Implantable medical device comprising an electrode pole arrangement

Abstract

An implantable medical device (1) comprises an electrode pole arrangement (113-115) for sensing electrical signals, and a processing circuitry (102) for processing a sensed signal (S) obtained using the electrode pole arrangement (113-115). The processing circuitry (102) is configured to obtain first signal samples (Si) indicative of the sensed signal (S) at a first sampling rate, derive, based on the first signal samples (Si), second signal samples (Sk) at a second sampling rate, identify, based on the sensed signal (S), an event (E) and generate, for said event (E), an event marker (M1-M3) in association with an associated second signal sample, and communicate information indicative of said second signal samples (Sk) and said event marker (M1-M3) to an external device (2). The processing circuitry (102) is further configured to determine, for said event marker (M1-M3), timing information (TI) indicative of a relative timing (D1*, D1**) of said event marker (M1-M3).

Description

[0001] Applicant: BIOTRONIK SE & Co. KG

[0002] Implantable medical device comprising an electrode pole arrangement

[0003] The invention concerns an implantable medical device according to the preamble of claim 1 and a method for storing electrical signal data according to the preamble of claim 14.

[0004] An implantable medical device of this kind comprises an electrode pole arrangement for sensing electrical signals. A processing circuitry for processing a sensed signal obtained using the electrode pole arrangement is configured to obtain first signal samples indicative of the sensed signal at a first sampling rate and to derive, based on the first signal samples, second signal samples at a second sampling rate smaller than the first sampling rate, each second signal sample being associated with a time span encompassing a multiplicity of first signal samples. The processing circuitry furthermore is configured to identify, based on the sensed signal, an event and to generate, for said event, an event marker in association with an associated second signal sample. In addition, the processing circuitry is configured to store information indicative of the second signal samples and the event marker in a memory unit of the implantable medical device for further processing or for communication to an external device.

[0005] An implantable medical device of the type concerned herein may be for example a cardiac stimulation device, such as a cardiac pacemaker device or a cardiac defibrillation device. In some embodiments, the implantable medical device may be an IPG device, an ICD device or a CRT device, such as a CRT-D or CRT-P device. In other embodiments, the implantable medical device may be a cardiac monitoring device or an implantable sensor device. The implantable medical device is generally configured to sense electrical signals, such as electrocardiogram signals, using an electrode pole arrangement comprising two or more electrode poles spanning one or multiple signal reception vectors.

[0006] Implantable medical devices, such as cardiac stimulation devices, are generally designed to operate in an implanted state in a patient over a prolonged duration of time. Hence, due to size restrictions of implantable medical devices, also battery and memory capacities are naturally limited, such that implantable medical devices are required to operate in an energy and memory efficient manner.

[0007] This also relates to the communication with an external device. In order to ensure an energy efficient and reliable communication, information relating to sensed signals is compressed and is transmitted to the external device at a reduced sampling rate. For example, first signal samples indicative of a sensed signal may be obtained at a first sampling rate of e.g. 512 Hz and may be processed internally in the implantable medical device at the first sampling rate, but are then reduced to a second sampling rate, for example 128 Hz, to obtain second signal samples at the second sampling rate for transmission to the external device.

[0008] During the processing of sensed signals in an implantable medical device, certain events shall be identified, such as contraction events, which may be identified e.g. according to the R peak in a QRS wave form in an electrocardiogram signal or according to the crossing of a predefined threshold or the like. Based on identified events, for example ventricular intrinsic or paced contraction events or atrial intrinsic or paced contraction events or bradycardia or tachycardia events, for example a stimulation operation may be controlled.

[0009] Events may be identified by the processing circuitry based on the sensed signal, for example at the internal first sampling rate. If information regarding an event marker indicative of an identified event is then transmitted to the external device in association with the second signal samples at the second sampling rate, the external device may associate the event marker only with the sampling time of an associated second signal sample, which however may be to some extent inaccurate, as the second sampling rate may be substantially smaller than the first sampling rate at which the internal processing within the implantable medical device takes place.

[0010] On the other hand, adjusting the second sampling rate to a desired temporal resolution of events would be rather inefficient, since, in general, a number of events is still small compared to a number of second signal samples in a time interval.

[0011] It is an object of the instant invention to provide an implantable medical device and a method for storing electrical signal data in the implantable medical device which allow for a storage of more accurate information e.g. on heart signals and stimulation events sensed by the implantable medical device in a storage space saving manner. Moreover, the present invention allows for providing more accurate information to be further processed by the implantable medical device at a later point in time or to be transmitted by the implantable medical device to an external device in a general resources-saving manner.

[0012] These objects are achieved by means of an implantable medical device comprising the features of claim 1 and a method comprising the features of claim 14.

[0013] Accordingly, the processing circuitry is further configured to determine, for said event marker, timing information indicative of a relative timing of said event marker within said time span of the associated second signal sample and to store said timing information in the memory unit.

[0014] Using the processing circuitry of the implantable medical device, one or multiple events are identified based on one or multiple sensed signals obtained using the electrode pole arrangement of the implantable medical device. For each event, an event marker is generated, and information indicative of the event marker is stored in the memory unit.

[0015] As, for storing in the memory unit, the sensed signal is reduced (compressed) to second signal samples at a second sampling rate and, for storing in the memory unit, each event is associated with a second signal sample into whose time span the event falls, the resolution of timing information for the event marker is generally limited to the temporal resolution of the associated second signal sample, which corresponds to the second sampling rate. For example, if the second sampling rate is at 128 Hz, the time period between successive second signal samples is of about 7.8 ms. Thus, if each event is associated with the sampling time of an associated second signal sample, the temporal resolution of the corresponding event marker is to some extent inaccurate, due to the limited temporal resolution of the second signal samples.

[0016] In order to be able to analyze and display stored marker information with an improved timing accuracy, it herein is proposed to determine, for an event marker, timing information indicative of a relative timing of the event marker within the time span of the associated second signal sample and to store the timing information in the memory unit such that the event marker can be associated with a more accurate timing information and correspondingly processed.

[0017] Generally, each second signal sample is associated with a time span, the time span corresponding for example to the time period between successive second signal samples. From first signal samples within a particular time span, a corresponding second signal sample is derived, for example by averaging or by in another way combining or selecting from the first signal samples within the time span. As additional timing information for an event marker is stored indicating a relative timing of the event marker within the time span, not only information about the occurrence of the event marker (anywhere) in the time span preserved, but also information about a timing of the event marker within time span is preserved. Hence the timing of the event marker within the time span can be analyzed in later processing of the data, and stored second signal samples and the stored event marker information can be processed correspondingly.

[0018] The implantable medical device in particular may be a cardiac device, in particular a cardiac stimulation device, such as a cardiac pacemaker device or a cardiac defibrillation device, for example an IPG device, an ICD device, a CRT-D device or a CRT-P device. Electrical signals sensed using the electrode pole arrangement of the implantable medical device hence beneficially are electrocardiogram signals.

[0019] In other embodiments the implantable medical device may be a monitoring device, a sensor device, or a neuro-stimulation device.

[0020] The implantable medical device may for example be a cardiac device comprising leads on which electrode poles forming the electrode pole arrangement are placed. In other embodiments, the implantable medical device may be a leadless device not comprising leads, but carrying electrode poles for example on a housing, which is designed for an immediate implantation into the patient's heart.

[0021] The information stored in the memory unit as described above may then be provided for further processing or for transmission to an external device, such as an external communication device, for example a smart phone, a tablet computer or another communication device for example in the context of a home monitoring system, or an external programming device.

[0022] In one embodiment, the first sampling rate is an integer multiple of the second sampling rate.

[0023] For example, the first sampling rate may he in a range between 64 Hz and 2048 Hz. The second sampling rate for example may lie in a range between 32 Hz and 1024 Hz. In one example, the first sample rate may be 512 Hz. The second sampling rate may for example be 128 Hz. The first sampling rate is hence an integer multiple of 4 of the second sampling rate.

[0024] In one embodiment, the processing circuitry is configured to derive a sample value of each of the second signal samples according to a maximum value of first signal samples in the time span associated with the second signal sample.

[0025] Generally, the second signal sample is determined according to the first signal samples falling into the time span associated with the particular second signal sample. The value of the second signal sample herein may be determined by any suitable form of combining the values of the first signal samples within the time span, for example by averaging the first signal samples or by selecting one of the first signal samples. In one embodiment, the value of the second signal sample is determined according to the first signal sample having the largest value within the time span associated with the second signaling sample.

[0026] If the first sampling rate for example is at 512 Hz and the second sampling rate is at 128 Hz, four first signal samples fall into the time span associated with each second signal sample, such that the value of the second signal sample is chosen by combining or selecting from the first signal samples falling into the time span.

[0027] In one embodiment, the processing circuitry is configured to identify the event at a first sampling time of an associated first signal sample, wherein the timing information is indicative of a relative timing of the first sampling time in the time span of the associated second signal sample. The processing within the processing circuitry of the implantable medical device generally takes place at the first sampling rate. Accordingly, using the first signal samples at the first sampling rate an event is identified, for example according to a threshold crossing or according to a maximum value in a signal portion or the like. An event identified by the processing circuitry hence is associated with a first sampling time of an associated first signal sample, e.g. the first signal sample at which the threshold crossing has been detected. Herein, the additional timing information indicative of the timing of the event marker within the time span associated with the second signal sample indicates the relative timing in relation to the first sampling time of the first signal sample for which the event has been determined. The timing information hence yields a timing resolution of the event marker corresponding to the first sampling rate. In one embodiment, the relative timing is measured with respect to a second sampling time of the associated second signal sample or with respect to a third sampling time of a second signal sample prior to the associated second signal sample. The relative timing of the event marker within the time span in particular may be expressed with relation to the sampling time of the second signal sample that is associated with the time span. In another embodiment, the relative timing may be expressed by the relative time to the prior second signal sample.

[0028] By expressing the timing information associated with the event marker as a relative timing information with respect to the sampling time of a second signal sample, no absolute time stamp must be stored for the event marker. The relative timing information may be expressed in an efficient manner with a limited number of bits, thus saving storage space, while maintaining the temporal resolution of the first sampling rate for the event marker.

[0029] In one embodiment, the processing circuitry is configured to obtain the first signal samples at a first bit resolution and to code the second signal samples for storing in the memory unit at a second bit resolution smaller than the first bit resolution. To further compress the data to be stored in the memory unit, the first signal samples may be processed within the implantable medical device at an increased resolution, for example at a bit resolution in between 8 to 24 bit. When deriving the second signal samples for storing in the memory unit, however, the bit resolution can be reduced, such that the second signal samples have a bit resolution for example in a range between 6 to 16 bit and in any way smaller than the first bit resolution.

[0030] For example, the first signal samples may be processed internally within the processing circuitry of the implantable medical device at 10 bit, such that each first signal sample value is expressed by a 10 bit code word. The second signal samples, in contrast, have a bit resolution which is decreased with respect to the bit resolution of the first signal samples and may for example be at 7 bit. The second signal samples hence are not only obtained at a reduced sampling rate, but are also coded with a reduced bit resolution, such that each sampling value is expressed using a reduced number of bits.

[0031] In one embodiment, the processing circuitry is configured to code the timing information associated with the event marker using a code word comprising N bit, where 2N=Z and Z corresponds to the ratio of the first sampling rate to the second sampling rate. The timing information indicative of the relative timing of the event marker within the time span of the associated second signal sample is beneficially expressed based on the temporal resolution of the first signal samples. If, for example, the first sampling rate is 512 Hz and the second sampling rate is 128 Hz, the ratio between the first sampling rate and the second sampling rate is 4, such that four first signal samples fall into the time span associated with each second signal sample. The timing information, which shall indicate the relative timing of the event marker within the time span, hence may point to any of the sampling times of the four first signal samples falling into the time span associated with a particular second signal sample and hence may have 4 different values, such that two bit are sufficient to code the timing information. This follows from the equation 2N=Z, where Z is the ratio between the first sampling rate and the second sampling rate and N is the number of bit used for coding the timing information. If the ratio is Z=4, then N=2, such that two bit are sufficient to code the timing information indicative of the relative timing of the event marker within the time span. If Z=8, then N=3, such that three bit are required to code the timing information indicative of the relative timing of the event marker within the time span of the associated second signal sample.

[0032] In one embodiment, the implantable medical device comprises a generator device and at least one electrode lead connected to the generator device. The electrode pole arrangement comprises a multiplicity of electrode poles, at least one of which is arranged on the at least one electrode lead. The implantable medical device in particular may be a cardiac stimulation device comprising leads, wherein one or multiple leads may be implanted to reach into the patient's heart, or may be implanted such that they rest outside of the patient's heart (so-called non- transvenous implantable cardiac stimulation device).

[0033] In other embodiments, the implantable medical device may be a device not comprising leads. Electrode poles in this case are formed for example on a housing of the implantable medical device, for example by different housing sections of the implantable medical device. For example, the implantable medical device may be a leadless pacemaker designed for immediate implantation into the patient's heart.

[0034] In one embodiment, the processing circuitry is configured to derive, in a regular mode, the second signal samples at the second sampling rate and, in a mode of increased sampling resolution, at a third sampling rate larger than the second sampling rate and to store information indicative of the second signal samples in the memory unit. In one embodiment, the processing circuitry may be configured to switch between different modes of operation, namely the regular mode and the mode of increased sampling resolution. In the regular mode the processing circuitry determines second signal samples at the second sampling rate based on first signal samples at the first sampling rate. In particular, each second signal sample may be determined based on first signal samples falling into a time span associated with the particular second signal sample, by for example combining the first signal samples for example by averaging or by selecting in a suitable way from the first signal samples within the time span. Information relating to the second signal samples may then be stored in the memory unit. If the processing circuitry however switches to the mode of increased sampling resolution, the second signal samples are not obtained at the second sampling rate, but at a third sampling rate larger than the second sampling rate. In the mode of increased sampling resolution, hence, the sampling rate of the second signal samples is increased, such that information relating to signal samples are stored in the memory unit at an increased sampling resolution.

[0035] The third sampling rate in the mode of increased sampling resolution may for example be equal to the first sampling rate. In the mode of increased sampling resolution, hence, no sampling rate reduction takes place in comparison to the first sampling rate, which is used for internal processing within the processing circuitry.

[0036] In one embodiment, the processing circuitry is configured to switch, at a first switching time, from the regular mode to the mode of increased sampling resolution and, at a second switching time, from the mode of increased sampling resolution to the regular mode. The switching may for example be event-based. For example, the processing circuitry may be configured to switch to the mode of increased sampling resolution to cover a certain signal portion, for example relating to a QRS waveform, to a P wave or to a T wave, at the increased sampling resolution. The timing of switching may for example be determined based on prior interval lengths. Alternatively or in addition, the timing of switching may be determined based on identified signal features, such as a P wave peak, an R peak or the end of a T wave. Alternatively or in addition, the timing of switching may be determined based on a processing of an atrial channel. Alternatively or in addition, the timing of switching may be determined based on morphological criteria of a prior event, such as a prior QRS complex. A time period between the first switching time and the second switching time may in particular be shorter than a cardiac cycle length, for example equal to or shorter than 50 % of a cardiac cycle length.

[0037] By variably switching between different sampling rates, certain signal portions may be recorded with an increased sampling resolution. The third sampling rate herein may be fixed, for example programmed prior to operation. In other embodiments, the third sampling rate may be adaptive and may be variable during operation, depending for example on the type of signal feature which shall be covered by the increased sampling resolution.

[0038] In one embodiment, the processing circuitry is configured to generate, at the first switching time and / or at the second switching time, a switching event marker and to store information relating to the switching event marker in the memory unit. To indicate that the processing circuitry has switched to the mode of increased sampling resolution or back to the regular mode, switching event markers are also stored in the memory unit. By means of the switching event markers the switching between different modes is indicated in the stored data, such that the second signal samples can be processed at the particular sampling rate according to the mode at to which it has been switched.

[0039] In a second aspect, an implantable medical device comprises an electrode pole arrangement for sensing electrical signals, a processing circuitry for processing a sensed signal obtained using the electrode pole arrangement and a memory unit. The processing circuitry is configured to: obtain first signal samples indicative of the sensed signal at a first sampling rate derive, based on the first signal samples, second signal samples at a second sampling rate smaller than the first sampling rate, each second signal sample being associated with a time span encompassing a multiplicity of first signal samples, identify, based on the sensed signal, an event and generate, for said event, an event marker associated with an associated second signal sample, and store information indicative of said second signal samples and said event marker in the memory unit. The processing circuitry is further configured to derive, in a regular mode, said second signal samples at said second sampling rate and, in a mode of increased sampling resolution, at a third sampling rate larger than said second sampling rate and to store information indicative of said second signal samples at the third sampling rate in the memory unit. The stored data may be communicated to an external device for processing by the external device. In this way, electrical signal data may be transmitted in a resources-saving manner.

[0040] The advantages and advantageous embodiments as described above equally apply also to the implantable medical device of this aspect, such that it shall be referred to the above.

[0041] In particular, in relation to the second aspect, the processing circuitry may be configured to switch between different modes of operation, namely the regular mode and the mode of increased sampling resolution. In the regular mode the processing circuitry determines second signal samples at the second sampling rate based on first signal samples at the first sampling rate. In particular, each second signal sample may be determined based on first signal samples falling into a time span associated with the particular second signal sample, by for example combining the first signal samples for example by averaging or by selecting in a suitable way from the first signal samples within the time span. Information relating to the second signal samples may then be stored in the memory unit. If the processing circuitry however switches to the mode of increased sampling resolution, the second signal samples are not obtained at the second sampling rate, but at a third sampling rate larger than the second sampling rate. In the mode of increased sampling resolution, hence, the sampling rate of the second signal samples is increased, such that information relating to signal samples are stored in the memory unit at an increased sampling resolution.

[0042] The third sampling rate in the mode of increased sampling resolution may for example be equal to the first sampling rate. In the mode of increased sampling resolution, hence, no sampling rate reduction takes place in comparison to the first sampling rate, which may be used for internal processing within the processing circuitry.

[0043] In one embodiment, the processing circuitry is configured to switch, at a first switching time, from the regular mode to the mode of increased sampling resolution and, at a second switching time, from the mode of increased sampling resolution to the regular mode. The switching may for example be event-based. For example, the processing circuitry may be configured to switch to the mode of increased sampling resolution to cover a certain signal portion, for example relating to a QRS waveform, to a P wave or to a T wave, at the increased sampling resolution. The timing of switching may for example be determined based on prior interval lengths. Alternatively or in addition, the timing of switching may be determined based on identified signal features, such as a P wave peak, an R peak or the end of a T wave. Alternatively or in addition, the timing of switching may be determined based on a processing of an atrial channel. Alternatively or in addition, the timing of switching may be determined based on morphological criteria of a prior event, such as a prior QRS complex.

[0044] A time period between the first switching time and the second switching time may in particular be shorter than a cardiac cycle length, for example equal to or shorter than 50 % of a cardiac cycle length.

[0045] By variably switching between different sampling rates, certain signal portions may be recorded with an increased sampling resolution. The third sampling rate herein may be fixed, for example programmed prior to operation. In other embodiments, the third sampling rate may be adaptive and may be variable during operation, depending for example on the type of signal feature which shall be covered by the increased sampling resolution.

[0046] In one embodiment, the processing circuitry is configured to generate, at the first switching time and / or at the second switching time, a switching event marker and to store information relating to the switching event marker in the memory unit. To indicate in the stored data that the processing circuitry has switched to the mode of increased sampling resolution or back to the regular mode, switching event markers are also stored in the memory unit. By means of the switching event markers the switching between different modes is indicated in the stored data, such that the second signal samples can be processed at the particular sampling rate according to the mode at to which it has been switched.

[0047] In a third aspect, the present invention includes a method for storing electrical signal data in an implantable medical device according to the specification above. The method comprises the following steps: obtaining first signal samples indicative of the sensed signal at a first sampling rate, deriving, based on the first signal samples, second signal samples at a second sampling rate smaller than the first sampling rate, each second signal sample being associated with a time span encompassing a multiplicity of first signal samples, identifying, based on the sensed signal, an event and generate, for said event, an event marker in association with an associated second signal sample, and storing information indicative of said second signal samples and said event marker in the memory unit, determining, for said event marker, timing information indicative of a relative timing of said event marker within said time span of the associated second signal sample, and storing said timing information in the memory unit.

[0048] In a fourth aspect, the present invention relates to a method for storing electrical signal data in an implantable medical device according to the specification above, comprising the following steps: obtaining first signal samples indicative of the sensed signal at a first sampling rate, deriving, based on the first signal samples, second signal samples at a second sampling rate smaller than the first sampling rate, each second signal sample being associated with a time span encompassing a multiplicity of first signal samples, identifying, based on the sensed signal, an event and generate, for said event, an event marker in association with an associated second signal sample, and storing information indicative of said second signal samples and said event marker in the memory unit, deriving, in a regular mode, said second signal samples at said second sampling rate and, in a mode of increased sampling resolution, at a third sampling rate larger than said second sampling rate, and storing information indicative of said second signal samples in the memory unit. The idea of the invention shall subsequently be described in more detail with reference to the embodiments as shown in the drawings. Herein:

[0049] Fig. 1 shows a schematic drawing of an implantable medical device according to a first embodiment of the present invention in an implanted state in a patient;

[0050] Fig. 2 shows a schematic drawing of an implantable medical device according to a second embodiment of the present invention in an implanted state in a patient;

[0051] Fig. 3 shows the implantable medical device of Fig. 2, illustrating sense vectors spanned by different pairs of electrode poles of an electrode pole arrangement of the device;

[0052] Fig. 4 shows a schematic drawing of an implantable medical device according to a third embodiment of the present invention;

[0053] Fig. 5 shows a drawing of a sensed signal, indicating first and second signal samples derived from the sensed signal; Fig. 6 shows a schematic drawing of encoded information relating to second signal sample values, marker information and timestamps;

[0054] Fig. 7 shows a schematic drawing of a sensed signal, indicating first signal samples and second signal samples derived from the first signal samples;

[0055] Fig. 8 shows the schematic drawing of Fig. 7, indicating a potential inaccuracy originating from the temporal resolution of the second signal samples;

[0056] Fig. 9 shows the schematic drawing of Fig. 7, indicating an additional timing information for an event marker;

[0057] Fig. 10 shows the schematic drawing of Fig. 9, indicating a modified timing information for the event marker; and

[0058] Fig. 11 shows a schematic drawing of a switching between two modes for covering a signal portion with an increased sampling resolution.

[0059] 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.

[0060] It is to be noted that the embodiments are not limiting for the invention, but merely represent illustrative examples.

[0061] Fig. 1 shows an embodiment of an implantable medical device 1 according to the present invention, which in the shown, non-limiting embodiment of Fig. 1 is an implantable cardioverter defibrillator device designed as a transvenously implantable cardioverter defibrillator device.

[0062] The implantable medical device 1 in the embodiment of Fig. 1 comprises a generator device 10 encapsulated within a housing 100, and a lead 11 connected to the generator device 10 at a proximal end 111 and carrying electrode poles 113, 114 as well as a shock electrode 115 in the shape of a coil formed on a distal portion of the lead 11. The electrode lead 11 of the present embodiment is implanted in the heart H such that all electrode poles 113 - 115 he within the right ventricle RV of the heart H. At a distal end 112 of the electrode lead, a tip electrode 114 of the electrode lead 11 is deeply implanted in the apex of the right ventricle RV of the heart H. Between the shock coil 115 and the tip electrode 114 a ring electrode 113 is disposed and connected on the electrode lead 11. The electrode poles 113, 114 and 115 serve to sense cardiac signals for processing within the generator device 10 of the implantable medical device 1, such that based on sensed signals an arrhythmia may be identified and a shock pulse may be generated for providing for a defibrillation therapy.

[0063] The generator device 10 generally comprises a processing circuitry 102 for controlling operation of the implantable medical device 1. In addition, the generator device 10 comprises a pulse generation circuitry 103, a memory unit (not shown in Fig. 1) and an energy supply 104, in particular in the shape of an electrochemical battery.

[0064] The processing circuitry 102 in particular serves to process signals sensed via an electrode pole arrangement formed by the electrode poles 113, 114, 115 arranged on the lead 11 and additional poles, such as the housing 100 of the generator device 10. The different poles of the electrode pole arrangement form pairs of electrode poles in between which sense vectors are spanned, the different sense vectors allowing to sense intracardiac electrocardiogram signals from the patient’s heart H with a different spatial sensitivity, hence allowing to sense and process information from the patient’s heart H in a multichannel processing.

[0065] The implantable medical device 1 may comprise a communication interface for communicating with an external device 2, for example within a home-monitoring system.

[0066] Fig. 2 shows another embodiment of an implantable medical device 1 according to the present invention, which in the shown, non-limiting embodiment of Fig. 2 is an implantable cardioverter defibrillator device designed as a non-transvenous implantable cardioverter defibrillator device, which is implanted such that it is completely external to the heart H.

[0067] The implantable medical device 1 in the embodiment of Fig. 2 comprises a generator device 10 encapsulated within a housing 100, and a lead 11 connected to the generator device 10 at a proximal end 111 and carrying electrode poles 113, 114 as well as a shock electrode 115 in the shape of a coil formed on a distal portion close to a distal end 112 of the lead 11. The electrode poles 113, 114, for example formed as ring electrodes on either side of the shock electrode 115, serve to sense cardiac signals for processing within the generator device 10 of the implantable medical device 1, such that based on sensed signals an arrhythmia may be identified and a shock pulse may be generated for providing for a defibrillation therapy.

[0068] The implantable medical device 1, in the embodiment of Fig. 2, is designed for a non- transvenous implantation, that is an implantation external to the patient’s heart H. In particular, the lead 11 connected to the generator device 10 shall rest outside of the patient’s heart H and shall not extend transvenously into the heart, the shock electrode 115 hence, in an implanted state, being placed outside of the heart H for providing for a defibrillation therapy.

[0069] For example, the generator device 10 may be implanted subcutaneously in a patient. The lead 11, with a lead body 110, may extend from the generator device 10 towards the sternum of the patient, the lead 11 for example tunneling through tissue in the region of the sternum and being placed beneath the sternum of the patient.

[0070] The implantable medical device 1 may comprise a communication interface for communicating with an external device 2, for example within a home-monitoring system.

[0071] Referring now to Fig. 3, the generator device 10 generally comprises a processing circuitry 102 for controlling operation of the implantable medical device 1. In addition, the generator device 10 comprises a pulse generation circuitry 103, a memory unit (not shown in Figs. 2 and 3) and an energy supply 104, in particular in the shape of an electrochemical battery.

[0072] The processing circuitry 102 in particular serves to process signals sensed via an electrode pole arrangement formed by the electrode poles 113, 114, 115 arranged on the lead 11 and additional poles, such as the housing 100 of the generator device 10. The different poles of the electrode pole arrangement form pairs of electrode poles in between which sense vectors A, B, C, D are spanned, as illustrated in Fig. 3, the different sense vectors A, B, C, D allowing to sense electrocardiogram signals from the patient’s heart H with a different spatial sensitivity, hence allowing to sense and process information from the patient’s heart H in a multichannel processing.

[0073] Fig. 4 shows yet another embodiment of the implantable medical device according to the present invention. The embodiment of Fig. 4, which is similar to the embodiment shown in Fig. 1 , shows an implantable medical device 1 comprising a generator device 10 and one or multiple electrode leads 11 connected to the generator device 10.

[0074] The electrode lead 11 comprises for example a tip electrode pole 113 and a ring electrode pole 114 as well as a shock electrode 115, wherein other combinations of electrode poles on one or multiple electrode leads 11 and / or on a housing 100 of the generator device 10 are conceivable.

[0075] The housing 100 of the generator device 10 encloses a processing circuitry 102, the processing circuitry 102 implementing, for example by software, a variety of different functional units for processing signals and for controlling operation of the implantable medical device 1.

[0076] For example, the processing circuitry 102 comprises a therapeutic unit 1020 serving to control a therapy, for example for generating and outputting stimulation signals such as cardiac pacing pulses and / or defibrillation shock pulses.

[0077] A measuring unit 1021 is configured to conduct measurements, for example impedance measurements, temperature measurements, blood pressure measurements or the like.

[0078] In addition, electrical signals are sensed, using an electrode pole arrangement formed by electrode poles 113, 114, 115 of one or multiple electrode leads 11 and potentially the housing 100 of the generator device 10, across one or multiple sense vectors. Such electrical sense signals are sensed using a sensing unit 1022 and are forwarded to an evaluation unit 1023 for evaluating and processing the sensed signals. Processed signals are then provided to a coding unit 1025, which forwards coded signals to a memory unit 1026, comprising, for example, a cyclic buffer. In addition, a detection unit 1024 may be configured to detect an intrinsic cardiac rhythm, bradycardia or tachycardia arrhythmia events or other events.

[0079] A communication unit 1027 is configured to establish a communication link L to an external device 2 and to communicate information in particular with respect to compressed, coded sense signals to the external device 2. The external device 2 may for example be a smart phone or a tablet computer of the patient. Communication may for example be established using a common standardized communication protocol, for example based on Bluetooth, such as Bluetooth Low Energy (BLE), or Zigbee. In addition, a programming device 3 may be used to program the implantable medical device 1 in an implanted state. A remote device 4, such as a remote server system in the context of a home monitoring system, may be stationed at a remote location and may be in communication connection with the external device 2 and / or the programming device 3 via a public communication network, such as the Internet.

[0080] Referring now to Fig. 5, during operation of the implantable medical device 1 an electrical sense signal S is obtained by the processing circuitry 102 of the implantable medical device 1 using the electrode pole arrangement. Within the processing circuitry 102, in particular at the sensing unit 1022 and the evaluation unit 1023, herein, the sense signal S is obtained in a sampled fashion at a first sampling rate to obtain first signal samples Si at the first sampling rate. Based on the signal samples Si the sense signal S is processed, and events E are detected and classified within the evaluation unit 1023, potentially in combination with the detection unit 1024. Such events E may for example relate to certain signal portions, such as QRS complexes, and may for example be determined according to a threshold crossing or according to signal maxima relating e.g. an R peak of a QRS waveform, as illustrated in Fig. 5.

[0081] For communicating information to the external device 2, the sensed signal samples Si obtained at the first sampling rate are compressed in the coding unit 1025 in order to derive second signal samples Sk at a reduced second sampling rate based on the first signal samples Si. The first sampling rate of the first signal samples Si may for example be at 512 Hz, and the second sampling rate of the second signal samples Sk may for example be at 128 Hz, such that the sampling rate of the second signal samples Sk is reduced by a factor of 4 in comparison to the sampling rate of the first signal samples Si.

[0082] In addition, the second signal samples Sk may be coded at a reduced bit resolution, each second signal sample Sk being expressed for example by 7 bit, whereas each first signal sample Si for example is expressed by 10 bit.

[0083] In Fig. 5, the first signal samples Si are illustrated by circles on the graph of the signal S, where circles with a black filling denote sampling times coinciding with the sampling times of the second signal samples Sk and circles with a white filling denote sampling times in between the sampling times of the second signal samples Sk. The boxes numbered 1 to 17 below the graph of the signal S denote the second signal samples Sk associated with the sampling times of the black-filled circles.

[0084] As illustrated in Fig. 5, event markers Ml, M2, M3 are generated according to events E as identified based on the sense signal S. Event markers Ml, M2, M3 herein are associated with certain second signal samples Sk. In the example of Fig. 5, the event marker Ml is associated with the second signal sample Sk having the number 6, the event marker M2 is associated with the second signal sample Sk having the number 10, and the third event marker M3 is associated with the second signal sampling Sk having the number 14.

[0085] Referring now to Fig. 6, each second signal sample Sk is for example coded by a 1-byte codeword, wherein the sample value is expressed by 7 bits denoted by V in the box at the top of Fig. 6 and an additional leading bit has a value of “1” indicating, in a bitstream as communicated by the implantable medical device 1 towards the external device 2, that with the instant byte a sample value of a signal sample is transmitted.

[0086] Each event marker Ml, M2, M3 may indicate a different kind of events and thus may be either expressed by a onebyte sequence (event markers Ml, M3, second box in Fig. 6), a threebyte sequence (event marker M2 in the third box of Fig. 6) or by a five-byte or seven-byte sequence. An event may have a required storage space which is defined by a number of N determined bit. In this case, subsequent M-byte are determined according to the coding protocol. An event may be derived from the electrical sense signal S or may consist of or comprise a status information of an implant software.

[0087] If the event marker Ml, M3 is coded by a onebyte sequence (second box in Fig. 6), the leading two bits have the value “00” and express, in a bitstream, that the byte relates to an event marker Ml, M3, wherein the trailing 6 bits denoted by M in Fig. 6 comprise information about the event E associated with the event marker Ml, M3. If the event marker M2 is coded by three byte (third box in Fig. 6), the leading two bits of the first byte have the value “00” and express, in a bitstream, that the byte relates to an event marker M2, and the trailing 6 bits of the first byte as well as all bits of the two further bytes denoted by M in Fig. 6 comprise information about the event E associated with the event marker M2. In addition, in connection with certain second signal samples Sk a timestamp T may be transmitted, the timestamp T being expressed by one byte, where the leading two bits have the value “01”, hence indicating that the instant byte relates to a timestamp T and the trailing 6 bit denoted by T in the box at the bottom of Fig. 6 carrying the timestamp information.

[0088] Referring now to Fig. 7, the second signal samples Sk are derived from the first signal samples Si in order to compress the data for transmission to the external device 2. For example, in one embodiment each second signal sample Sk is associated with a time span TS which encompasses four first signal samples S;. The sample value of the second signal sample Sk may for example be determined according to the maximum value of the first signal samples Si in the time span TS.

[0089] In the example of Fig. 7, the second signal sample Sk numbered 1* is associated with the time span TS encompassing the first signal samples Si numbered 1 to 4. The first signal sample Si with number 4 herein exhibits the largest sample value SV, such that the sample value of the second signal sample Sk numbered 1* is set to the signal value SV of the first signal sample Si with number 4.

[0090] Likewise, the second signal sample numbered 2* is set to the sample value SV of the first signal sample Si have the number 6, and the second signal sample Sk having the number 3* is set to the sample value SV of the the first signal sample Si having the number 9.

[0091] Each second signal sample Sk may for example be associated with a sampling time tk corresponding to the sampling time of the latest first signal sample Si in the time span TS associated with the particular second signal sample Sk. As visible from Fig. 7, as the first signal samples Si used for the processing and evaluation within the processing circuitry 102 have an increased sampling resolution, there may be a time difference DI, D2 between the sampling time tk of a second signal sample Sk and the sampling time t; of a corresponding first signal sample Si according to whose sample value SV the second signal sample Sk is set. The reduced sampling rate of the second signal samples Sk, hence, may give rise to inaccuracies, as the sample value of a particular second signal sample Sk potentially has not occurred at the exact sampling time tk of the second signal sample Sk, but at a different sampling time t; of an associated first signal sample Si, illustrated in Fig. 7 according to the time differences DI, D2. As illustrated in Fig. 8, when displaying a sensed signal curve according to the second signal samples Sk, the resulting curve C2 may be somewhat different than a curve Cl which is obtained if the actual sampling times of the first signal samples Si giving rise to the sample values SV of the second signal samples Sk are taken into account. For example, when examining slope values SL1, SL2, this may actually play a role for an assessment.

[0092] In addition, if an event marker Ml is (only) associated with a second signal sample Sk and hence is associated with the temporal resolution of the second signal samples Sk, there may be a time difference between the event marker Ml and the sampling time for which the event E actually has been identified. In the example of Fig. 7, the event E has for example been determined according to the maximum of the first signal samples Si at sampling time t; (corresponding to the first signal sample Si with number 6 in Fig. 7), whereas the event marker Ml is associated with the second signal sample Sk with number 2* at sampling time tk. There hence is a time difference DI between the time of the event marker Ml and the occurrence of the actual event E.

[0093] Referring now to Fig. 9, in order to allow the external device 2 for a processing and displaying of information with respect to the event marker Ml with an improved timing resolution, it is proposed to determine and transmit an additional timing information TI for an event marker Ml .

[0094] The timing information TI is expressed by 2 bit (denoted as “TT”) and is transmitted together with the event marker Ml. The timing information TI expresses the relative timing determined according to the time difference DI between the actual time of the event E, corresponding to the sampling time t; of the first signal sample Si with number 6 at which the event E has been determined, and the sampling time tk of the second signal sample Sk with number 2*, with which the event marker Ml is transmitted.

[0095] In the example of Fig. 9, the sampling rate of the first signal samples Si is for example 512 Hz, whereas the sampling rate of the second signal samples Sk is 128 Hz. There hence is a ratio between the first sampling rate and the second sampling rate of Z=4. Four first signal samples Si hence fall into the time span TS associated with each second signal sample Sk.

[0096] Accordingly, the relative timing information may have four values, in that the relative timing information may point to any of the sampling times of the first signal samples Si falling into the time span TS of a particular second sample Sk. The timing information TI hence may have four states, and correspondingly can be expressed by 2 bit.

[0097] The timing information TI expresses the relative timing with relation to the associated second signal sample Sk. As illustrated in Fig. 9, the timing information TI may indicate the relative timing DI* between the sampling time tk of the actual second signal sample Sk with number 2* and the sampling time t; of the first signal sample Si at which the event E has been determined, corresponding to the first signal sample Si with number 6 in the example of Fig. 9.

[0098] In another embodiment, shown in Fig. 9, the timing information TI may indicate the relative timing DI** between the prior second signal sample Sk with number 1* and the sampling time tk of the first signal sample Si at which the event E has been determined.

[0099] Because an additional timing information TI is transmitted together with the event marker Ml, the event marker Ml may be analyzed and displayed by the external device 2 or any other device 3, 4 in direct or indirect communication connection with the implantable medical device 1 with a temporal resolution corresponding to the first signal samples Si. Marker information hence may be analyzed and displayed with increased temporal resolution, such that information about the occurrence of events E is more accurate and is not limited to the temporal resolution of the compressed second signal samples Sk.

[0100] The number of bits required for the additional timing information TI may be determined according to the equation 2N=Z, where N is the number of bits and Z is the ratio between the first sampling rate and the second sampling rate. For a ratio of 4 (e.g. 512 Hz: 128 Hz), 2 bit are required. For a ratio of 8 (e.g. 2048 Hz: 256 Hz), 3 bit are required.

[0101] The additional timing information TI may be transmitted as additional bits in addition to marker bytes carrying the event marker information, as illustrated in Fig. 6. In one embodiment, the timing information TI may be transmitted as part of the marker information and hence within the byte(s) of an event marker Ml -M3.

[0102] In one embodiment, a timing information may not only be transmitted for an event marker, but for example for each second sample Sk, such that the relative positioning of each second sample Sk within an associated time stamp is indicated. This for example may be used to more accurately assess a slope value SL1, as illustrated in Fig. 8.

[0103] Referring now to Fig. 11, in one embodiment, alternatively or in addition to transmitting additional timing information TI together with an event marker Ml to M3, the processing circuitry 102 of the implantable medical device 1 may be configured to switch between different modes of operation in order to, in a regular mode, communicate information about signal samples at a reduced sampling rate to an external device 2 and, in a mode of increased sampling resolution, communicate information about signal samples at an increased sampling rate to an external device 2.

[0104] As illustrated in Fig. 11, a sense signal S may be sampled at a first sampling rate to obtain first signal samples Si for internal processing and evaluation. In a regular mode, the first signal samples Si are compressed and coded to obtain second signal samples Sk at a reduced, second sampling rate, and such second signal samples Sk are communicated to the external device 2, as it has been explained above.

[0105] The implantable medical device 1 herein is configured to switch, at a switching time XI, to a mode of increased sampling resolution, in which no or limited compression of the first signal samples Si takes place. Namely, in the example of Fig. 11 second samples Sk in the mode of increased sampling resolution are obtained from the first signal samples Si at the same sampling rate, such that the sampling rate is not reduced. In order to compress data, herein, for example a bit resolution may be decreased, such that the second signal samples Sk are for example presented by a 7-bit word, whereas the first signal samples Si are expressed each by 10 bit.

[0106] In the example of Fig. 11, the first signal samples Si used for internal processing are numbered 1 to 17 and are expressed by the circles on the curve of the signal S. In a regular mode, second signal samples Sk at a reduced sampling rate are derived from the first signal samples Si, wherein in the example of Fig. 11 the regular mode is carried out prior to switching time XI and subsequent to switching time X2, yielding second signal samples Sk with numbers 1 * and 11 * derived from the first signal samples Si numbered 1 to 4 and 14 to 17. In a period X between the switching times XI, X2, however, the processing circuitry 102 operates in the mode of increased sampling solution, such that second signal samples Sk with numbers 2* to 10* are derived from first signal samples Si with numbers 5 to 13, the second signal samples Sk being obtained at the same sampling rate as the first signal samples Si.

[0107] The switching times XI, X2 may for example be chosen such that a particular signal waveform is covered by the mode of increased sampling resolution. For example, the switching times XI, X2 may be determined based on a prior interval length, based on a detected signal feature such as a P wave peak, an R peak or the end of a T wave, based on a triggering by an atrial channel, or based on morphological criteria of a prior event.

[0108] If a cyclic buffer (memory unit 1026, see Fig. 4) is used, the mode of increased sampling resolution may also be activated in retrospect in that first signal samples Si are buffered and are processed and compressed with some time delay to the second signal samples Sk based on an analysis of signal features as indicated by the first signal samples Si.

[0109] In the mode of increased sampling resolution, an event marker Ml may be transmitted in association with a second signal sample Sk, wherein no additional timing information is to be transmitted because the timing resolution of the second signal samples Sk beneficially corresponds to the timing resolution of the first signal samples Si.

[0110] At the switching times XI, X2 switching event markers SI, S2 may be transmitted from the implantable medical device 1 to the external device 2 in order to notify the external device 2 that second signal samples Sk in between the switching times XI, X2, as indicated by the switching event markers SI, S2, are obtained at an increased sampling solution.

[0111] The sampling rate of the second signal samples Sk in the mode of increased sampling resolution may be fixed, for example according to a programming at the initial startup of the device 1. In another embodiment, the sampling rate of the second signal samples Sk in the mode of increased sampling resolution may be adaptive, for example in that the sampling rate in the mode of increased sampling resolution depends on a particular type of signal feature which shall be covered by the increased sampling resolution.

[0112] The idea underlying the invention is not limited to the embodiments described above, but may be implemented in an entirely different fashion. The implantable medical device may be a cardiac device, in particular a cardiac stimulation device such as a cardiac pacemaker device or a cardiac defibrillation device. In other embodiments, the implantable medical device may be a cardiac monitoring device or a sensor device. In yet other embodiments, the implantable medical device may be a neuro-stimulation device or another device configured for implantation in a patient and for receiving electrical signals during operation of the patient.

[0113] List of reference numerals

[0114] 1 Implantable medical device

[0115] 10 Generator device

[0116] 100 Housing

[0117] 101 Connection block

[0118] 102 Processing circuitry

[0119] 1020 Therapy unit

[0120] 1021 Measuring unit

[0121] 1022 Sensing unit

[0122] 1023 Evaluation unit

[0123] 1024 Detection unit

[0124] 1025 Coding unit

[0125] 1026 Memory unit

[0126] 1027 Communication unit

[0127] 103 Pulse generation circuitry

[0128] 104 Energy supply (battery)

[0129] 11 Electrode lead

[0130] 110 Lead body

[0131] 111 Proximal end

[0132] 112 Distal end

[0133] 113, 114 Electrode pole

[0134] 115 Shock electrode (coil)

[0135] 2 External device

[0136] 3 Programming device

[0137] 4 Remote device

[0138] A-D Reception vector b Bit

[0139] Cl, C2 Curve

[0140] D1, D2 Timing distance

[0141] D 1 * , D 1 * * Relative timing

[0142] E Event

[0143] H Heart RA Right atrium

[0144] RV Richt ventricle

[0145] LA Left atrium

[0146] LV Left ventricle

[0147] L Communication link

[0148] Ml, M2, M3 Event marker

[0149] S Signal

[0150] Si Signal sample

[0151] Sk, Sk’ Signal sample

[0152] SL1, SL2 Slope

[0153] SV Sample value

[0154] SI, S2 Switching event marker

[0155] T Time stamp h Sampling time

[0156] TI Timing information tk Sampling time

[0157] TS Time span

[0158] X Period of increased resolution

[0159] XI, X2 Switching time

Claims

Claims1. An implantable medical device (1), comprising an electrode pole arrangement (113-115) for sensing electrical signals, a processing circuitry (102) for processing a sensed signal (S) obtained using the electrode pole arrangement (113-115), and a memory unit, said processing circuitry (102) being configured to: obtain first signal samples (Si) indicative of the sensed signal (S) at a first sampling rate, derive, based on the first signal samples (Si), second signal samples (Sk) at a second sampling rate smaller than the first sampling rate, each second signal sample (Sk) being associated with a time span (TS) encompassing a multiplicity of first signal samples (S , identify, based on the sensed signal (S), an event (E) and generate, for said event (E), an event marker (Ml -M3) in association with an associated second signal sample, and store information indicative of said second signal samples (Sk) and said event marker (Ml -M3) in the memory unit, characterized in that the processing circuitry (102) is further configured to determine, for said event marker (Ml -M3), timing information (TI) indicative of a relative timing (DI*, DI**) of said event marker (M1-M3) within said time span (TS) of the associated second signal sample and to store said timing information (TI) in the memory unit.

2. The implantable medical device (1) according to claim 1, characterized in that the first sampling rate is an integer multiple of said second sampling rate.

3. The implantable medical device (1) according to claim 1 or 2, characterized in that the first sampling rate lies in a range between 64 Hz and 2048 Hz, and the second sampling rate lies in a range between 32 Hz and 1024 Hz.

4. The implantable medical device (1) according to one of claims 1 to 3, characterized in that the processing circuitry (102) is configured to derive a sample value of each of the second signal samples (Sk) according to a maximum value of first signal samples (Si) in the time span (TS) associated with the second signal sample (Sk).

5. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (102) is configured to identify said event (E) at a first sampling time (ti) of an associated first signal sample (Si), wherein said timing information (TI) is indicative of a relative timing (DI*, DI**) of the first sampling time (ti) in the time span (TS) of the associated second signal sample.

6. The implantable medical device (1) according to claim 5, characterized in that the relative timing (DI*, DI**) is measured with respect to a second sampling time (tk) of the associated second signal sample or with respect to a third sampling time of a second signal sample prior to the associated second signal sample.

7. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (102) is configured to obtain said first signal samples (Si) at a first bit resolution and to code said second signal samples (Sk) for storing in the memory unit at a second bit resolution smaller than the first bit resolution.

8. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (102) is configured to code said timing information (TI) using a code word comprising N bit, where 2N= Z and Z corresponds to the ratio of the first sampling rate and the second sampling rate.

9. The implantable medical device (1) according to one of the preceding claims, characterized in that the processing circuitry (102) is configured to derive, in a regular mode, said second signal samples (Sk) at said second sampling rate and, in a mode of increased sampling resolution, at a third sampling rate larger than said second sampling rate and to store information indicative of said second signal samples (Sk) in the memory unit.

10. The implantable medical device (1) according to claim 9, characterized in that the third sampling rate is equal to the first sampling rate.

11. The implantable medical device (1) according to claim 9 or 10, characterized in that the processing circuitry (102) is configured to switch, at a first switching time (XI), from theregular mode to said mode of increased sampling resolution and, at a second switching time (X2), from the increased sampling resolution to the regular mode.

12. The implantable medical device (1) according to claim 11, characterized in that the processing circuitry (102) is configured to generate, at the first switching time (XI) and / or at the second switching time (X2), a switching event marker (SI, S2) and to store information relating to said switching event marker (SI, S2) in the memory unit.

13. An implantable medical device (1), comprising an electrode pole arrangement (113-115) for sensing electrical signals, a processing circuitry (102) for processing a sensed signal (S) obtained using the electrode pole arrangement (113-115), and a memory unit, said processing circuitry being configured to: obtain first signal samples (Si) indicative of the sensed signal (S) at a first sampling rate, derive, based on the first signal samples (Si), second signal samples (Sk) at a second sampling rate smaller than the first sampling rate, each second signal sample (Sk) being associated with a time span (TS) encompassing a multiplicity of first signal samples (S , identify, based on the sensed signal (S), an event (E) and generate, for said event (E), an event marker (Ml -M3) in association with an associated second signal sample, and store information indicative of said second signal samples (Sk) and said event marker (Ml -M3) in the memory unit, characterized in that the processing circuitry (102) is further configured to derive, in a regular mode, said second signal samples (Sk) at said second sampling rate and, in a mode of increased sampling resolution, at a third sampling rate larger than said second sampling rate and to store information indicative of said second signal samples (Sk) in the memory unit.

14. Method for storing electrical signal data in an implantable medical device (1) according to any one of claims 1 to 12, comprising the steps: obtaining first signal samples (Si) indicative of the sensed signal (S) at a first sampling rate,deriving, based on the first signal samples (Si), second signal samples (Sk) at a second sampling rate smaller than the first sampling rate, each second signal sample (Sk) being associated with a time span (TS) encompassing a multiplicity of first signal samples (S , identifying, based on the sensed signal (S), an event (E) and generate, for said event (E), an event marker (Ml -M3) in association with an associated second signal sample, and storing information indicative of said second signal samples (Sk) and said event marker (Ml -M3) in the memory unit, determining, for said event marker (Ml -M3), timing information (TI) indicative of a relative timing (DI*, DI**) of said event marker (Ml -M3) within said time span (TS) of the associated second signal sample, and storing said timing information (TI) in the memory unit.

15. Method for storing electrical signal data in an implantable medical device (1) according to claim 13, comprising the steps: obtaining first signal samples (Si) indicative of the sensed signal (S) at a first sampling rate, deriving, based on the first signal samples (Si), second signal samples (Sk) at a second sampling rate smaller than the first sampling rate, each second signal sample (Sk) being associated with a time span (TS) encompassing a multiplicity of first signal samples (Si), identifying, based on the sensed signal (S), an event (E) and generate, for said event (E), an event marker (Ml -M3) in association with an associated second signal sample, and storing information indicative of said second signal samples (Sk) and said event marker (Ml -M3) in the memory unit, deriving, in a regular mode, said second signal samples (Sk) at said second sampling rate and, in a mode of increased sampling resolution, at a third sampling rate larger than said second sampling rate, and storing information indicative of said second signal samples (Sk) in the memory unit.

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