Implantable medical device for performing a cardiac stimulation

Abstract

An implantable medical device (1) for performing a cardiac stimulation comprises a generator device (12) comprising a processing circuitry (120) for processing electrical signals, an electrode lead (10, 11) connected to the generator device (12) and extending from the generator device (12), the electrode lead (10) comprising a lead body (100) forming a distal end (101) to be arranged on cardiac tissue within a patient's heart (H), and an electrode pole arrangement comprising at least three electrode poles (102, 103, 121). The processing circuitry (120) is configured to generate an electrical stimulation signal (P) and to provide the electrical stimulation signal (P) to said electrode pole arrangement for stimulating cardiac activity. The processing circuitry (120) furthermore is configured to measure at least two electrical response signals (S, SA, SB, SC) indicative of a stimulated cardiac activity in response to said electrical stimulation signal (P) using at least two different pairs of electrode poles out of said at least three electrode poles (102, 103, 121) and to derive information indicative of a stimulation effectiveness of said electrical stimulation signal (P) based on said at least two electrical response signals (S, SA, SB, SC).

Description

[0001] Implantable medical device for performing a cardiac stimulation

[0002] The present invention relates to an implantable medical device for performing a cardiac stimulation according to the preamble of claim 1 and to a method for operating an implantable medical device for performing a cardiac stimulation.

[0003] An implantable medical device of this kind comprises a generator device comprising processing circuitry for processing electrical signals, an electrode lead connected to the generator device and extending from the generator device, and an electrode pole arrangement comprising at least three electrode poles. The electrode lead comprises a lead body forming a distal end to be arranged on cardiac tissue within a patient’s heart. The processing circuitry is configured to generate an electrical stimulation signal and to provide the electrical stimulation signal to said electrode pole arrangement for stimulating cardiac activity.

[0004] With common electrode arrangements of leads of implantable medical stimulation devices, an injection of stimulation signals generally is possible at the surface of intra-cardiac tissue, an electrode being in contact with intra-cardiac tissue in order to allow an injection of stimulation energy into the tissue. With new approaches for example for providing a stimulation in case of a so-called left bundle block, it may be desired to provide for an excitation in a localized fashion in the region of the so-called left bundle branch, also denoted as left bundle branch area pacing (LBBAP), which requires to engage with intra-cardiac tissue in the range of the septum of the heart and to place an electrode in the vicinity of the left bundle branch, such that stimulation energy may be specifically injected into the conductive structure of the left bundle branch.

[0005] To be able to perform a left bundle branch area pacing and to in this way provide for a left ventricular stimulation in case of a so-called left bundle block, an electrode pole arranged on an electrode lead shall engage with intra-cardiac tissue in the range of the septum of the heart in the vicinity of the left bundle branch. Upon implantation of the electrode lead a stimulation signal is generated at an energy that allows for a reliable stimulation by coupling to the conductive structure of the left bundle branch and by hence stimulating the left ventricle. Herein, in order to determine a suitable stimulation energy, for example a so-called capture threshold test is performed in which the signal energy of the stimulation signal is adaptively changed to determine such minimum signal energy which still allows for a reliable capture, i.e., a coupling of energy to the conductive structure to allow for an effective stimulation.

[0006] For example, within a capture threshold test the signal energy of the stimulation signal is progressively reduced from a maximum starting energy until no capture is observed any longer. The value of the signal energy at which no capture is observed any more is determined to correspond to a capture threshold. By then setting the signal energy of a stimulation signal for subsequent operation to a value above the threshold, the stimulation signal is configured to allow for a reliable capture while preserving energy resources of the implantable medical device.

[0007] Within current capture threshold tests, it generally is monitored whether a capture is obtained or not when adaptively changing the signal energy of a stimulation signal. There however is a desire to distinguish between different types of a capture in order to be able to assess whether a specific region of the patient's heart is stimulated or not, such as the left ventricle within a left bundle branch area pacing.

[0008] WO 2008 / 058265 A2 discloses a cardiac stimulation system and method which allow to deliver a left ventricle stimulator from a right ventricle lead system in the right ventricle chamber, into a right side of the septum at a first location, and transmuscularly from the first location to a second location along the left side of the septum. The left ventricle stimulator is fixed at the second location for transmuscular stimulation of the left ventricular conduction system. A biventricular stimulation system further includes a right ventricle stimulator also delivered by the right ventricle lead system to the first location along the right side of the septum for right ventricular stimulation. US 2009 / 0276000 Al discloses a method for delivering physiological pacing by selecting an electrode implant site for sensing cardiac signals, which is in proximity to the hearts intrinsic conduction system. An arrangement of multiple electrodes herein is arranged on a tip of a lead.

[0009] It is an object of the instant invention to provide an implantable medical device for performing a cardiac stimulation and a method for operating an implantable medical device for performing a cardiac stimulation which allow for an easy, controllable and reliable stimulation of cardiac tissue, in particular for causing a left ventricular stimulation.

[0010] This object is achieved by means of an implantable medical device comprising the features of claim 1.

[0011] In one aspect, an implantable medical device for performing a cardiac stimulation comprises a generator device comprising a processing circuitry for processing electrical signals, an electrode lead connected to the generator device and extending from the generator device, the electrode lead comprising a lead body forming a distal end to be arranged on cardiac tissue within a patient’ s heart, in particular in the septum of a patient’ s heart, and an electrode pole arrangement comprising at least three electrode poles, wherein the processing circuitry is configured to generate an electrical stimulation signal and to provide the electrical stimulation signal to said electrode pole arrangement for stimulating cardiac activity. The processing circuitry is configured to measure at least two electrical response signals indicative of a stimulated cardiac activity in response to said electrical stimulation signal using at least two different pairs of electrode poles out of said at least three electrode poles and to derive information indicative of a stimulation effectiveness of said electrical stimulation signal based on said at least two electrical response signals.

[0012] The implantable medical device comprises a generator device and an electrode lead connected to the generator device. The electrode lead extends from the generator device and comprises a lead body forming a distal end to be arranged on cardiac tissue within a patient's heart, in particular in the septum of a patient’s heart. An electrode pole arrangement, comprising electrode poles arranged on the electrode lead and / or on the generator device and / or on another electrode lead connected to the generator device, is used to output electrical stimulation signals such that by means of the electrode pole arrangement an electrical stimulation of a desired cardiac region, in particular the septum of a patient’s heart, may be achieved.

[0013] Generally, the processing circuitry generates, during operation, electrical stimulation signals and provides the electrical stimulation signals to the electrode pole arrangement for stimulating cardiac activity. By means of the electrical stimulation signals a cardiac stimulation, in particular a cardiac pacing, may be established, the implantable medical device for example functioning as a CRT device, in particular a CRT-P or CRT-D device (CRT: cardiac resynchronization therapy). In another embodiment, the implantable medical device may function as an IPG or ICD device (IPG: implantable pulse generator; ICD: implantable cardioverter defibrillator).

[0014] Prior to operation, in an initial calibration phase, or repeatedly during operation it may be desired to evaluate whether an effective cardiac stimulation of a desired kind is obtained in response to an electrical stimulation signal. It herein is desired to be able to evaluate a cardiac stimulation in order to distinguish between different types of stimulations, for example no capture (corresponding to a situation in which no identifiable stimulation is observed in response to the output of an electrical stimulation signal), a selective left bundle branch area pacing (selective LBBAP, corresponding to a stimulation of only the left bundle branch resulting in a stimulated left ventricular activity), a non-selective left bundle branch area pacing (non-selective LBBAP, resulting in a stimulation of the left bundle branch and the right bundle branch and / or the septum), or a right bundle branch area pacing (RBBAP, corresponding to a stimulation of the right bundle branch and / or or the septum alone, without a stimulation of the left bundle branch).

[0015] In particular in the context of a left bundle branch area pacing (LBBAP) it may be desirous to be able to determine whether an injected stimulation signal in fact results in an effective stimulation of the left bundle branch and a corresponding left ventricular activity. If no such stimulation is obtained, it may be necessary to adapt a stimulation energy such that a reliable stimulation and hence a capture of the left bundle branch is (again) obtained.

[0016] To be able to assess a stimulation effectiveness, i.e., to examine whether the output of an electrical stimulation signal effectively results in a desired stimulated cardiac activity, the processing circuitry is configured to measure at least two electrical response signals indicative of a stimulated cardiac activity in response to an electrical stimulation signal using at least two different pairs of electrode poles out of said at least three electrode poles. The different pairs of electrode poles, due to a spatial separation of the electrode poles of the electrode arrangement, span different signal reception vectors and hence couple in a spatially differentiated manner to tissue in an implanted state of the implantable medical device. By recording different electrical response signals using the different pairs of electrode poles, hence, information is obtained about a spatially differentiated response to the electrical stimulation signal.

[0017] As the different pairs of electrode poles span different signal reception vectors and hence are indicative of an electrical signal response in different areas, by assessing the different electrical response signals it may be evaluated in which areas or in which conductive structures the electrical stimulation signal causes an electrical stimulation and in which areas or in which conductive structures the electrical stimulation signal does not cause an electrical stimulation.

[0018] By recording, in response to and in correlation with the outputting of an electrical stimulation signal, multiple electrical response signals obtained using different pairs of electrode poles of the electrode pole arrangement, thus, spatially differentiated response information is obtained. By assessing the different response signals, for example a response signal indicative of a response in a certain area or in relation to a certain conductive structure (such as the left bundle branch), it may be evaluated whether in a particular area or in a particular conductive structure a desired, effective stimulation is achieved.

[0019] By deriving information indicative of a stimulation effectiveness, i.e., information whether a particular desired stimulation is effectively achieved, based on at least two electrical response signals measured in response to an electrical stimulation signal, it may be evaluated whether an electrical stimulation signal yields a stimulation of a desired kind, namely of a particular spatial region or conductive structure, such as the left bundle branch. This is possible in that the different electrical response signals are measured by different pairs of electrode poles spanning different signal reception vectors, hence allowing for a spatially differentiated measurement of response signals and hence a spatially differentiated assessment of an electrical stimulation in certain regions or certain conductive structures.

[0020] In one embodiment, a first of the at least three electrode poles is arranged on the distal end of the lead body and is configured to be inserted into cardiac tissue. For example, the first electrode pole is arranged on the distal end of the lead body and is configured to be inserted into cardiac tissue to operatively engage with a conductive structure of the left bundle branch in intra-cardiac tissue. The first electrode pole may for example have the shape of a helical screw which may be inserted into intra-cardiac tissue by screwing the helical screw into tissue. In another embodiment, the first electrode pole may have the shape of a pike or a tine protruding from the distal end of the lead body and being configured for insertion into intracardiac tissue.

[0021] In one embodiment, a second of the at least three electrode poles is arranged on the lead body at a location proximal to the first of the at least three electrode poles. The second electrode pole may for example have the shape of a ring electrode extending circumferentially about the lead body.

[0022] A third of the at least three electrode poles may for example be arranged on the generator device, formed for example by the housing or a housing section of the generator device.

[0023] Further electrode poles in the electrode pole arrangement may be present and may be arranged on the lead body of the electrode lead or on the housing of the generator device or on another lead connected to the generator device.

[0024] In one embodiment, a first pair of electrode poles is formed by the first of the at least three electrode poles and the third of the at least three electrode poles. A second pair of electrode poles is formed by the second of the at least three electrode poles and the third of the at least three electrode poles. The processing circuitry herein is configured to measure a first electrically response signal using the first pair and a second electrical response signal using the second pair.

[0025] The first pair of electrode poles spans a signal reception vector in between the first electrode pole at the distal end of the electrode lead and the third electrode pole arranged on the housing of the generator device. As the first electrode pole preferably is configured for insertion into cardiac tissue such that it reaches towards the left bundle branch and hence establishes a coupling to the left bundle branch, by means of the signal reception vector spanned by the first pair of electrode poles in particular a response signal indicative of an electrical stimulation of the left bundle branch may be obtained.

[0026] The second pair of electrode poles spans a signal reception vector in between the second electrode pole at a proximal location on the electrode lead and the third electrode pole arranged on the housing of the generator device. The second electrode pole, formed for example by a ring electrode proximally with respect to the first electrode pole, may for example rest, in an implanted state of the implantable medical device, in proximity to the right bundle branch such that by means of the second pair of electrode poles in particular a response signal indicative of an electrical stimulation of the right bundle branch may be obtained.

[0027] In addition, a third pair of electrode poles may be formed by the first of the at least three electrode poles and the second of the at least three electrode poles. The processing circuitry thus is configured to measure a third electrical response signal using the third pair. The third pair of electrode poles spans a signal reception vector in between the first electrode pole and the second electrode pole, that is between the first electrode pole at the distal end of the electrode lead and the second electrode pole arranged proximally with respect to the first electrode pole, such that the third signal reception vector may for example span across conductive structures of the left bundle branch and right bundle branch. For deriving information indicative of a stimulation effectiveness, for example, the different response signals may be put into relation with one another. For example, signal levels of the different response signals may be compared in order to assess a stimulated activity in response to the outputting of the electrical stimulation signal. If for example one response signal yields a rather large signal level, whereas another response signal yields a comparatively low signal level, this may indicate that a conductive structure associated with the one response signal, but not a conductive structure associated with the other response signal has been stimulated by the electrical stimulation signal.

[0028] In one embodiment, the processing circuitry is configured to measure the at least two electrical response signals using different pairs of electrode poles at a defined timing distance with respect to the electrical stimulation signal. The timing distance may for example correspond to the length of a blanking window in a measurement channel following the outputting of the electrical stimulation signal. The measurements may take place in a defined time window, wherein all response signals are recorded in the same time window in order to allow for a comparison of the different response signals measured using the different pairs of electrode poles of the electrode pole arrangement.

[0029] For assessing the at least two electrical response signals to derive information indicative of a stimulation effectiveness of the electrical stimulation signal, a signal processing of the at least two electrical response signals may be applied to determine one or multiple characteristic metrics for at least one of the at least two electrical response signals. In particular, for one or all of the at least two electrical response signals a maximum or minimum amplitude value may be determined. Alternatively or in addition, a temporal location of a zero-crossing or a maximum or minimum amplitude value may be determined. Yet alternatively or in addition, an area under a curve of the respective electrical response signal may be determined. Yet alternatively or in addition, a signal width of a defined portion of the respective electrical response signal may be determined, for example a temporal width in between zero-crossings of the respective electrical response signal. Yet alternatively or in addition, a derivative value of the respective electrical response signal may be determined, for example a maximum or minimum derivative value of the respective electrical response signal to assess a steepness of the curve. Other characteristic metrics of a respective electrical response signal may be determined and assessed, for example relating to the positions of zero-crossings, threshold-crossings, maximum or minimum values, area values under certain portions of the curve, first, second or third derivative values or the like.

[0030] In one embodiment, the processing circuitry is configured to compare at least one of the at least two electrical response signals to a reference curve and to derive the information indicative of a stimulation effectiveness of the electrical stimulation signal based on the comparison. The reference curve may for example be predefined and stored within the processing circuitry, namely within an electronic memory of the processing circuitry. In one embodiment, the reference curve may correspond to an electrical response signal as obtained for one or multiple prior stimulation signals, for example an average of multiple prior electrical response signals.

[0031] Based on the comparison, for example certain characteristic measures may be determined indicative of a difference between an electrical response signal and the reference curve. For example, a difference in maximum or minimum values, a difference in temporal locations of zero-crossings or maximum or minimum values, and / or a difference area in between the electrical response signal and the reference curve may be determined.

[0032] In one embodiment, the processing circuitry is configured to compare the at least two electrical response signals to each other and to derive said information indicative of a stimulation effectiveness of said electrical stimulation signal based on the comparison. For example, certain characteristic metrics of the different response signals may be compared to each other, for example relating to a maximum or minimum amplitude value, a derivative value, temporal locations of zero-crossings or a maximum or minimum amplitude value, an area metrics or the like. By comparing certain parameters, preferably a set of predefined parameters, the response signals may be put into relation with one another, such that it may be assessed whether one response signal indicates an effective stimulation in a certain region or a certain conductive structure in comparison to another response signal. In one embodiment, the processing circuitry is configured, for deriving said information indicative of a stimulation effectiveness of said electrical stimulation signal, to evaluate based on at least one of the at least two electrical response signals whether a left ventricular activity is identifiable in response to the electrical stimulation signal. The left ventricular activity may result from a left bundle branch area pacing, that is the coupling of the electrical stimulation signal to the left bundle branch. In another embodiment the left ventricular activity may result from a left ventricular stimulation using a left ventricular electrode lead extending into the left ventricle.

[0033] In one embodiment, the processing circuitry is configured to measure, repeatedly, at least two electrical response signals in response to the outputting of an electrical stimulation signal in a capture threshold test.

[0034] Within a capture threshold test, that stimulation energy shall be determined which reliably results in a desired capture and hence a desired stimulated cardiac activity. Within a capture threshold test, stimulation signals may for example be repeatedly generated and output, wherein the energy of the stimulation signals may for example be progressively reduced starting from a maximum starting energy, until a capture loss is identified. The signal energy at which (for the first time) a capture loss is observed corresponds to the capture threshold above which it is assumed that a reliable capture may be obtained, such that, during subsequent operation, the signal energy of the stimulation signal may be set to a value above the threshold.

[0035] In one embodiment, the processing circuitry is configured, for conducting a capture threshold test, to repeatedly measure at least two electrical response signals indicative of a stimulated cardiac activity in response to an electrical stimulation signal using at least two different pairs of electrode poles out of said at least three electrode poles and to derive information indicative of a stimulation effectiveness of said electrical stimulation signal based on said at least two electrical response signals. Within the capture threshold test, hence, repeated measurements of response signals are carried out, wherein for each electrical stimulation signal at least two electrical response signals are recorded and assessed. By assessing the at least two electrical response signals, it in particular may be evaluated whether the electrical stimulation signal results in a capture of a desired type, such that it not only is assessed whether a capture is obtained at all, but it also is assessed whether the capture corresponds to a desired stimulation.

[0036] For example, if within the context of a left bundle branch area pacing a left ventricular stimulation via the left bundle branch is desired, by assessing the at least two electrical response signals it may be determined whether a capture at the left bundle branch is obtained. Only if this is the case the capture is assumed to be effective, such that within the threshold test a signal energy is determined such that a desired capture is reliably obtained.

[0037] Within the capture threshold test it hence is not only distinguished between an effective stimulation (resulting in any stimulated activity whatsoever) and a non-effective stimulation, but it may be distinguished between a desired capture corresponding to an effective stimulation of a desired conductive structure, e.g. the left bundle branch, and a capture which does not include a stimulation of the desired conductive structure, e.g. the left bundle branch.

[0038] The capture threshold test may be automatically conducted by the implantable medical device prior to operation, e.g. in an initial calibration phase upon initial implantation, and / or repeatedly during operation, for example once or multiple times per day.

[0039] Within the capture threshold test, the energy of the electrical stimulation signal may be set such that during subsequent operation a reliable stimulation is obtained. For example, in one embodiment the processing circuitry is configured to adapt a signal strength of a current electrical stimulation signal with respect to a prior electrical stimulation signal during the capture threshold test based on information indicative of a stimulation effectiveness of the prior electrical stimulation signal. By repeating such measurements, for example starting from a maximum starting energy and by progressively reducing the signal energy until a non-effective stimulation of a desired structure is detected, a capture threshold is determined and the signal energy for subsequent operation may be set to a value above the threshold.

[0040] For example, during the capture threshold test it may be observed whether for a current stimulation signal a capture of a desired type is obtained. If this is the case, the signal energy is further reduced, until no effective stimulation of a desired, particular cardiac structure is observed, upon which the threshold is identified and the signal energy for subsequent operation may be set to a value above the threshold.

[0041] The assessment of a stimulation effectiveness may also be employed during regular operation, outside of a capture threshold test. For example, based on measuring at least two electrical response signals using different pairs of electrode poles in response to an electrical stimulation signal, it may be assessed whether during operation a desired stimulation in response to an electrical stimulation signal is obtained during a cardiac cycle, for example a left bundle branch stimulation. If, according to the at least two electrical response signals, it is determined that the desired structure (for example the left bundle branch) is not effectively stimulated, a backup pulse of a higher stimulation energy may be output.

[0042] By repeatedly observing the effectiveness of a stimulation, the signal energy of a stimulation pulse may be adaptively changed and hence automatically adapted during operation.

[0043] The electrical stimulation signal may have the shape of an electrical stimulation pulse. Such pulse may have one or multiple pulse phases of positive and / or negative amplitudes.

[0044] The different pairs of electrode poles may also be used for outputting electrical stimulation signals for causing a stimulation action, for example to cause a spatially differentiated stimulation of cardiac structures, for example to cause a left bundle branch pacing as well as a stimulation of the cardiac septum and hence a right ventricular stimulation.

[0045] During operation, in case a capture loss is detected, the processing circuitry may be configured to switch between different pairs of electrode poles for outputting electrical stimulation signals, such that in case of a capture loss it may be switched automatically from one stimulation polarity to another.

[0046] Alternatively or in addition, the processing circuitry may be configured to generate and output electrical stimulation signals using different stimulation vectors spanned by different pairs of electrode poles. In response to a particular stimulation signal at least two electrical response signals may be measured and may be assessed in order to evaluate an obtained capture. As a result, that stimulation vector may be used during operation which results in the optimum capture, e.g. that stimulation vector resulting in the narrowest QRS complex indicative of a most effective capture.

[0047] The implantable medical device may be a one-chamber IPG device.

[0048] The implantable medical device may be a two-chamber IPG device.

[0049] The implantable medical device may be a one-chamber ICD device.

[0050] The implantable medical device may be a two-chamber ICD device.

[0051] The implantable medical device may be a CRT device (CRT-P or CRT-D).

[0052] In another aspect, a method for operating an implantable medical device for performing a cardiac stimulation comprises: processing electrical signals using a processing circuitry of a generator device of the implantable medical device, wherein an electrode lead is connected to the generator device and extends from the generator device, the electrode lead comprising a lead body forming a distal end to be arranged on cardiac tissue within a patient’s heart; generating, using the processing circuitry, an electrical stimulation signal and providing the electrical stimulation signal to an electrode pole arrangement for stimulating cardiac activity, the electrode pole arrangement comprising at least three electrode poles; measuring, using the processing circuitry, at least two electrical response signals indicative of a stimulated cardiac activity in response to said electrical stimulation signal using at least two different pairs of electrode poles out of said at least three electrode poles; and deriving information indicative of a stimulation effectiveness of said electrical stimulation signal based on said at least two electrical response signals.

[0053] The advantages and advantageous embodiments described above for the implantable medical device equally apply also to the method, such that it shall be referred to the above in this respect. The idea of the invention shall subsequently be described in more detail with reference to the embodiments shown in the figures. Herein:

[0054] Fig. 1 shows a schematic view of an implantable medical device having a generator device and electrode leads;

[0055] Fig. 2 shows a schematic drawing of a distal end of an electrode lead in an implanted state;

[0056] Fig. 3 shows a schematic drawing of signal vectors spanned by different pairs of electrode poles of an electrode pole arrangement of the implantable medical device;

[0057] Fig. 4A shows the electrode pole arrangement of Fig. 3 spanning different signal vectors, illustrating a stimulation of the conductive structures of a right bundle branch and a left bundle branch;

[0058] Fig. 4B shows curves of response signals as measured using the different signal vectors in the stimulation scenario of Fig. 4A;

[0059] Fig. 5A shows the electrode pole arrangement of Fig. 3 spanning different signal vectors, illustrating a stimulation of the conductive structure of only the right bundle branch;

[0060] Fig. 5B shows curves of response signals as measured using the different signal vectors in the stimulation scenario of Fig. 5 A;

[0061] Fig. 6A shows the electrode pole arrangement of Fig. 3 spanning different signal vectors, illustrating a stimulation of the conductive structure of only the left bundle branch; Fig. 6B shows curves of response signals as measured using the different signal reception vectors in the stimulation scenario of Fig. 6A; and

[0062] Fig. 7 shows an example of an electrical response signal as measured using a certain pair of electrode poles, indicating characteristic metrics that may be derived from the electrical response signal for deriving information indicative of a stimulation effectiveness.

[0063] 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.

[0064] It is to be noted that the embodiments are not limiting for the invention, but merely represent illustrative examples.

[0065] 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 implantable medical device 1 is implanted in a patient, the implantable medical device 1 comprising a generator 12 connected to leads 10, 11 extending from the generator 12 through the superior vena V 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 potentially at different locations within the heart, and sense signals may be received.

[0066] In the embodiment of Fig. 1, an electrode lead 10 is implanted into the heart H such that it extends into the right ventricle RV of the heart H and, at a distal end 101 of a lead body 100, is arranged on intra-cardiac tissue at the septum M in between the right ventricle RV and the left ventricle LV of the heart H. An electrode lead 11 in turn is implanted such that it reaches into the right atrium RA.

[0067] An implantable medical 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 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 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.

[0068] Referring now to Fig. 2, the implantable medical device 1 as described herein in particular shall serve to provide a so-called left bundle branch area pacing, in short LBBAP. For this, the electrode lead 10 is implanted such that the lead body 100, with the distal end 101, is placed on tissue on the septum M such that it engages with tissue and reaches into tissue in order to couple to the left bundle branch LBB which, as part of the conductive structure of the patient’s heart H, is coupled via the so-called His bundle HIS to the atrioventricular node AVN and runs in parallel to the right bundle branch RBB. The left bundle branch LBB extends within myocardial tissue around the vertex of the left ventricle LV and conducts excitation signals for exciting tissue in the region of the left ventricle LV.

[0069] In the shown embodiment, the electrode lead 10 comprises an electrode pole 102 which is arranged on and protrudes from the distal end 101 of the lead body 100. The electrode pole 102 is formed by a helical spiral and is shaped such that it may be screwed into tissue in order to electrically couple to tissue and provide for a mechanical anchoring of the electrode lead 10 on tissue.

[0070] In addition, the electrode lead 10 comprises another electrode pole 103 which is formed by a ring electrode arranged proximally with respect to the electrode pole 102 on the lead body 100 of the electrode lead 10.

[0071] In an implanted state, as shown in Fig. 2, the electrode pole 102 formed by the helical spiral is engaged with tissue and reaches into tissue such that it electrically couples to the conductive structure within the myocardial tissue of the septum M, in particular the left bundle branch LBB, in order to enable a stimulation of the conductive structure by coupling stimulation signals to the conductive structure. At the same time, the electrode pole 103 may electrically contact tissue in that it fully or at least partially rests within tissue and hence electrically couples to tissue. During implantation, the electrode lead 10 is inserted, from the region of the right ventricle RV, into tissue such that the electrode pole 102 at the distal end 101 reaches a sufficient insertion depth within the tissue in order to couple to a desired conductive structure. In addition, also the electrode pole 103 shall establish a desired coupling to tissue.

[0072] During operation, by means of the electrode pole arrangement including the electrode poles 102, 103, electrical stimulation signals shall be output to couple into tissue in particular in the region of the left bundle branch LBB, as shown in Fig. 2, such that a spatially differentiated stimulation of the conductive structure of the left bundle branch LBB is obtained, causing a stimulated left ventricular activity, for example in the context of a cardiac resynchronization therapy (CRT).

[0073] During operation it is desirous to use electrical stimulation signals, in particular electrical stimulation pulses having one or multiple phases, exhibiting a signal energy which is sufficient to cause a reliable stimulation of a desired structure, in particular the left bundle branch LBB for a left bundle branch area pacing (LBBAP), while avoiding an excessive load of the electrical energy resources of the implantable medical device 1. For this, typically a capture threshold test is carried out at the initial startup of the implantable medical device 1 and repeatedly during operation, for example once or multiple times per day, in order to assess and set a signal strength for an electrical stimulation signal to cause a reliable stimulation of a desired structure.

[0074] For example, during a capture threshold test electrical stimulation signals are generated and output starting at a maximum start energy, wherein the signal energy is progressively reduced until a capture loss is detected. The signal energy at the capture loss is identified as a capture threshold. The signal energy for the electrical stimulation signal during subsequent operation is then set to a value above the threshold in order to obtain a reliable capture of a desired structure.

[0075] As, in the example of Fig. 2, a spatially dedicated stimulation of a certain conductive structure, namely the left bundle branch LBB, shall be established, it is desired to evaluate during the capture threshold test whether a capture of the desired structure is obtained, in comparison to just any capture resulting in any cardiac activity, for example a stimulation of the right bundle branch RBB only.

[0076] In general, it can be assumed that, if only the right bundle branch RBB is stimulated (in case of a disruption of the intrinsic cardiac conduction system, such as a left bundle branch block), a ventricular contraction is substantially prolonged and starts with a moderate mechanic contraction gradient caused by the contraction of the right ventricle, wherein only with a substantial time delay a contraction of also the left ventricle is observed. If the left bundle branch LBB is stimulated synchronously with the right bundle branch RBB, generally the ventricular contraction is significantly shortened and will exhibit a steeper mechanical contraction gradient, such that it is desirous to synchronously stimulate the left bundle branch LBB in case of e.g. a left bundle branch block to achieve synchronicity of the ventricular contractions.

[0077] Referring now to Fig. 3, the different electrode poles 102, 103 of the electrode lead 10 together with an electrode pole 121 formed by the housing of the generator device 12 span different signal vectors A, B, C, which may be used both for stimulation and for signal reception. Namely, the electrode pole 102 formed by the helical screw on the distal end 101 of the electrode lead 10 together with the electrode pole 121 of the generator device 12 forms a signal vector B. The electrode pole 103 arranged proximally with respect to the first electrode pole 102 on the electrode lead 10 forms a signal vector A together with the electrode pole 121 of the generator device 12. The electrode pole 102 and the electrode pole 103 together form a signal reception vector C.

[0078] In an implanted state, the electrode pole 102 formed by the helical screw on the distal end 101 of the electrode lead 10 shall couple to the conductive structure of the left bundle branch LBB and hence shall be placed in close proximity to the left bundle branch LBB. By means of the signal vector B, hence, a stimulation predominantly at the left bundle branch LBB and, in turn, a signal reception predominantly at the left bundle branch LBB may be achieved. The electrode pole 103, in comparison, is placed close to the conductive structure of the right bundle branch RBB, such that the signal vector A may be used predominantly for a signal stimulation and / or signal reception at the right bundle branch RBB.

[0079] The signal vector C between the electrode poles 102, 103 on the electrode lead 10 spans across the conductive structures of the right bundle branch RBB and the left bundle branch LBB, such that by means of the signal vector C a (non-selective) stimulation at both the left bundle branch LBB and the right bundle branch RBB may be obtained, and signals indicative of a difference in electrical potential and hence a difference in stimulation at the left bundle branch LBB and the right bundle branch RBB may be received.

[0080] During operation, stimulation signals may be output using a particular signal vector A, B, C or using multiple signal vectors A, B, C in combination, for example by using one (or both) of the electrode poles 102, 103 as a cathode and the electrode pole 121 of the generator device 12 as an anode.

[0081] In order to assess a stimulation effectiveness of a stimulation signal, response signals may be measured using different pairs of electrode poles 102, 13, 1021 spanning different signal vectors A, B, C, such that response signals are obtained carrying spatially differentiated information relating to a stimulation of certain regions and structures.

[0082] Referring now to Figs. 4A and 4B, by outputting a stimulation signal in the shape of a stimulation pulse using for example the pair of electrode poles 102, 103 spanning the signal vector C, the conductive structures of both the left bundle branch LBB and the right bundle branch RBB may be stimulated, as illustrated by the stars in Fig. 4A. Correspondingly, when measuring response signals using the different signal vectors A, B, C spanned by the different pairs of electrode poles 102, 103, 121, response signals SA, SB, SC as illustrated in Fig. 4B are obtained. Herein, due to the (approximately) synchronous excitation of the conductive structures of the left bundle branch LBB and right bundle branch RBB the response signals SA, SB associated with the signal vectors A, B indicate a substantial signal level, whereas the response signal SC is of substantially smaller magnitude, as the difference between the stimulation responses in the conductive structures of the left bundle branch LBB and the right bundle branch RBB is comparatively small.

[0083] Referring now to Figs. 5A, 5B, if the stimulation signal yields an effective stimulation only of the conductive structure of the right bundle branch RBB, as illustrated by the stars in Fig. 5 A, the response signal SA associated with the signal vector A may exhibit a substantial signal level, whereas the response signal SB associated with the signal vector B does not, as apparent from Fig. 5B. As the difference between the response signals SA, SB is large, also the response signal SC associated with the signal vector C exhibits a comparatively large signal level, due to the difference in electrical potential of the stimulation responses of the left bundle branch LBB and the right bundle branch RBB.

[0084] Referring now to Figs. 6A, 6B, if the stimulation signal causes a stimulation only of the conductive structure of the left bundle branch LBB, as indicated by the stars in Fig. 6A, the response signal SB associated with the signal vector B is strong, as apparent from Fig. 6B, whereas the response signal SA associated with the signal vector A is comparatively small. Again, as in the example of Figs. 5 A, 5B, the response signal SC of the signal vector C is comparatively large, due to the difference in the stimulation responses of the left bundle branch LBB and the right bundle branch RBB.

[0085] As it is apparent from the examples of Figs. 4A, 4B, 5A, 5B and 6A, 6B, by putting the different response signals SA, SB, SC into relation with one another, it may be determined which conductive structure is effectively stimulated by a stimulation signal.

[0086] It hence may be determined whether a stimulation signal yields a capture, that is an effective stimulation, extending to a particular conductive structure, such as the left bundle branch LBB, or not.

[0087] To put the response signals SA, SB, SC into relation with one another, for example characteristic measures may be determined for each response signal SA, SB, SC. Referring now to Fig. 7, each response signal SA, SB, SC - in Fig. 7 referred to simply as response signal S - is measured at a defined time distance TW with respect to a prior stimulation signal P, the timing distance TW for example corresponding to a blanking window in a measurement channel following the output of the stimulation signal P during a cardiac cycle. The response signal S herein is measured over a defined time period TM using a particular pair of electrode poles 102, 103, 121.

[0088] According to the measured response signal S, characteristic metrics values may be determined, for example maximum and minimum amplitude values Ml, M2, temporal locations XI, X2, X3 relating to zero-crossings, threshold-crossings or maximum or minimum amplitude values, time durations Tl, T2 of certain signal portions, for example relating to a positive signal portion and a negative signal portion, or area values Al, A2 indicative of the area under certain portions of the signal curve. The metrics value may in particular be useful to evaluate a signal level (signal energy) of an overall response signal or certain portions of a response signal.

[0089] The different response signals SA, SB, SC may be compared according to the characteristic metrics, such that for example an effective signal level of one response signal in comparison to another response signal may be assessed.

[0090] By putting the different response signals SA, SB, SC obtained by using the different pairs of electrode poles 102, 103, 121 spanning different signal vectors A, B, C into relation with one another, information is derived indicating whether a desired capture is achieved by means of the stimulation signal, i.e., a stimulation of a particular kind, in particular a stimulation of a certain region or structure, such as the left bundle branch LBB.

[0091] The assessment of a capture may in particular be useful in a capture threshold test in which, during the initial startup of the implantable medical device 1 or repeatedly during operation, a capture threshold is determined indicative of a signal energy below which a capture loss is to be expected. During a capture threshold test, electrical stimulation signals may be repeatedly generated, starting from a maximum signal energy and progressively reducing the signal energy of the electrical stimulation signal. In response to each electrical stimulation signal, electrical response signals SA, SB, SC are measured using different pairs of electrode poles 102, 103, 121, such that for each electrical stimulation signal it is assessed whether a desired stimulation is effectively achieved, in particular a stimulation of the left bundle branch LBB. If it is found that for a current stimulation signal at a particular stimulation energy a desired stimulation is achieved, another stimulation signal is generated at a reduced signal energy, until it is found that the desired capture is no longer achieved, for example because the left bundle branch LBB no longer is stimulated by the stimulation signal, as indicated by the combination of response signals SA, SB, SC.

[0092] In particular, by putting the response signals SA, SB, SC, as illustrated in Figs. 4A, 4B, 5A, 5B and 6A, 6B, into relation with one another, it may be concluded whether a stimulation signal yields a selective left bundle branch area pacing (LBBAP, i.e., a stimulation of only the left bundle branch LBB), a non-selective LBBAP (i.e., a stimulation of both the left bundle branch LBB and the right bundle branch RBB and / or the septum), a right bundle branch area pacing (RBBAP, i.e., a stimulation of only the right bundle branch RBB and / or the septum), or a no capture. During the capture threshold test it hence may be assessed whether a particular stimulation is achieved, and the capture threshold may be set accordingly. During subsequent operation the signal level of the stimulation pulse is then set to a value above the capture threshold, such that an effective, reliable stimulation during operation can be expected.

[0093] The idea underlying the invention is not limited to the embodiments described above, but may be implemented in an entirely different fashion.

[0094] An electrode pole arrangement of an implantable medical device may comprise three or more electrode poles arranged on one or more electrode leads and on the housing of the generator device. An implantable medical device may be configured for providing for a left bundle branch area pacing, but may, alternatively or in addition, implement different pacing functions.

[0095] List of Reference Numerals

[0096] I Implantable medical stimulation device

[0097] 10 Lead

[0098] 100 Lead body

[0099] 101 Distal end

[0100] 102 Electrode pole

[0101] 103 Electrode pole

[0102] I I Lead

[0103] 12 Generator

[0104] 120 Processing circuitry

[0105] 121 Housing

[0106] Al, A2 Area

[0107] AVN Atrioventricular node

[0108] H Heart

[0109] HIS HIS bundle branch

[0110] LA Left atrium

[0111] LBB Left bundle branch

[0112] LV Left ventricle

[0113] M Intra-cardiac tissue (myocardium)

[0114] Ml, M2 Amplitude

[0115] P Stimulation signal (pacing signal)

[0116] RA Right atrium

[0117] RBB Right bundle branch

[0118] RV Right ventricle

[0119] S, SA, SB, SC Response signal t Zeit

[0120] Tl, T2 Duration

[0121] V Superior vena

[0122] X1-X3 Temporal location

Claims

Claims1. An implantable medical device (1) for performing a cardiac stimulation, the implantable medical device (1) comprising: a generator device (12) comprising a processing circuitry (120) for processing electrical signals, an electrode lead (10, 11) connected to the generator device (12) and extending from the generator device (12), the electrode lead (10) comprising a lead body (100) forming a distal end (101) to be arranged on cardiac tissue within a patient’s heart (H), and an electrode pole arrangement comprising at least three electrode poles (102, 103, 121), wherein the processing circuitry (120) is configured to generate an electrical stimulation signal (P) and to provide the electrical stimulation signal (P) to said electrode pole arrangement for stimulating cardiac activity, characterized in that the processing circuitry (120) is configured to measure at least two electrical response signals (S, SA, SB, SC) indicative of a stimulated cardiac activity in response to said electrical stimulation signal (P) using at least two different pairs of electrode poles out of said at least three electrode poles (102, 103, 121) and to derive information indicative of a stimulation effectiveness of said electrical stimulation signal (P) based on said at least two electrical response signals (S, SA, SB, SC).

2. The implantable medical device (1) according to claim 1, characterized in that a first of the at least three electrode poles (102, 103, 121) is arranged on the distal end (101) of the lead body (100) and is configured to be inserted into cardiac tissue.

3. The implantable medical device (1) according to claim 2, characterized in that the first of the at least three electrode poles (102, 103, 121) is configured to be inserted into cardiac tissue to operatively engage with a conductive structure of the left bundle branch (LBB) in intra-cardiac tissue (M).

4. The implantable medical device (1) according to claim 2 or 3, characterized in that a second of the at least three electrode poles (102, 103, 121) is arranged on the lead body (100) at a location proximal to the first of the at least three electrode poles (102, 103, 121), and a third of the at least three electrode poles (102, 103, 121) is arranged on the generator device (12).

5. The implantable medical device (1) according to claim 4, characterized in that a first pair of electrode poles is formed by the first of the at least three electrode poles (102, 103, 121) and the third of the at least three electrode poles (102, 103, 121), and a second pair of electrode poles is formed by the second of the at least three electrode poles (102, 103, 121) and the third of the at least three electrode poles (102, 103, 121), wherein the processing circuitry (120) is configured to measure a first electrical response signal (SB) using the first pair and a second electrical response signal (SA) using the second pair.

6. The implantable medical device (1) according to claim 4 or 5, characterized in that a third pair of electrode poles is formed by the first of the at least three electrode poles (102, 103, 121) and the second of the at least three electrode poles (102, 103, 121), wherein the processing circuitry (120) is configured to measure a third electrical response signal (SC) using the third pair.

7. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (120) is configured to measure said at least two electrical response signals (S, SA, SB, SC) at a defined timing distance (TW) with respect to said electrical stimulation signal (P).

8. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (120) is configured to evaluate, for deriving said information indicative of a stimulation effectiveness of said electrical stimulation signal (P), for at least one of the at least two electrical response signals (S, SA, SB, SC) at least one of a maximum or minimum amplitude value (Ml, M2), a temporal location (XI -X3) of a zero-crossing or a maximum or minimum amplitude(Ml, M2), an area (Al, A2) under a curve of the respective electrical response signal, a signal width (Tl, T2) of a defined portion of the respective electrical response signal, and a derivative value.

9. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (120) is configured to compare at least one of the at least two electrical response signals (S, SA, SB, SC) to a reference curve and to derive said information indicative of a stimulation effectiveness of said electrical stimulation signal (P) based on the comparison.

10. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (120) is configured to compare the at least two electrical response signals (S, SA, SB, SC) to each other and to derive said information indicative of a stimulation effectiveness of said electrical stimulation signal (P) based on the comparison.

11. The implantable medical device (1) according to one of one of the preceding claims, characterized in that the processing circuitry (120) is configured, for deriving said information indicative of a stimulation effectiveness of said electrical stimulation signal (P), to evaluate based on at least one of the at least two electrical response signals (S, SA, SB, SC) whether left ventricular activity is identifiable in response to said electrical stimulation signal (P).

12. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (120) is configured, for conducting a capture threshold test, to repeatedly measure at least two electrical response signals (S, SA, SB, SC) indicative of a stimulated cardiac activity in response to an electrical stimulation signal (P) using at least two different pairs of electrode poles out of said at least three electrode poles (102, 103, 121) and to derive information indicative of a stimulation effectiveness of said electrical stimulation signal (P) based on said at least two electrical response signals (S, SA, SB, SC).

13. The implantable medical device (1) according to claim 12, characterized in that the processing circuitry (120) is configured to adapt a signal strength of a current electrical stimulation signal (P) with respect to a prior electrical stimulation signal (P) during said capture threshold test based on information indicative of a stimulation effectiveness of said prior electrical stimulation signal (P).

14. The implantable medical device (1) according to claim 12 or 13, characterized in that the processing circuitry (120) is configured to determine a capture threshold as a result of the capture threshold test.

15. A method for operating an implantable medical device (1) for performing a cardiac stimulation, the method comprising: processing electrical signals using a processing circuitry (120) of a generator device (12) of the implantable medical device (1), wherein an electrode lead (10, 11) is connected to the generator device (12) and extends from the generator device (12), the electrode lead (10) comprising a lead body (100) forming a distal end (101) to be arranged on cardiac tissue within a patient’s heart (H), generating, using the processing circuitry (120), an electrical stimulation signal (P) and providing the electrical stimulation signal (P) to an electrode pole arrangement for stimulating cardiac activity, the electrode pole arrangement comprising at least three electrode poles (102, 103, 121), characterized by measuring, using the processing circuitry (120), at least two electrical response signals (S, SA, SB, SC) indicative of a stimulated cardiac activity in response to said electrical stimulation signal (P) using at least two different pairs of electrode poles out of said at least three electrode poles (102, 103, 121), and deriving information indicative of a stimulation effectiveness of said electrical stimulation signal (P) based on said at least two electrical response signals (S, SA, SB, SC).

Images