptive cardiac stimulation scheme a momentary impedance curve is measured and compared to a reference curve. Based on a deviation of the momentary impedance curve with respect to the reference curve the paced heart rate is adapted such that a pacing at an increased heart rate occurs, wherein the heart rate increase depends on the deviation of the momentary impedance curve from the reference curve. If for example only

[0013] 23.182P-WO | 02.10.2025 a slight deviation is detected, the heart rate is only slightly adapted. If, in contrast, a large deviation is detected, a large heart rate adaption takes place.

[0014] In a current rate-adaptive cardiac stimulation scheme, as for example described in US 6,263,243 B 1, a maximum heart rate may be programmed, beyond which the paced heart rate may not increase. If a large deviation of the momentary impedance curve with respect to the stored reference curve is identified, potentially the paced heart rate may be increased up to the programmed maximum heart rate, but not above the programmed maximum heart rate.

[0015] It is an object of the present invention to provide an implantable medical stimulation device and a method for operating an implantable medical stimulation device which allow for controlling operation for a rate-adaptive cardiac stimulation for a wider variety of operating modes of the implantable medical stimulation device, in particular for applications with an exclusive atrial stimulation.

[0016] This object is achieved with an implantable medical stimulation device comprising the features of claim 1.

[0017] Such an implantable medical stimulation device comprises the elements described above. In addition, the processing circuitry is configured to obtain said momentary impedance curve using the at least one ventricular electrode pole, in particular using only the at least one ventricular electrode pole.

[0018] When sensing electrocardiogram signals in the ventricle, in particular the right ventricle, ventricular electrocardiogram signal features, in particular the QRS complex relating to a depolarization of the ventricles of the patient’s heart during a cardiac cycle, may be predominantly measured and are generally strong, such that a momentary impedance curve may easily be synchronized to a ventricular electrocardiogram signal, in particular a QRS complex in a cardiac cycle. Briefly, the ventricular signals sensed with the at least one ventricular electrode pole have a better signal-to-noise ratio than ventricular signals sensed with the at least one atrial electrode pole.

[0019] 23.182P-WO | 02.10.2025 The implantable medical stimulation device is configured to provide for an atrial stimulation such as a defibrillation stimulation, a cardiac resynchronization stimulation (with or without defibrillation function), or an anti-bradycardia pacing. Thus, the implantable medical stimulation device can be, e.g., a cardiac pacemaker, an implantable cardiac defibrillator, an implantable cardiac resynchronization device, or an implantable cardioverter-defibrillator. For performing the stimulation, the processing circuitry is configured to carry out a rate- adaptive cardiac stimulation scheme. Within the rate-adaptive cardiac stimulation, a paced heart rate is adjusted based on a load state of the patient, such that with changing load of the patient the paced heart rate is adapted in order to adjust the heart rate to the actual load condition of the patient.

[0020] If for example a patient is physically active and hence is in a load state of increased physical load, the paced heart rate is adapted such that the heart rate is increased, hence adapting to the current load state of the patient. Likewise, if a patient is mentally active and hence is in a mental load state, the paced heart rate may be adapted accordingly and likewise may be increased. By performing a rate-adaptive cardiac stimulation, hence, a paced rate is not fixed, but is adaptively changed during operation of the implantable medical stimulation device in dependence of an actual load state of the patient.

[0021] For performing the rate-adaptive cardiac stimulation, a momentary impedance curve is compared to a stored reference curve. Based on a deviation of the momentary impedance curve to the stored reference curve the paced heart rate is set, wherein a large deviation of the momentary impedance curve to the stored reference curve causes a large adaption of the heart rate, whereas a slight deviation of the momentary impedance curve to the stored reference curve causes only a slight modification of the heart rate.

[0022] The processing circuitry hence stores a reference curve which is indicative of a reference impedance curve, in particular in a defined state of the patient, e.g. in a rest state of the patient. The reference curve may be determined and stored during a calibration phase and may be repeatedly adapted during operation of the implantable medical stimulation device. The stored reference curve hence provides for a reference of an impedance curve during a

[0023] 23.182P-WO | 02.10.2025 cardiac cycle in a defined state, for example a rest state, of the patient, such that based on a comparison of a momentary impedance curve to the stored reference curve a deviation from the defined state may be identified.

[0024] The implantable medical stimulation device for performing the anti-bradycardia pacing comprises an electrode arrangement including at least one atrial electrode pole configured to be placed in the atrium of the patient’s heart, in particular in the right atrium, for sensing electrocardiogram signals and for outputting cardiac stimulation signals in the atrium, in particular in the right atrium. The electrode arrangement furthermore comprises the at least one ventricular electrode pole configured to be placed in a ventricle, in particular the right ventricle of the patient’s heart for sensing electrocardiogram signals in the ventricle, in particular the right ventricle of the patient’s heart. By means of the electrode arrangement, signals may be sensed and stimulation signals may be output. The sensing takes place using the one or multiple ventricular electrode poles which, in an implanted state of the implantable medical stimulation device, rest within the ventricle, in particular the right ventricle, of the patient’s heart. In addition, sensing of atrial signals with the at least one atrial electrode pole is optionally also possible. The outputting of signals takes place using the one or multiple atrial electrode poles which, in an implanted state of the implantable medical stimulation device, rest within the atrium, in particular the right atrium, of the patient’s heart.

[0025] Using the electrode arrangement, also an impedance signal is recorded to obtain a momentary impedance curve indicative of a measured impedance during a cardiac cycle. In particular, using the at least one ventricular electrode pole impedance values may be repeatedly measured, such that by recording a multiplicity of measured impedance values during a cardiac cycle a momentary impedance curve associated with the cardiac cycle is obtained. The recording of the impedance signal is typically done in a unipolar manner, i.e., by recording a unipolar impedance curve. The single electrode pole is the at least one ventricular electrode pole. A housing of the implantable medical stimulation device serves as counter electrode pole.

[0026] Because the sensing of electrocardiogram signals and the outputting of cardiac stimulation signals as well as the measurement of the momentary impedance curve takes place by using

[0027] 23.182P-WO | 02.10.2025 the at least one ventricular electrode pole, a rate-adaptive cardiac stimulation scheme by putting a momentary impedance curve in relation to a reference curve may be employed, while sensing signals using the at least one ventricular electrode pole. It hence becomes possible to apply a rate-adaptive cardiac stimulation in a dual chamber pacemaker employing a stimulation only in one chamber, i.e., in the (right) atrium of the patient’s heart, and a sensing at least in the ventricle, but generally allowing also a sensing both in the ventricle and in the atrium. Thus, the implantable medical stimulation device can be operated in AVI mode, indicative of a mode in which a stimulation takes place in the atrium, a sensing takes place in the ventricle, and in addition an inhibition is applied which suppresses a stimulation pulse if an intrinsic atrial contraction is sensed at a normal cardiac interval (simply put, “inhibition” indicates that the stimulation device only comes into action when the heart rate falls below a defined frequency to perform an anti-bradycardia pacing). Likewise, the stimulation device can be operated in ADI mode, indicative of a mode in which a stimulation takes place in the atrium, a sensing takes place in the atrium and in the ventricle, and in addition an inhibition is applied.

[0028] As the momentary impedance curve shall be compared to a reference curve in order to perform an adaption of the paced heart rate, in particular of the paced atrial rate, based on the comparison of the momentary impedance curve to the stored reference curve, it is necessary to synchronize the momentary impedance curve to the reference curve such that a sensible comparison is enabled. For example, as the shape of the impedance curve is predominantly influenced by ventricular contraction activity, a measurement window for obtaining the momentary impedance curve as well as the window of the reference curve shall encompass ventricular activity, in particular the region of the QRS complex in the electrocardiogram signal, wherein the window of the momentary impedance curve and the window of the reference curve shall correspond to one another in order to enable a sensible comparison of the momentary impedance curve to the reference curve. In particular, synchronization of the momentary impedance curve to the reference curve may be implemented such that the momentary impedance curve is recorded only within the measurement window that, at least partly, corresponds to the window of the reference curve, or such that the momentary impedance curve is recorded over the full heart cycle and the corresponding windows are identified using a recorded electrocardiogram.

[0029] 23.182P-WO | 02.10.2025 In an embodiment, the processing circuitry is configured to synchronize the momentary impedance curve to the reference curve based on the occurrence of an atrial event. Such atrial event may be a sensing event sensed using the electrode arrangement and hence may be identified based on electrocardiogram signals. In other embodiments, such atrial event may relate to a pacing event. If the momentary impedance curve is synchronized with the help of an atrial event, recording the impedance curve can be started directly after an atrial sense event. Thus, in contrast to an impedance measurement in the presence of ventricular pacing, here, recording of an impedance curve does not need to be delayed until a ventricular blanking interval has passed to prevent an influence of a ventricular pacing pulse or a post potential to the impedance measurement. Even a better impedance signal is recorded which extend on the one hand over a longer time period and on the other hand covers the begin of a cardiac contraction. The begin of a cardiac contraction is a particular interesting signal section since the impedance curve behaves very dynamically and shows a higher gradient so that the momentary impedance curve can be better distinguished from the reference curve.

[0030] In an embodiment, the processing circuitry is configured to identify an atrial event based on an outputting of an atrial pace signal using the electrode arrangement. The atrial event hence is an atrial pacing event. As the implantable medical stimulation device shall provide for an atrial pacing, for example in an ADI mode, the output of an atrial pace signal provides for a defined event, according to which the momentary impedance curve as measured using the electrode arrangement may be synchronized to the reference curve. Also in this case, since no ventricular pacing is applied, it is not necessary to take into account a stimulation in the ventricle so that all of the properties and advantages explained in the preceding paragraph also apply to this embodiment. In case of a synchronization to an atrial pace, the recording of the momentary impedance curve typically begins after a time delay, the so-called crossblanking interval, has passed to avoid an undesired superposition of the atrial stimulation pulse and ventricular signals, i.e., a cross talk between the atrial stimulation pulse (or its post-potential) and a ventricular channel that is intended to sense “real” ventricular signals. Thus, the time delay serves for reducing the risk of sensing and recording atrial artefacts with the at least one ventricular electrode pole.

[0031] 23.182P-WO | 02.10.2025 In an embodiment, the processing circuitry is configured to identify an atrial event based on a sensing of an atrial electrocardiogram signal feature using the at least one atrial electrode pole of the electric arrangement. Using the at least one atrial electrode pole, hence, in an electrocardiogram signal a signal feature may be identified relating to atrial activity, such as the atrial P wave, which may be identified as an atrial event.

[0032] For example, the processing circuitry may be configured to synchronize the momentary impedance curve to the reference curve based on a defined delay time subsequent to the atrial event. By using a delay time subsequent to the paced or sensed atrial event, hence, a measurement window for the impedance curve may be defined, wherein the momentary impedance curve may be recorded throughout a measurement window which is configured such that it covers a time range in which typically a ventricular contraction event, or at least the begin of a ventricular contraction event, may be expected. Defining a measurement window exhibits the advantage that a momentary impedance curve can be recorded in a storage-space- and energy-saving manner.

[0033] The time delay or delay time may, for example, lie in a range from 10 ms to 40 ms, in particular from 20 ms to 30 ms, and marks the start of the window of the momentary impedance curve subsequent to the identified atrial event. The window of the momentary impedance curve may for example have a duration lying in a range from 300 ms to 700 ms, in particular from 300 ms to 550 ms, in particular from 350 ms to 500 ms, in particular from 400 ms to 450 ms.

[0034] In an embodiment, the processing circuitry is configured to identify an intrinsic ventricular event based on a sensing of a ventricular electrocardiogram signal feature using the at least one ventricular electrode pole of the electrode arrangement and to use the intrinsic ventricular event for synchronizing the momentary impedance curve to the reference curve. The ventricular event is, e.g., a QRS complex or the beginning of a QRS complex such as the Q wave or the ascending branch of the R wave.

[0035] In an embodiment, the processing circuitry is configured to synchronize the momentary impedance curve to the reference curve based on a comparison of the momentary impedance

[0036] 23.182P-WO | 02.10.2025 curve and the reference curve. For example, the processing circuitry may be configured to synchronize the momentary impedance curve to the reference curve by comparing an impedance signal feature of the momentary impedance curve to a corresponding impedance signal feature of the reference curve. For example, it may be observed when the momentary impedance curve and the reference curve cross and hence exhibit an equal impedance value, wherein the window of the momentary impedance curve may be started when the crossing occurs, i.e., the impedance value at the start of the momentary impedance curve is equal to the (predefined) impedance value at the start of the reference curve. The synchronization of the momentary impedance curve to the reference curve hence takes place based on the impedance measurement by conducting a feature analysis of the momentary impedance curve in relation to the reference curve, for example by observing when an initial crossing of the two curves occurs and by then synchronizing the momentary impedance curve to the reference curve based on the crossing.

[0037] The processing circuitry, in an embodiment, is configured for computing different measures for synchronizing the momentary impedance curve to the reference curve, for example based on atrial events and / or ventricular events and / or based on impedance features, wherein the processing circuitry may be configured for employing one or multiple synchronization methods for establishing a synchronicity of the momentary impedance curve as measured during a cardiac cycle and the stored reference curve.

[0038] In an embodiment, the generator device only enables an atrial stimulation but not a ventricular stimulation with the at least one ventricular electrode pole. Thus, in this embodiment, the at least one ventricular electrode pole serves exclusively for sensing cardiac signals but not for providing stimulation signals.

[0039] In an embodiment, the implantable medical stimulation device comprises an atrial electrode lead comprising the at least one atrial electrode pole, the electrode lead comprising a distal end configured for implantation in the atrium, in particular the right atrium, of the patient’s heart. The implantable medical stimulation device for example may comprise multiple electrode leads, wherein at least one electrode lead is to be implanted in the atrium of the patient’s heart and another electrode lead is to be implanted in the ventricle of the patient’s

[0040] 23.182P-WO | 02.10.2025 heart. Electrodes herein are placed on the one or the multiple leads, wherein a counterelectrode, for example serving as an anode, for sensing electrocardiogram signals as well as for measuring an impedance signal may be formed by the housing or a housing portion of the generator device.

[0041] A first atrial electrode pole may for example be arranged on a distal end of an electrode lead and may be configured for coupling to tissue in the atrium. Another atrial electrode pole may be arranged proximally with respect to the first atrial electrode pole on the electrode lead and may for example be formed by a ring electrode of the electrode lead. The housing of the generator device may serve as a counter-electrode for the one or more atrial electrode poles for outputting stimulation signals, for sensing electrocardiogram signals and for measuring impedance signals.

[0042] A first ventricular electrode pole may for example be arranged on a distal end of a ventricular electrode lead and may be configured for coupling to tissue in the ventricle. Another ventricular electrode pole may be arranged proximally with respect to the first ventricular electrode pole on the ventricular electrode lead and may for example be formed by a ring electrode of the ventricular electrode lead. The housing of the generator device may serve as a counter-electrode for the one or more ventricular electrode poles for sensing electrocardiogram signals and for measuring impedance signals.

[0043] In an embodiment, the implantable medical stimulation device is a leadless device not comprising any electrode leads extending from the generator device. Herein, the generator device itself is configured for implantation in the atrium of the patient’s heart, such that the generator device upon implantation is introduced and anchored within the atrium of the patient’s heart. The at least one atrial electrode pole herein is arranged on a housing of the generator device. In addition, the implantable medical stimulation device comprises a second housing that is intended to be implanted in the ventricle and to sense, with the at least one ventricular electrode pole arranged on the second housing, ventricular signals. The generator device and the second housing are operatively connected with each other so that the signals sensed by the at least one ventricular electrode pole are available for the generator device to allow the generator device to perform the intended atrial stimulation.

[0044] 23.182P-WO | 02.10.2025 In an embodiment, the processing circuitry is configured to evaluate the momentary impedance curve only for an event sequence comprising an atrial sense followed by a ventricular sense and / or an event sequence comprising an atrial pace followed by a ventricular sense. Then, impedance curve sections comprising ventricular events followed by other ventricular events may not be evaluated and may not be used for the rate-adaptive stimulation. This ensures that a highly physiologic atrioventricular event sequence is used for the rate adaptation of the atrial stimulation.

[0045] In an embodiment, the processing circuitry is configured to store an intrinsic atrioventricular interval. This intrinsic atrioventricular interval is then used as plausibility criterion for the adaption of the paced heart rate. Typically, the intrinsic atrioventricular interval is shortened with increasing heart rate. If the intrinsic atrioventricular interval is not shortened this indicates that the patient does not require a higher heart rate, even though the impedance measurement may have indicated that a higher heart rate is required. Due to the applied plausibility criterion, a further increase of the heart rate is prevented. Expressed in other words, an increase of the paced heart rate is prevented if the intrinsic atrioventricular interval is not shortened, i.e., if the intrinsic atrioventricular interval indicates that the patient does not require a higher heart rate.

[0046] In an embodiment, the processing circuitry is configured to derive a difference parameter value indicative of a difference between the momentary impedance curve and the stored reference curve and to perform the adaption of the paced heart rate based on the difference parameter value. The difference parameter value may for example be indicative of an area in between the momentary impedance curve and the stored reference curve. In an embodiment, the difference parameter value is indicative of an area in between a first or higher-order derivative of the momentary impedance curve and of the stored reference curve. In one embodiment, the difference parameter value may relate to a difference between a maximum of the momentary impedance curve and the stored reference curve, a difference between temporal locations of maxima and minima values, a difference between an average or a median of the momentary impedance curve and the stored reference curve, a cross correlation of the momentary impedance curve and the stored reference curve, or to another

[0047] 23.182P-WO | 02.10.2025 numerical value indicative of a deviation of the momentary impedance curve from the stored reference curve.

[0048] In an embodiment, the processing circuitry is configured, based on the difference parameter value, to adapt, in particular increase, the paced heart rate in comparison to a heart rate at rest. Based on the difference parameter value, the heart rate adaption may be set, a large value for the difference parameter value indicating a large deviation of the momentary impedance curve from the stored reference curve and hence causing a large adaption of the paced heart rate, and a small value for the difference parameter value indicating a small deviation of the momentary impedance curve from the stored reference curve and hence causing a small modification of the paced heart rate.

[0049] For deriving impedance information and for monitoring an electrical impedance value, the processing circuitry, in one embodiment, is configured to generate electrical excitation signals which are output by means of the electrode arrangement. In reaction to outputting the electrical excitation signals, response signals are received, which are processed by the processing circuitry of the generator device. By correlating the electrical excitation signals and the electrical response signals received in response to the electrical excitation signals, impedance information is derived and is recorded.

[0050] An electrical excitation signal generated by the processing circuitry for outputting by the electrode arrangement may for example be a current signal produced by a defined current source, in which case the electrical response signal is a voltage signal. From the excitation signal and from the associated response signal, hence, an electrical impedance may be computed, wherein the impedance calculation is repeated throughout a cardiac cycle or a predefined portion of a cardiac cycle, in particular a partial relating to a ventricular contraction event.

[0051] In an embodiment, an electrical excitation signal generated by the processing circuitry for outputting by the electrode arrangement is a voltage signal produced by a defined voltage source, in which case the electrical response signal is a current signal. Again, from the electrical excitation signal and from the associated electrical response signal an impedance

[0052] 23.182P-WO | 02.10.2025 value may be computed, wherein the impedance calculation is repeated throughout a cardiac cycle or a predefined portion of a cardiac cycle, in particular a partial relating to a ventricular contraction event.

[0053] In an embodiment, electrical excitation signals as generated by the processing circuitry to be output by the electrode arrangement are biphasic electrical pulse signals. Such biphasic electrical pulse signals may be formed by a first pulse section having a positive amplitude and a consecutive, second pulse section having a negative amplitude, or vice versa.

[0054] In an aspect, the present invention relates to a method for operating an implantable medical stimulation device for performing a stimulation in an atrium of a patient’s heart. This method comprises the steps explained in the following. In a method step, a generator device is provided, the generator device comprising processing circuitry for processing cardiac sense signals and generating cardiac stimulation signals. In addition, an electrode arrangement for sensing cardiac signals and outputting cardiac stimulation signals is provided. In this context, the electrode arrangement comprises at least one atrial electrode pole which is configured to be placed in the atrium of the patient’s heart for sensing signals and outputting cardiac stimulation signals in the atrium of the patient’s heart. The electrode arrangement furthermore comprises at least one ventricular electrode pole which is configured to be placed in a ventricle of the patient’s heart for sensing signals in the ventricle of the patient’s heart. In another method step, a rate-adaptive cardiac stimulation is performed using the processing circuitry. In this rate-adaptive stimulation a paced heart rate is adjusted based on a load state of the patient, wherein the processing circuitry obtains a momentary impedance curve indicative of a measured impedance during a cardiac cycle, compares said momentary impedance curve to a stored reference curve and performs an adaption of the paced heart rate based on the comparison of the momentary impedance curve to the stored reference curve. The momentary impedance curve is obtained using the at least one ventricular electrode pole.

[0055] In particular, the stored reference curve is indicative of a reference impedance curve in a defined state of a patient, e.g. in a resting state.

[0056] 23.182P-WO | 02.10.2025 In particular, the paced heart rate that is adjusted based on a load state is an atrial rate.

[0057] All embodiments described above for the implantable medical stimulation device can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the described method. Likewise, all embodiments described above for the method can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the described implantable medical stimulation device.

[0058] Further details of aspects of the present invention will be explained in the following with reference to exemplary embodiments shown in the accompanying Figures. In the Figures:

[0059] Fig. 1 shows a schematic view of an implantable medical stimulation device having a generator device and electrode leads;

[0060] Fig. 2A shows a schematic drawing of the implantable medical stimulation device of Figure 1, illustrating an impedance measurement during operation;

[0061] Fig. 2B shows an impedance curve as measured during a cardiac cycle or a predefined portion of a cardiac cycle, in particular relating to a ventricular contraction event;

[0062] Fig. 3 shows a schematic drawing of a momentary impedance curve as measured during a cardiac cycle in comparison to a reference curve;

[0063] Fig. 4 shows a schematic drawing of possibilities for synchronizing the impedance measurement; and

[0064] Fig. 5 shows a schematic drawing of a synchronization of the momentary impedance curve to the reference curve according to the curves themselves.

[0065] 23.182P-WO | 02.10.2025 Subsequently, embodiments of the invention shall be described in detail with reference to the drawings. In the drawings, like reference numerals designate like structural elements.

[0066] It is to be noted that the embodiments are not limiting for the invention, but merely represent illustrative examples.

[0067] Figure 1 shows, in a schematic drawing, a human heart H comprising a right atrium RA, a right ventricle RV, a left atrium LA, and a left ventricle LV. An implantable medical stimulation device 1 is implanted in a patient, the implantable medical stimulation device 1 comprising a generator 12 connected to a ventricular lead 10 and an atrial lead 11, both extending from the generator 12 through the superior vena cava VC into the patient’s heart H. By means of the atrial lead 11, electrical signals for providing a pacing action in the heart H shall be injected into intra-cardiac tissue M and atrial sense signals may be received. By means of the ventricular lead 10, ventricular sense signals may be received.

[0068] The implantable medical stimulation device 1 as concerned herein may generally be a cardiac stimulation device such as a cardiac pacemaker device. A stimulation device of this kind comprises the generator 12, as shown in Figure 1, which may be subcutaneously implanted in a patient at a location remote from the heart H. The atrial lead 11 extends from the generator 12 into the right atrium RA of the heart H for emitting stimulation signals in the right atrium RA and / or for obtaining sense signals at one or multiple locations within the right atrium RA. The ventricular lead 11 extends from the generator 12 into the right ventricle RV of the heart H for sensing signals at one or multiple locations within the right ventricle RV. The ventricular and atrial leads 10, 11 each form a generally longitudinal, tubular lead body 100, which reaches into the heart H and is anchored at a location of interest within the heart H.

[0069] In the embodiment of Figure 1, the ventricular electrode lead 10 comprises two ventricular electrode poles 102, 103 at or in the vicinity of a distal end 101 of the lead body 100, namely a ventricular tip electrode pole 102 and a ventricular ring electrode pole 103. Similarly, the atrial electrode lead 11 comprises two atrial electrode poles 112, 113 at or in the vicinity of

[0070] 23.182P-WO | 02.10.2025 distal end 111 of the lead body 100, namely an atrial tip electrode pole 112 and an atrial ring electrode pole 113.

[0071] The ventricular electrode poles 102, 103 and the atrial electrode poles 112, 113 together form an electrode arrangement for sensing cardiac signals and for outputting cardiac stimulation signals in the course of operation of the implantable medical stimulation device 1 for performing a cardiac pacing action. Another electrode pole herein may be formed by a housing 121 of the generator device 12, the housing 121 providing a counter-electrode for any one of the electrode poles 102, 103, 112, 113 of the ventricular and atrial electrode leads 10, 11.

[0072] As schematically shown in Figure 1, the implantable medical stimulation device 1 may be in communication with an external device 2 which is external to the patient and for example is part of a home monitoring system or represents a programming device for programming the implantable medical stimulation device 1.

[0073] In addition, a motion sensor 3 may be integrated into the generator device 12 or may be implemented at another location in or on the patient, the motion sensor 3 being in communicative connection with the generator device 12 such that a processing circuitry 120 of the generator device 12 receives signals of the motion sensor 3 and evaluates signals in order to derive information with respect to a motion state of the patient.

[0074] Referring now to Figure 2A, the implantable medical stimulation device 1 generally is configured to perform a pacing action in which cardiac activity is paced to provide an antibradycardia pacing, in particular in scenarios in which intrinsic cardiac activity does not reliably occur. During operation, the processing circuitry 120 of the generator device 12 may for example be configured to sense and process cardiac sense signals, received via the electrode arrangement, and generate cardiac stimulation signals to be output via the electrode arrangement in response to sensed and processed cardiac signals.

[0075] The generator device 12 herein shall implement a cardiac rate adaption scheme, also denoted as Closed-Loop Stimulation (in short CLS), in which a paced heart rate is adapted based on

[0076] 23.182P-WO | 02.10.2025 a load state of the patient. This is based on the general principle that the paced heart rate should increase if the patient is physically and / or mentally active and hence is in a load state.

[0077] For performing the rate adaption, the processing circuitry 120 of the generator device 12 is configured to record an impedance curve, as it is shown in an example in Figure 2B. For this, the processing circuitry 120 repeatedly measures impedance values during a cardiac cycle or a predefined portion of the cardiac cycle by generating and outputting electrical excitation signals and receiving, in response, electrical response signals. By correlating the electrical excitation signals to the electrical response signals, an impedance value AZ is derived relating to an intracardiac impedance, e.g., in a certain portion of a cardiac cycle, in particular relating to ventricular contractions.

[0078] As shown in Figure 2B, the processing circuitry 120 may for example produce, as electrical excitation signals, biphasic pulses P to be output by a pair of electrode poles 102, 103, 121, for example the ventricular tip electrode pole 102 and the pole formed by the housing 121.

[0079] In an embodiment, the electrical excitation signals as generated by the processing circuitry 120 to be output by a pair of electrode poles 102, 103, 121 are current signals which are generated by a controlled current source. In this case, the electrical response signals are voltage signals. In another embodiment, the electrical excitation signals as generated by the processing circuitry 120 to be output by a pair of electrode poles 102, 103, 121 are voltage signals which are generated by a controlled voltage source. In this case, the electrical response signals are current signals.

[0080] It has been found that the intracardiac impedance, in a particular time window in relation to a QRS complex, exhibits an especially significant dependency on the patient’s load state. Hence, by measuring the impedance it may be derived whether a patient’s state differs from a defined state, e.g., a rest state, such that based on a deviation of a momentary impedance curve as measured by the processing circuitry 120 a paced heart rate may be adjusted.

[0081] Referring now to Figure 3, at rest an impedance curve may exhibit a particular shape, having, e.g., a distinct curvature and characteristic locations of a minimum and a maximum, yielding

[0082] 23.182P-WO | 02.10.2025 a reference curve AZrefRest as shown in Figure 3. In contrast, in a load state, for example a state relating to increased physical activity, a momentary impedance curve AZ1 may substantially differ from the reference curve AZrefRest.

[0083] A deviation of the momentary impedance curve AZ 1 from the reference curve AZrefRest herein may be quantified by a difference parameter value for example relating to the area Acis in between the momentary impedance curve AZ1 and the reference curve AZrefRest.

[0084] For performing a rate adaption, the reference curve AZrefRest as shown in Figure 3 may for example be recorded in an initial calibration phase and may potentially be adapted according to changing conditions during operation of the implantable medical stimulation device 1. During operation of the implantable medical stimulation device 1 for performing a pacing action, then, the momentary impedance curve AZ1, as shown in an example in Figure 3, is compared to the reference curve AZrefRest, and a difference parameter value Acis is derived indicating a deviation of the momentary impedance curve AZ1 from the reference curve AZrefRest. Based on the difference parameter value Acis, then, a rate adaption of the paced atrial rate is performed, wherein the rate adaption depends on the amount of the deviation and hence on the difference parameter value Acis.

[0085] Generally, if a large deviation of the momentary impedance curve AZ1 with respect to the reference curve AZrefRest is identified, the paced heart rate is successively adapted to increase the paced heart rate. If only a small deviation of the momentary impedance curve AZ1 with respect to the reference curve AZrefRest is identified, in contrast the paced heart rate is only slightly adapted.

[0086] As illustrated in Figure 3, the momentary impedance curve AZ1 as well as the reference curve AZrefRest are obtained in a particular time window TM encompassing ventricular activity, that is the QRS complex in the electrocardiogram signal, as schematically illustrated in Figure 3. The x axis of Figure 3 illustrates the time elapsed after an atrial pace. In the first approximately 150 ms, the heart H is in a pre-ejection state and is comparatively relaxed (illustrated by the two arrows of the schematically illustrated heart H pointing sidewards

[0087] 23.182P-WO | 02.10.2025 away from the heart H). In the time period between approximately 175 ms and 275 ms after an atrial pace, the heart H is in an ejection phase and contracts. This is illustrated by the two arrows pointing towards the schematically depicted heart H. The measurement of the momentary impedance curve AZ1 hence is synchronized to the reference curve AZrefRest, such that a sensible comparison of the momentary impedance curve AZ Ito the reference curve AZrefRest to determine the difference parameter Acis is enabled.

[0088] As shown in Figure 2 A, the ventricular electrode lead 10 is implanted in the right ventricle RV of the heart H, such that electrocardiogram signals are sensed in the ventricle, and the impedance measurement is carried out in the ventricle. As the ventricular electrode lead 10 is placed in the ventricle, electrocardiogram signal features, in particular the QRS complex, are strong in the signals sensed by the ventricular electrode lead 10, such that the QRS complex may be easily identified, and the time window TM of the momentary impedance curve AZ1 as measured using the electrode lead 10 may be easily synchronized to the reference curve AZrefRest, for example, according to the ascending branch of the R peak of the QRS complex by spanning the time window TM around the R peak.

[0089] Generally, the impedance may be measured continuously throughout successive cardiac cycles, wherein the momentary impedance curve AZ1 is identified based on a signal portion of the continuously measured impedance within the time window TM spanned to encompass the QRS complex. Other signals present in the electrocardiogram such as the P wave, the T wave, or individual features of the QRS complex may likewise be used to synchronize the momentary impedance curve AZ1 with the reference impedance curve AZrefRest.

[0090] Referring now to Figure 4, in an embodiment ventricular electrocardiogram signal features may be identified based on electrocardiogram signals as sensed in the ventricle using the ventricular electrode lead 10. For example, a QRS complex may be identified according to its R peak, wherein the location of the R peak may be used to synchronize the momentary impedance curve AZ1 to the reference curve AZrefRest, for example by spanning the window TM of the momentary impedance curve AZ1 beginning at the R peak to a later time point X or beginning at some other time point before the R peak to the later time point X, as illustrated in Figure 4. The later time point X may lie in a range between 150 ms and 550 ms

[0091] 23.182P-WO | 02.10.2025 after the R peak. The impedance herein is measured and recorded continuously using the electrode lead 11, wherein such signal portion of the impedance is used to obtain the momentary impedance curve AZ1 which corresponds to the window TM of the reference curve AZrefRest, as identified in Figure 4.

[0092] For identifying a ventricular electrocardiogram signal feature in the example of Figure 4, for example a blanking scheme may be employed, according to which signal portions not relating to ventricular activity may be blanked out, for example all signal portions relating to the atrial P wave. Such blanking may be defined for example by identifying an atrial event, for example according to an atrial pacing event or to a sensed intrinsic atrial event, wherein the blanking is chosen such that atrial contributions in the electrocardiogram signal are effectively cancelled, but ventricular contributions are kept and hence may be evaluated for determining, e.g., the location of the R peak in the QRS complex.

[0093] Referring now to Figure 5, in yet another example a synchronization of the momentary impedance curve AZ1 to the reference curve AZrefRest may take place by the curves themselves. For example, it may be observed where the momentary impedance curve AZ1 crosses the reference curve AZrefRest, i.e., where the measured momentary impedance value becomes equal to the start value of the pre-stored reference curve AZrefRest, corresponding to the location X in the example of Figure 5. The temporal location X of the crossing may be assumed as the start of the window TM of the momentary impedance curve AZ1. The synchronization of the momentary impedance curve AZ 1 to the reference curve AZrefRest hence does not involve a sensing of electrocardiogram signals, but uses an evaluation of measured impedance values.

[0094] The implantable medical stimulation device 1 beneficially is configured, in its processing circuitry 120, to carry out multiple of the described synchronization methods. If one synchronization does not yield a reliable result, for example because a ventricular electrocardiogram signal feature cannot be reliably identified, another synchronization method may be chosen.

[0095] 23.182P-WO | 02.10.2025 Based on the synchronized momentary impedance curve AZ1 in relation to the reference curve AZrefRest, a rate-adaptive cardiac stimulation is applied by adapting the paced heart rate based on the comparison of the momentary impedance curve AZ1 to the reference curve AZrefRest. For this, as described according to the example of Figure 3, a difference parameter value, corresponding for example to an area Acis in between the two curves, may be evaluated, wherein the rate adaption takes place based on the difference parameter.

[0096] Further factors may be taken into account for adapting the paced heart rate, such as an output of a motion sensor 3 (see Figure 1), such that the rate adaption may include further parameters in addition to the comparison of the momentary impedance curve AZ1 to the stored reference curve AZrefRest.

[0097] The invention is not limited to the embodiments described above, but may be implemented in an entirely different fashion.

[0098] The implantable medical stimulation device may be a device comprising electrode leads connected to a generator device. The device may comprise one or more leads, each carrying one or more electrode poles.

[0099] In other embodiments, the implantable medical stimulation device may be a leadless device, in particular a leadless pacemaker, comprising 2 entities, 1 of which being configured for implantation immediately into the atrium, in particular the right atrium, the other one of which being configured for implantation immediately into the ventricle, in particular the right ventricle.

[0100] 23.182P-WO | 02.10.2025

Claims

- 22 -Claims1. An implantable medical stimulation device (1) for stimulating an atrium (RA) of a patient’s heart (H), comprising: a generator device (12) comprising processing circuitry (120) for processing cardiac sense signals and generating cardiac stimulation signals, and an electrode arrangement for sensing cardiac signals and outputting cardiac stimulation signals, the electrode arrangement comprising i) at least one atrial electrode pole (112, 113) which is configured to be placed in the atrium (RA) of the patient’s heart (H) for sensing signals and outputting cardiac stimulation signals in the atrium (RA) of the patient’s heart (H) and ii) at least one ventricular electrode pole (102, 103) which is configured to be placed in a ventricle (RV) of the patient’s heart (H) for sensing signals in the ventricle (RV) of the patient’s heart (H), wherein the processing circuitry (120) is configured to perform a rate-adaptive cardiac stimulation in which a paced heart rate is adjusted based on a load state of the patient, wherein the processing circuitry (120) is configured to obtain a momentary impedance curve (AZ1) indicative of a measured impedance during a cardiac cycle, to compare said momentary impedance curve (AZ1) to a stored reference curve (AZrefRest) and to perform an adaption of the paced heart rate based on the comparison of the momentary impedance curve (AZ1) to the stored reference curve (AZrefRest), characterized in that the processing circuitry (120) is configured to obtain said momentary impedance curve (AZ1) using the at least one ventricular electrode pole (102).

2. The implantable medical stimulation device (1) according to claim 1, characterized in that the processing circuitry (120) is configured to synchronize the momentary impedance curve (AZ1) to the reference curve (AZrefRest) based on the occurrence of an atrial event.

3. The implantable medical stimulation device (1) according to claim 2, characterized in that the processing circuitry (120) is configured to identify the atrial event based on an outputting of an atrial pace signal (Ap) using the electrode arrangement or based on23.182P-WO | 02.10.2025a sensing of an atrial electrocardiogram signal feature using the at least one atrial electrode pole (112, 113) of the electrode arrangement.

4. The implantable medical stimulation device (1) according to claim 2 or 3, characterized in that the processing circuitry (120) is configured to synchronize the momentary impedance curve (AZ1) to the reference curve (AZrefRest) based on a defined delay time (TD) subsequent to the atrial event.

5. The implantable medical stimulation device (1) according to claim 1, characterized in that the processing circuitry (120) is configured to synchronize the momentary impedance curve (AZ1) to the reference curve (AZrefRest) based on the occurrence of an intrinsic ventricular event sensed with the at least one ventricular electrode pole (102, 103).

6. The implantable medical stimulation device (1) according to any of the preceding claims, characterized in that the processing circuitry (120) is configured to synchronize the momentary impedance curve (AZ1) to the reference curve (AZrefRest) based on a comparison of the momentary impedance curve (AZ1) and the reference curve (AZrefRest).

7. The implantable medical stimulation device (1) according to any of the preceding claims, characterized in that the processing circuitry (120) is configured to synchronize the momentary impedance curve (AZ1) to the reference curve (AZrefRest) based on comparing an impedance signal feature of the momentary impedance curve (AZ 1) to a corresponding impedance signal feature of the reference curve (AZrefRest).

8. The implantable medical stimulation device (1) according to any of the preceding claims, characterized in that the processing circuitry (120) is configured to synchronize the momentary impedance curve (AZ1) to the reference curve (AZrefRest) based on a crossing of the momentary impedance curve (AZ1) and the reference curve (AZrefRest).23.182P-WO | 02.10.20259. The implantable medical stimulation device (1) according to any of the preceding claims, characterized in that the generator device (12) does not enable a ventricular stimulation with the at least one ventricular electrode pole (102, 103).

10. The implantable medical stimulation device (1) according to any of the preceding claims, characterized in that the processing circuitry (120) is configured to evaluate the momentary impedance curve (AZ1) only for at least one the following event sequences: i) an atrial sense followed by a ventricular sense and ii) an atrial pace followed by a ventricular sense.

11. The implantable medical stimulation device (1) according to any of the preceding claims, characterized in that the processing circuitry (120) is configured to store an intrinsic atrioventricular interval and to use the intrinsic atrioventricular interval as plausibility criterion for the adaption of the paced heart rate.

12. The implantable medical stimulation device (1) according to one of the preceding claims, characterized in that the processing circuitry (120) is configured to derive a difference parameter value (Acis) indicative of a difference between the momentary impedance curve (AZ1) and the stored reference curve (AZrefRest) and to perform said adaption of the paced heart rate based on the difference parameter value (Acis).

13. The implantable medical stimulation device (1) according to claim 12, characterized in that the processing circuitry (120) is configured to derive the difference parameter value (Ads) based on at least one of a difference area between the momentary impedance curve (AZ1) and the stored reference curve (AZrefRest), a difference area between the first derivatives of the momentary impedance curve (AZ1) and the stored reference curve (AZrefRest), a cross correlation of the momentary impedance curve (AZ1) and the stored reference curve (AZrefRest), and a difference of temporal signal features in the momentary impedance curve (AZ1) and in the stored reference curve (AZrefRest).23.182P-WO | 02.10.2025- 25 -14. The implantable medical stimulation device (1) according to one of the preceding claims, characterized in that the processing circuitry (120) is configured, for obtaining said momentary impedance curve (AZ1), to generate electrical excitation signals and to provide the electrical excitation signals to the electrode arrangement for outputting into tissue and to receive, using the electrode arrangement, electrical response signals in response to the electrical excitation signals.

15. A method for operating an implantable medical stimulation device (1) for performing a stimulation of an atrium (RA) of a patient’s heart (H), the method comprising: providing a generator device (12) comprising processing circuitry (120) for processing cardiac sense signals and generating cardiac stimulation signals; providing an electrode arrangement for sensing cardiac signals and outputting cardiac stimulation signals, the electrode arrangement comprising i) at least one atrial electrode pole (112, 113) which is configured to be placed in the atrium (RA) of the patient’s heart (H) for sensing signals and outputting cardiac stimulation signals in the atrium (RA) of the patient’s heart (H) and ii) at least one ventricular electrode pole (102, 103) which is configured to be placed in a ventricle (RV) of the patient’s heart (H) for sensing signals in the ventricle (RV) of the patient’s heart (H); and performing, using the processing circuitry (120), a rate-adaptive cardiac stimulation in which a paced heart rate is adjusted based on a load state of the patient, wherein the processing circuitry (120) obtains a momentary impedance curve (AZ1) indicative of a measured impedance during a cardiac cycle, compares said momentary impedance curve (AZ1) to a stored reference curve (AZrefRest) and performs an adaption of the paced heart rate based on the comparison of the momentary impedance curve (AZ1) to the stored reference curve (AZrefRest); characterized in that said momentary impedance curve (AZ1) is obtained using the at least one ventricular electrode pole (102).23.182P-WO | 02.10.2025

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