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

Abstract

An implantable medical stimulation device (1) for performing an anti-bradycardia pacing in an atrium (RA) of a patient's heart (H) comprises a generator device (12) comprising processing circuitry (120) for processing cardiac sense signals and generating cardiac stimulation signals and a housing (121), and an electrode arrangement for sensing cardiac signals and outputting cardiac stimulation signals. The electrode arrangement comprises at least one atrial electrode pole (102, 103). 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 (ΔZ1), to compare said momentary impedance curve (ΔZ1) to a stored reference curve (ΔZrefRest) 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 configured to obtain said momentary impedance curve (ΔZ1) by conducting a unipolar impedance measurement between the at least one atrial electrode pole (102) and the housing (121).

Description

[0001] Applicant: BIOTRONIK SE & Co. KG

[0002] Date: 28.08.2025

[0003] Our Reference: 22.268P-WO

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

[0005] The instant invention relates to an implantable medical stimulation device for performing an anti -bradycardia pacing in 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 an anti -bradycardia pacing in 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 and a housing. 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.

[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. 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 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.

[0009] 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 for example is 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.

[0010] 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.

[0011] A rate-adaptive cardiac stimulation scheme is for example described in US 6,263,243. 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 a slight deviation is detected, the heart rate is only slightly adapted. If a large deviation is detected, in contrast, a large heart rate adaption takes place.

[0012] In a current rate-adaptive cardiac stimulation scheme, as for example described in US 6,263,243, 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.

[0013] 22.268P-WO | 28.08.2025 It is an object of the instant 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.

[0014] This object is achieved by means of an implantable medical stimulation device comprising the features of claim 1.

[0015] Accordingly, the processing circuitry is configured to obtain said momentary impedance curve using the at least one atrial electrode pole.

[0016] The implantable medical stimulation device is configured to provide for an anti-bradycardia pacing, wherein for performing the anti-bradycardia pacing 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.

[0017] 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.

[0018] 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.

[0019] 22.268P-WO | 28.08.2025 The processing circuitry hence stores a reference curve which is indicative of a reference impedance curve 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 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.

[0020] 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. By means of the electrode arrangement, signals may be sensed and stimulation signals may be output, wherein the sensing and the outputting takes place using 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.

[0021] 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 atrial 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.

[0022] In particular, the recording of the impedance signal and the repeatedly measurement of impedance signals is achieved by conducting a unipolar impedance measurement between the at least one atrial electrode pole and the housing of the generator device. In this case, the housing of the generator device acts as a counter electrode when measuring the impedance using the at least one atrial electrode pole.

[0023] 22.268P-WO | 28.08.2025 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 the at least one atrial electrode pole, in particular by using at least one electrode pole of an atrial electrode lead only together with the housing as counter electrode in a unipolar measurement configuration, 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 atrial electrode pole in a unipolar measurement. It hence becomes possible to apply a rate-adaptive cardiac stimulation in a one-chamber atrial pacemaker employing a stimulation and sensing only in one chamber, i.e., in the (right) atrium of the patient's heart.

[0024] In particular, a unipolar measurement of the impedance may be achieved by measuring the impedance between the at least one atrial electrode pole and the housing as counter electrode pole. In particular, a unipolar measurement configuration may be achieved by configuring the implantable medical device such that the housing of the implantable medical device acts as a counter electrode to the at least one atrial electrode pole such that the impedance is, in particular, measured using the atrial electrode lead only and the housing. In this case, the at least one atrial electrode pole is connected to a first electrical potential and the housing is connected to a second electrical potential, and the impedance measurement may take place via the potential difference of the first and second electrical potentials.

[0025] In particular, the implantable medical stimulation device may be operated in a so-called AAI mode, indicative of a mode in which a stimulation as well as a sensing takes place in the atrium and, in addition, an inhibition is applied which indicates that the stimulation device suppresses a stimulation pulse if a natural atrial contraction is sensed (Simply put, the stimulation device only comes into action when the heart rate falls below a defined frequency to perform an anti-bradycardia pacing).

[0026] Typically, a rate-adaptive cardiac stimulation by measuring a momentary impedance curve and by comparing such momentary impedance curve to a reference curve is employed in an implantable medical stimulation device using an electrode arrangement which allows for a sensing of signals (also) in the ventricle. When sensing electrocardiogram signals in the

[0027] 22.268P-WO | 28.08.2025 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.

[0028] As the momentary impedance curve shall be compared to a reference curve in order to perform an adaption of the paced heart 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, synchronisation 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] It generally can be expected that the measured impedance in the atrium is at least similar to the impedance if it would be measured in the ventricle. However, because with the implantable medical stimulation device electrocardiogram signals are sensed using an atrial sensing, it may occur that a ventricular electrocardiogram signal feature such as the QRS complex may not be as reliably measured, as it is the case when sensing electrocardiogram signals in the ventricle, because ventricular signals from the perspective of the atrial electrode poles occur in the far field or even cannot be sensed at all. Therefore, it may become necessary to apply a particular synchronization scheme in order to synchronize the momentary impedance curve as measured in the atrium to the reference curve.

[0030] 22.268P-WO | 28.08.2025 In one embodiment, the processing circuitry is configured to synchronize the momentary impedance curve to the reference curve based on the occurrence of an atrial event or a ventricular event. Such atrial event or ventricular 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 or ventricular event may relate to a pacing event.

[0031] In one embodiment, if the momentary impedance curve is synchronized with the help of an atrial sense event, recording the impedance curve can be started directly after the atrial sense event. Thus, in contrast to an impedance measurement in the presence of, for instance, ventricular pacing, here, recording of an impedance curve does not necessarily 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 more reliable impedance signal is recorded which extends, on the one hand, over a longer time period and, on the other hand, fully 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.

[0032] In one 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 AAI 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 an atrial blanking interval has passed to avoid an undesired superposition of the atrial stimulation pulse and atrial signals, i.e., a cross talk between the atrial stimulation pulse (or its post-potential) and

[0033] 22.268P-WO | 28.08.2025 an atrial sense channel that is intended to sense “real” atrial signals. Thus, the time delay serves for reducing the risk of sensing and recording atrial artefacts.

[0034] In one 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.

[0035] 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 may be expected.

[0036] In one embodiment, if the atrial event is a paced event, the delay time may be an atrial blanking interval. In this case, the delay time may lie in a range from 10 ms to 40 ms, for example 20 ms, and marks the start of the window of the momentary impedance curve subsequent to the identified paced atrial event.

[0037] In one embodiment, if the atrial event is a sensed or a paced event, the delay time may be an estimated atrioventricular conduction time. In this case, the delay time may be dynamically adjustable, in particular based on the paced heart rate. The atrioventricular conduction time may lie in a range between 100 ms to 200 ms, in particular 150 ms to 180 ms, for example 170 ms and marks the start of the window of the momentary impedance curve subsequent to the identified sensed or paced atrial event.

[0038] In one embodiment, the window of the momentary impedance curve may for example have a duration between 300 ms and 700 ms, in particular 300 ms and 500 ms, in particular between 350 ms and 450 ms, for example 400 ms.

[0039] 22.268P-WO | 28.08.2025 In one embodiment, the processing circuitry is configured to identify a ventricular event based on a sensing of a ventricular electrocardiogram signal feature using the at least one atrial electrode pole of the electrode arrangement. As, using the at least one atrial electrode pole implanted (in an implanted state of the implantable medical stimulation device) in the atrium of the patient's heart, electrocardiogram signals relating to ventricular activity are sensed in the far field, such ventricular electrocardiogram signal feature, for example corresponding to a QRS complex, may be weak. For sensing such ventricular electrocardiogram signal feature, hence, a particular processing may be employed, for example a blanking scheme which blanks out portions in the electrocardiogram signal not relating to ventricular activity, such as the atrial P wave. By blanking out stronger signal contributions, ventricular signal contributions may be enhanced.

[0040] For example, by means of the ventricular electrocardiogram signal feature relating to the QRS complex the R peak may be identified. The momentary impedance curve may then be synchronized to the reference curve by spanning a window around the R peak. For this, the impedance for example may be continuously measured and recorded, wherein a defined portion of the impedance around the ventricular electrocardiogram signal feature is then used to obtain the momentary impedance curve, the portion temporally corresponding to the window of the reference curve such that a sensible comparison is enabled.

[0041] In one embodiment, the processing circuitry is configured to synchronize the momentary impedance curve to the reference curve based on a comparison of the momentary impedance 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

[0042] 22.268P-WO | 28.08.2025 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.

[0043] The processing circuitry, in one embodiment, is configured for computing different measures for synchronizing the momentary impedance curve to the reference curve, for example based on atrial events and ventricular events and 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.

[0044] In one embodiment, the implantable medical stimulation device comprises an 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. 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.

[0045] 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 outputting stimulation signals, for sensing electrocardiogram signals and for measuring impedance signals.

[0046] In one 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

[0047] 22.268P-WO | 28.08.2025 patient's heart. The at least one atrial electrode pole herein is arranged on a housing of the generator device.

[0048] In one 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. The area in between the momentary impedance curve and the stored reference curve corresponds to a difference between the area under the momentary impedance curve and the area under the stored reference curve. In one 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 maximum and minimum 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 numerical value indicative of a deviation of the momentary impedance curve from the stored reference curve.

[0049] In one 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.

[0050] 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

[0051] 22.268P-WO | 28.08.2025 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.

[0052] 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.

[0053] In another 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 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.

[0054] In one 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.

[0055] In another aspect, a method for operating an implantable medical stimulation device for performing an anti-bradycardia pacing in an atrium of a patient’s heart comprises: providing a generator device comprising processing circuitry for processing cardiac sense signals and generating cardiac stimulation signals and a housing; providing an electrode arrangement for sensing cardiac signals and outputting cardiac stimulation signals, the electrode arrangement comprising at least one atrial electrode pole which is configured to be placed

[0056] 22.268P-WO | 28.08.2025 in the atrium of the patient’s heart for sensing signals and outputting cardiac stimulation signals in the atrium of the patient’s heart; and performing, using the processing circuitry, 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 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 by conducting a unipolar impedance measurement between the at least one atrial electrode pole and the housing.

[0057] The advantages and advantageous embodiments described above for the implantable medical stimulation device equally apply also to the method, such that it shall be referred to the above in this respect.

[0058] The idea of the invention shall subsequently be described in more detail with reference to the embodiments shown in the figures. Herein:

[0059] Fig. 1 shows a schematic view of an exemplary 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 Fig. 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 a one-chamber implantable medical stimulation device according to an embodiment of the present invention;

[0064] 22.268P-WO | 28.08.2025 Fig. 5 shows a schematic drawing of a momentary impedance curve and a reference curve, synchronized according to an atrial event;

[0065] Fig. 6 shows a schematic drawing of possibilities for synchronizing the impedance measurement; and

[0066] Fig. 7 shows a schematic drawing of a synchronization of the momentary impedance curve to the reference curve according to the curves themselves.

[0067] Subsequently, illustrative examples and embodiments of the invention shall be described in detail with reference to the drawings. In the drawings, like reference numerals designate like structural elements.

[0068] It is to be noted that the embodiments are not limiting for the invention, but merely represent illustrative examples.

[0069] Fig. 1 shows, in a schematic drawing, the human heart H comprising the right atrium RA, the right ventricle RV, the left atrium LA and the left ventricle LV. An exemplary implantable medical stimulation device 1 is implanted in a patient, the implantable medical stimulation device 1 comprising a generator 12 connected to leads 10, 11 extending from the generator 12 through the superior vena cava into the patient's heart H. By means of the leads 10, 11, electrical signals for providing a pacing action in the heart H shall be injected into intra-cardiac tissue M potentially at different locations within the heart, and sense signals may be received.

[0070] An 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 may comprise a generator 12, as shown in Fig. 1, which may be subcutaneously implanted in a patient at a location remote from the heart H, one or multiple leads 10, 11 extending from the generator 12 into the heart H for emitting stimulation signals in the heart H or for obtaining sense signals at one or multiple locations from the heart H. The leads 10, 11 each

[0071] 22.268P-WO | 28.08.2025 form a generally longitudinal, tubular body 100, which reaches into the heart H and is anchored at a location of interest within the heart H.

[0072] In the embodiment of Fig. 1, the electrode leads 10, 11 may comprise electrode poles 102, 103 at or in the vicinity of the distal end 101 of the respective lead body 100, the electrode poles 102, 103 together forming 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 the housing 121 of the generator device 12, the housing 121 providing a counter-electrode for any one of the electrode poles 102, 103 of the electrode leads 10, 11.

[0073] As schematically shown in Fig. 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.

[0074] 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.

[0075] Referring now to Fig. 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.

[0076] 22.268P-WO | 28.08.2025 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 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 Fig. 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 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 Fig. 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 a tip electrode pole 102 and the pole formed by the housing 121.

[0079] In one 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] 22.268P-WO | 28.08.2025 Referring now to Fig. 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 a reference curve AZrefRest as shown in Fig. 3. In contrast, in a load state, for example a state relating to increased physical activity, a momentary impedance curve AZ 1 may substantially differ from the reference curve AZrefRest.

[0082] 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.

[0083] For performing a rate adaption, a reference curve AZrefRest as shown in Fig. 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, a momentary impedance curve AZ1, as shown in an example in Fig. 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 is performed, wherein the rate adaption depends on the amount of the deviation and hence on the difference parameter value Acis.

[0084] 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.

[0085] As illustrated in Fig. 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 Fig. 3. The measurement of the momentary impedance curve AZ1 hence is synchronized to the

[0086] 22.268P-WO | 28.08.2025 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.

[0087] In the example of Fig. 2A, the 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 electrode lead 10 is placed in the ventricle, electrocardiogram signal features, in particular the QRS complex, are strong in the signals sensed by the 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 R peak of the QRS complex by spanning the time window TM around the R peak.

[0088] Generally, the impedance may be measured continuously throughout successive cardiac cycles, wherein the momentary impedance curve AZ 1 is identified based on a signal portion of the continuously measured impedance within the time window TM spanned to encompass the QRS complex.

[0089] Fig. 4 shows an embodiment of the present invention. Referring now to Fig. 4, if, in contrast to the example of Fig. 2A, a one-chamber implantable medical installation device 1 is used having only a single electrode lead 11 implanted in the right atrium RA, the outputting of stimulation signals as well as a signal sensing and an impedance measurement takes place in the right atrium RA using the electrode lead 11. The electrode lead 11 herein comprises a lead body 110 extending from the generator device 12, the lead body 110 forming a distal end 111 carrying an electrode pole 112, for example in the shape of a helical screw to be engaged with tissue in the right atrium RA for coupling to the tissue. A further electrode pole 113 is arranged proximally with respect to the electrode pole 112 on the lead body 110 and is formed for example by a ring electrode circumferentially extending about the lead body 110. Both electrode poles 112, 113, upon implantation of the electrode lead 11 in the heart H, rest within the right atrium RA and hence function as atrial electrode poles.

[0090] 22.268P-WO | 28.08.2025 As, in the example of Fig. 4, electrocardiogram signals are sensed in the right atrium RA by the electrode arrangement formed by the electrode poles 112, 113 in the right atrium RA together with a counter-electrode pole 121 formed by the housing of the generator device 12, it can be expected that sensed electrocardiogram signals will predominantly contain signal contributions from the atrium, whereas signal contributions from the ventricles are comparatively weak or, in general, cannot be sensed at all.

[0091] Impedance measurements, in the example of Fig. 4, are conducted using the electrode lead 11, for example the distal electrode pole 112, together with the counter-electrode formed by the electrode pole 121 of the housing of the generator device 12, as illustrated in Fig. 4. It can be expected that a measured impedance, obtained using the electrode lead 11, is at least similar to the impedance as measured using a ventricular electrode lead 10, as in the example of Fig. 2 A.

[0092] Referring now to Fig. 5, also for the implantable medical stimulation device 1 of the example of Fig. 4 a momentary impedance curve AZ1 as measured using the electrode lead 11 must be synchronized to a reference curve AZrefRest in order to allow for a sensible comparison of the momentary impedance curve AZ1 to the reference curve AZrefRest.

[0093] For the synchronization, different schemes are possible.

[0094] For example, as illustrated in Fig. 5, the window TM of the momentary impedance curve AZ1 may be synchronized to the window of the reference curve AZrefRest by applying a defined time delay TD to a prior atrial event. The atrial event may be an atrial pace event Ap, corresponding to the outputting of an atrial stimulation device using the electrode lead 11. In another embodiment, the atrial event may be an atrial sense event, sensed for example according to an atrial P wave identified in the electrocardiogram signal which is obtained using the electrode lead 11.

[0095] The time delay TD may be prestored and may have a value for example in between 100 ms and 200 ms, in particular between 150 ms to 180 ms, for example 170 ms.

[0096] 22.268P-WO | 28.08.2025 Also, the length of the measurement window TM may be predefined and programmed into the processing circuitry 120. The length of the window TM of the momentary impedance curve AZ1, corresponding to the length of the window of the reference curve AZrefRest, may have a value in between 300 ms and 700 ms, in particular 300 ms to 500 ms, in particular between 350 ms to 450 ms, for example 400 ms, such that the window TM can be assumed to encompass a time range of ventricular activity subsequent to an atrial event.

[0097] Referring now to Fig. 6, in one embodiment ventricular electrocardiogram signal features may be identified based on electrocardiogram signals as sensed in the atrium using the electrode lead 11. 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 AZ Ito the reference curve AZrefRest, for example by spanning the window TM of the momentary impedance curve AZ1 around the R peak, as illustrated in Fig. 6. 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 AZ 1 which corresponds to the window TM of the reference curve AZrefRest, as identified in Fig. 6.

[0098] For identifying a ventricular electrocardiogram signal feature in the example of Fig. 6, 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.

[0099] Referring now to Fig. 7, 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 Fig. 7. The temporal location X of the crossing may be

[0100] 22.268P-WO | 28.08.2025 assumed as the start of the window TM of the momentary impedance curve AZ 1. The synchronization of the momentary impedance curve AZ1 to the reference curve AZrefRest hence does not involve a sensing of electrocardiogram signals, but uses an evaluation of measured impedance values.

[0101] 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.

[0102] 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 Fig. 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.

[0103] Further factors may be taken into account for adapting the paced heart rate, such as an output of a motion sensor 3 (see Fig. 1), such that the rate adaption may include further parameters in addition to the comparison of the momentary impedance curve AZ 1 to the stored reference curve AZrefRest.

[0104] The invention is limited to the embodiments described abover, but may be implemented in an entirely different fashion.

[0105] 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.

[0106] 22.268P-WO | 28.08.2025 In other embodiments, the implantable medical stimulation device may be a leadless device, in particular a leadless pacemaker, configured or implantation immediately into the atrium, in particular the right atrium.

[0107] 22.268P-WO | 28.08.2025 List of Reference Numerals

[0108] I Implantable medical stimulation device

[0109] 10 Lead

[0110] 100 Lead body

[0111] 101 Distal end

[0112] 102 Electrode pole

[0113] 103 Electrode pole

[0114] I I Lead

[0115] 110 Lead body

[0116] I I I Distal end

[0117] 112 Electrode pole

[0118] 113 Electrode pole

[0119] 12 Generator

[0120] 120 Processing circuitry

[0121] 121 Housing

[0122] 2 External device

[0123] 3 Motion sensor

[0124] Acls Difference parameter value

[0125] Ap Atrial pace signal

[0126] AZi Impedance curve

[0127] AZrefRest Reference curve

[0128] H Heart

[0129] LA Left atrium

[0130] LV Left ventricle

[0131] M Intra-cardiac tissue (myocardium)

[0132] P Excitation pulse

[0133] RA Right atrium

[0134] RV Right ventricle

[0135] TD Delay time

[0136] TM Measurement window

[0137] X Start point

[0138] 22.268P-WO | 28.08.2025

Claims

Claims1. An implantable medical stimulation device (1) for performing an anti-bradycardia pacing in 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 a housing (121), and an electrode arrangement for sensing cardiac signals and outputting cardiac stimulation signals, the electrode arrangement comprising at least one atrial electrode pole (102, 103) which is configured to be placed in the atrium (RA) of the patient’s heart for sensing signals and outputting cardiac stimulation signals in the atrium (RA) 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) by conducting a unipolar impedance measurement between the at least one atrial electrode pole (102) and the housing (121).

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 or a ventricular event.

3. The implantable medical stimulation device (1) according to claim 2, characterized in that the processing circuitry (120) is configured to identify an atrial event based on an outputting of an atrial pace signal (Ap) using the electrode arrangement or based on22.268P-WO | 28.08.2025a sensing of an atrial electrocardiogram signal feature using the at least one atrial electrode pole (102, 103) 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 one of claims 2 to 4, characterized in that the processing circuitry (120) is configured to identify a ventricular event based on a sensing of a ventricular electrocardiogram signal feature using the at least one atrial electrode pole (102, 103) of the electrode arrangement.

6. The implantable medical stimulation device (1) according to one 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 one 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 (AZ1) to a corresponding impedance signal feature of the reference curve (AZrefRest).

8. The implantable medical stimulation device (1) according to one 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).22.268P-WO | 28.08.20259. The implantable medical stimulation device (1) according to one of claims 1 to 8, characterized in that the implantable medical stimulation device (1) comprises an electrode lead (11) comprising said at least one atrial electrode pole (102, 103), the electrode lead (11) comprising a distal end (101) configured for implantation in the atrium (RA) of the patient’s heart (H).

10. The implantable medical stimulation device (1) according to one of claims 1 to 8, characterized in that the implantable medical stimulation device (1) is a leadless device, wherein the generator device (12) is configured for implantation in the atrium (RA) of the patient’s heart (H), the at least one atrial electrode pole (102, 103) being arranged on a housing of the generator device (12).

11. 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).

12. The implantable medical stimulation device (1) according to claim 11, characterized in that the processing circuitry (120) is configured to derive the difference parameter value (Ads) based on an area in between the momentary impedance curve (AZ1) and the stored reference curve (AZrefRest).

13. The implantable medical stimulation device (1) according to claim 11 or 12, characterized in that the processing circuitry (120) is configured to increase, based on the difference parameter value (Ads), said paced heart rate in comparison to a heart rate at rest.

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, to generate electrical excitation signals and to provide the electrical excitation signals to the electrode arrangement for22.268P-WO | 28.08.2025outputting 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 an anti -bradycardia pacing in 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 and a housing (121); providing an electrode arrangement for sensing cardiac signals and outputting cardiac stimulation signals, the electrode arrangement comprising at least one atrial electrode pole (102, 103) which is configured to be placed in the atrium (RA) of the patient’s heart for sensing signals and outputting cardiac stimulation signals in the atrium (RA) 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 by conducting a unipolar impedance measurement between the at least one atrial electrode pole (102) and the housing (121).22.268P-WO | 28.08.2025

Images