Implantable medical device employing electrode integrity monitoring

Abstract

The present invention relates to an implantable medical device (1) for stimulating a human or animal heart. During operation, the implantable medical device (1) executes a method comprising the following steps: a) detecting a right ventricular electric signal, the detected right ventricular electric signal comprising a plurality of right ventricular events (13); b) calculating a mean right ventricular interval (15) from a predeterminable number of at least some right ventricular events (13) of the plurality of right ventricular events (13); c) detecting a left ventricular electric signal with the second electrode (9), the detected left ventricular electric signal comprising a plurality of left ventricular events (16); d) calculating a mean left ventricular interval (18) from a predeterminable number of at least some left ventricular events (16) of the plurality of left ventricular events (16); e) if at least one of the mean right ventricular interval (15) and the mean left ventricular interval (18) falls below a value lying in the range of from 200 ms to 2000 ms, determining a deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18); f) if the deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18) is bigger than a threshold, triggering a storing of at least a part of the detected right ventricular electric signal and / or of at least a part of the detected left ventricular electric signal in the memory unit (33) to allow a later evaluation of the stored part of the right ventricular electric signal and / or of the left ventricular electric signal.

Description

[0001] IMPLANTABLE MEDICAL DEVICE EMPLOYING ELECTRODE INTEGRITY MONITORING

[0002] The present invention relates to an implantable medical device according to the preamble of claim 1 and to a method for operating an implantable medical device according to the preamble of claim 15.

[0003] Prior art describes a plurality of possibilities to detect electrode integrity problems (electrode malfunctions) of an implantable medical device for cardiac stimulation.

[0004] According to an impedance-based approach, exceeding an absolute threshold or falling below an absolute threshold during painless monitoring of the shock and stimulation activity of an implantable medical device is used to detect an electrode integrity problem. Furthermore, a quasi-continuous impedance monitoring can be performed. Then, conspicuous, strong impedance changes on a sample-to- sample basis at a comparatively high sampling rate can provide information on an electrode integrity problem.

[0005] According to a timing-based approach, a short interval counter can be applied. An increased number of unphy si ologi cal short intervals (having a duration of approximately 110 ms to 140 ms) triggers further evaluation of the detected signal or directly indicates a suspected electrode integrity problem. Other timing patterns in the detected electric signal can also be used for triggering further evaluation of the detected signal.

[0006] While impedance-based approaches provide a strong indicator that an electrode integrity problem exists, they allow a continuous monitoring of the electrode integrity only under significantly increased power consumption. Exclusively time-based approaches, on the other hand, require that the electrode fault can be detected as oversensing in a bipolar derivation, typically between the right ventricular tip electrode pole and the right ventricular ring electrode pole of the used electrode.

[0007] It is an object of the present invention to provide a continuous energy-saving monitoring of cardiac electric signals to identify indicators for electrode integrity problems and to allow a later thorough analysis of the respective signals.

[0008] This object is achieved with an implantable medical device for stimulating a human or animal heart according to claim 1. Such an implantable medical device comprises a processor, a memory unit, a stimulation unit, and a detection unit. The stimulation unit serves for stimulating a human or animal heart. The detection unit serves for detecting an electric signal of the same heart, i.e., a cardiac electric signal. The detection unit comprises a first electrode for detecting right ventricular electric signals and a second electrode for detecting left ventricular electric signals. In this context, the first electrode comprises a first electrode pole and a second electrode pole. Likewise, the second electrode comprises a third electrode pole and a fourth electrode pole.

[0009] According to an aspect of the present invention, the memory unit comprises a computer-readable program that causes the processor to perform the steps explained in the following when executed on the processor.

[0010] In a first step, a right ventricular electric signal is detected with the first electrode. This is done, e.g., during a first time period. In this context, the detected right ventricular electric signal comprises a plurality of right ventricular events.

[0011] Afterwards, a mean right ventricular interval is calculated from a predetermined number of at least some right ventricular events of the plurality of right ventricular events. The predeterminable number of at least some right ventricular events of the plurality of right ventricular events falls within a first time window.

[0012] In another method step, a left ventricular electric signal is detected with the second electrode. This is also done, e.g., during the first time period or during at least a part of the first time period that covers the first time window. In this context, the detected left ventricular electric signal comprises a plurality of left ventricular events.

[0013] In another step, a mean left ventricular interval is calculated from a predetermined number of at least some left ventricular events of the plurality of left ventricular events. The predeterminable number of at least some left ventricular events of the plurality of left ventricular events falls within a second time window, wherein the second time window comprises at least the first time window. In an embodiment, the second time window is identical or essentially identical to the first time window.

[0014] Afterwards, it is determined whether the mean right ventricular interval and / or the mean left ventricular interval falls below a value lying in a range of from 200 ms to 2000 ms, in particular from 250 ms to 1900 ms, in particular from 300 ms to 1800 ms, in particular from 350 ms to 1700 ms, in particular from 400 ms to 1600 ms, in particular from 450 ms to 1500 ms, in particular from 500 ms to 1400 ms, in particular from 600 ms to 1300 ms, in particular from 700 ms to 1200 ms, in particular from 800 ms to 1100 ms, in particular from 900 ms to 1000 ms. If this is the case, an electrode integrity problem might exist. Therefore, the general possibility of triggering storing the detected cardiac electric signal is made available. If the mean right ventricular interval and / or the mean left ventricular interval exceeds the beforementioned value, it is rather unlikely that an electrode integrity problem exists. Therefore, in such a case, no possibility of triggering storing the detected cardiac electric signal is made possible. Rather, the method is then terminated.

[0015] In a further method step that is only performed if the mean right ventricular interval and / or the mean left ventricular interval falls below the value lying in the beforementioned range of from 200 ms to 2000 ms, a deviation is determined between the mean right ventricular interval and the mean left ventricular interval.

[0016] If this deviation between the mean right ventricular interval and the mean left ventricular interval is bigger than 20%, storing at least a part of the detected cardiac electric signal in the memory unit is triggered in a further method step. The term “cardiac electric signal” as used herein covers the detected right ventricular electric signal and / or the detected left ventricular electric signal. If the deviation is smaller than 20 %, the method is terminated without triggering such storing. Triggering such storing allows a later evaluation of the stored part of the cardiac electric signal, i.e., a deeper analysis of the cardiac electric signal, e.g., outside the implantable medical device with a computer having more computing capacity and being less limited in terms of power consumption than the implantable medical device is.

[0017] This implantable medical device represents a highly performant system for early detection of electrode integrity problems (electrode failures) based on an evaluation of the detected right ventricular signal and the detected left ventricular electric signal, e.g., a detected intracardiac electrogram (IEGM). The implantable medical device does not require a specific design of its system components. They can be chosen and operated such that the overall sensitivity and the overall specificity can be adjusted to the respective needs of the intended kind of application of the implantable medical device. Thus, irrespective of enabling a detailed analysis of suspicious areas of the detected cardiac electric signal to detect electrode integrity problems, the implantable medical device enables a 24 / 7 monitoring of a patient's heart (i.e., it can be operated with a high overall sensitivity). In addition, it does not require a complex sorting-out of false-positive trigger events for storing the detected cardiac electric signal that takes place when applying more demanding approaches or a higher calculation complexity based on a predeterminable dataset (i.e., the implantable medical device can be operated with a high specificity).

[0018] It is not important for the presently claimed and described subject matter how the stored cardiac electric signal is finally evaluated or analyzed. Rather, the presently described and claimed solution merely aims in providing sensible and reliable causes of triggering the storing of at least a part of the detected cardiac electric signal in case of a suspected electrode integrity problem. The sored signal can afterwards be analyzed to find out whether there is indeed an electrode integrity problem.

[0019] In an embodiment, the implantable medical device is an implantable pulse generator (IPG), an implantable cardioverter-defibrillator (ICD), or a device for cardiac resynchronization therapy (CRT). In an embodiment, the predetermined number of right ventricular events used for calculating the mean right ventricular interval lies in a range of from 5 to 17, in particular from 6 to 16, in particular from 7 to 15, in particular from 8 to 14, in particular from 9 to 13, in particular from 10 to 12. Typically, the right ventricular events used for calculating the mean right ventricular interval are the youngest (or newest) right ventricular events detected with the first electrode.

[0020] In an embodiment, the predetermined number of left ventricular events used for calculating the mean left ventricular interval lies in a range of from 5 to 17, in particular from 6 to 16, in particular from 7 to 15, in particular from 8 to 14, in particular from 9 to 13, in particular from 10 to 12. Typically, the left ventricular events used for calculating the mean left ventricular interval are the youngest (or newest) left ventricular events detected with the second electrode.

[0021] In an embodiment, the second time window comprises a first additional time interval with respect to the first time window. Expressed in other words, the second time window is longer than the first time window due to the first additional time interval. This first additional time interval covers a range from 0.1 to 5 seconds, in particular from 0.2 to 4.5 seconds, in particular from 0.3 to 4 seconds, in particular from 0.4 to 3.5 seconds, in particular from 0.5 to 3 seconds, in particular from 0.6 to 2.5 seconds, in particular from 0.7 to 2 seconds, in particular from 0.8 seconds to 1.5 seconds, in particular from 0.9 seconds to 1 second. In this context, the first additional time interval lies prior to the first of the right ventricular events used for calculating the mean right ventricular interval.

[0022] In an embodiment, the second time window comprises a second additional time interval with respect to the first time window. Expressed in other words, the second time window is longer than the first time window due to the second additional time interval. This second additional time interval covers a range from 0.1 to 5 seconds, in particular from 0.2 to 4.5 seconds, in particular from 0.3 to 4 seconds, in particular from 0.4 to 3.5 seconds, in particular from 0.5 to 3 seconds, in particular from 0.6 to 2.5 seconds, in particular from 0.7 to 2 seconds, in particular from 0.8 seconds to 1.5 seconds, in particular from 0.9 seconds to 1 second. In this context, the second additional time interval lies after the last of the right ventricular events used for calculating the mean right ventricular interval.

[0023] In an embodiment, the computer-readable program causes the processor to recalculate the mean right ventricular interval and / or the mean left ventricular interval with every newly detected right ventricular event. Thus, the detection of another right ventricular event is decisive for defining the right ventricular events used for calculating the mean right ventricular interval as well as the left ventricular events used for calculating the mean left ventricular interval.

[0024] In an embodiment, the computer-readable program causes the processor to recalculate the mean right ventricular interval with every newly detected right ventricular event and to recalculate the mean left ventricular interval with every newly detected left ventricular event. Thus, in this embodiment, an updating of the mean right ventricular interval depends on the newly detected right ventricular event, wherein an updating of the mean left ventricular interval depends on a newly detected left ventricular event.

[0025] In an embodiment, the computer-readable program causes the processor to recalculate the mean right ventricular interval and / or the mean left ventricular interval after a predetermined second time period has passed. Then, updating the mean right ventricular interval and / or the mean left ventricular interval does not depend on a detection of a novel right ventricular event and / or a novel left ventricular event, but is rather performed in regular intervals.

[0026] In an embodiment, the predetermined second time period lies in a range of from 1 to 10 seconds, in particular from 2 to 9 seconds, in particular from 3 to 8 seconds, in particular from 4 to 7 seconds, in particular from 5 to 6 seconds.

[0027] In an embodiment, the computer-readable program causes the processor to calculate the deviation between the mean right ventricular interval and the mean left ventricular interval by an equation that comprises either a quotient between the mean right ventricular interval and the mean left ventricular interval or a quotient between the mean left ventricular interval and the mean right ventricular interval. By calculating such quotient between the two calculated mean ventricular intervals, a deviation of one of these intervals from the respective other can be determined in a particularly easy and reliable way.

[0028] In an embodiment, the computer-readable program causes the processor to calculate the deviation between the mean right ventricular interval and the mean left ventricular interval by the following equation (I):

[0029] / MLVI\ 100 * > x (I)

[0030]

[0031] I1” MRVl)

[0032] In this context,

[0033] ML VI denotes the mean left ventricular interval,

[0034] MR VI denotes the mean right ventricular interval,

[0035] x denotes a threshold.

[0036] According to an embodiment, threshold x is at least 0.2.

[0037] In an embodiment, x lies in a range of from 0.2 to 2.0, in particular from 0.3 to 1.9, in particular from 0.4 to 1.8, in particular from 0.5 to 1.7, in particular from 0.6 to 1.6, in particular from 0.7 to 1.5, in particular from 0.8 to 1.4, in particular from 0.9 to 1.3, in particular from 1.0 to 1.1. It turned out that a threshold lying in the beforementioned range is particularly appropriate for the present application. A threshold of 0.2 corresponds to 20 % deviation between the mean left ventricular interval and the mean right ventricular interval. A threshold of 2.0 denotes a deviation of 200% between the mean left ventricular interval and the mean right ventricular interval. A deviation lying in a range of from 30 % to 100 % (i.e., from 0.3 to 1.0) is particularly appropriate.

[0038] In an embodiment, the computer-readable program causes the processor to store the latest 5 to 60 seconds, in particular the latest 10 to 55 seconds, in particular the latest 15 to 50 seconds, in particular the latest 20 to 45 seconds, in particular the latest 25 to 40 seconds, in particular the latest 30 to 40 seconds of the detected right ventricular electric signal and / or of the detected left ventricular electric signal before the first event has been detected that is used for calculating that mean right ventricular interval or for calculating that mean left ventricular interval that caused the deviation between the mean right ventricular and the mean left ventricular interval being at least 20 % (i.e., being equal to or bigger than 0.2). Typically, such range of the detected cardiac electric signal is fully sufficient to evaluate by a subsequent analysis whether there is indeed an electrode integrity problem as assumed by the internal evaluation of the events of the cardiac electric signal.

[0039] In an embodiment, the computer-readable program causes the processor to store the next 1 to 10 seconds, in particular the next 2 to 9 seconds, in particular the next 3 to 8 seconds, in particular the next 4 to 7 seconds, in particular the next 5 to 6 seconds of the detected right ventricular electric signal and / or of the detected left ventricular electric signal after having detected a last event that was used for calculating that mean right ventricular interval or for calculating that mean left ventricular interval that caused the deviation between the mean right ventricular interval and the mean left ventricular interval being at least 20 % (i.e., being at least 0.2). Thus, in this embodiment, the implantable medical device does not only store the history of the event that was considered to be indicative for an electrode integrity problem, but also the post-history. This allows an even better subsequent evaluation of the cardiac electric signal and a distinction between an unusual course of the signal due to a physiologic reason and an unusual course of the signal due to the suspected electrode integrity problem.

[0040] In an embodiment, the implantable medical device does not only store the detected cardiac electric signal in the memory unit upon receiving the trigger signal upon recognizing a sufficiently high deviation between the mean right ventricular interval and the mean left ventricular interval, but also additional information such as marker time points and marker types. This additional information is stored, in an embodiment, in a data-reduced or compressed manner to save storing space and to reduce the power being necessary for storing, reading and / or transferring such additional data.

[0041] In an embodiment, the memory unit comprises a ring buffer for short-term caching the detected right ventricular electric signal and / or the detected left ventricular electric signal, as well as a long-term memory, wherein the storing of at least a part of the detected right ventricular electric signal and / or of the detected left ventricular electric signal comprises writing the part of the detected right ventricular electric signal and / or of the detected left ventricular electric signal to be stored from the ring buffer into the long-term memory. This guarantees that the stored part of the detected cardiac electric signal is available at a later time for evaluation remote from the implantable medical device. The long-term memory can be generally a volatile or a non-volatile memory. To reduce the risk of data loss, it is typically a non-volatile memory.

[0042] In an embodiment, the implantable medical device comprises a data communication unit that enables a data transfer of data stored within the memory unit to an external device or remote system. Such external device is, in an embodiment, a telemedicine system such as a home monitoring system. The data transferred from the implantable medical device to this remote system can then be evaluated on the remote system. To allow a better visualization for the medical staff engaged with the evaluation of the data, the events in the cardiac electric signals having suspicious features can be displayed in a highlighted manner.

[0043] In an embodiment, a data transfer takes place immediately after having stored the part of the cardiac electric signal into the memory unit. In an embodiment, the stored cardiac electric signal is transferred to the remote system upon the next opportunity to do so, i.e., upon confirmed contact with a transfer unit forming part of a data transfer network and / or being operatively coupled with the remote monitoring system.

[0044] In an embodiment, the data communication unit serves for transferring data to the remote system in a wireless manner. All standard data transmission protocols or specifications are appropriate for such a wireless data communication. Examples of standard data transmission protocols or specifications are the Medical Device Radiocommunications Service (MICS), the Bluetooth Low Energy (BLE) protocol, the Zigbee specification, the long range wide area network (LoRaWAN) protocol, the wireless personal area network (WPAN) specification, the low-power wide-area network (LPWAN) specification, the wireless local area network (WLAN) specification, the Global System for Mobile Communications (GSM) specification, the Long-Term Evolution (LTE) standard, and the fifth-generation technology standard for broadband cellular networks (5G). In an aspect, the present invention relates to a method of operating an implantable medical device for stimulating a human or animal heart, in particular an implantable medical device according to the preceding explanations. This method is characterized by the steps explained in the following.

[0045] In a first step, a right ventricular electric signal is detected with a first electrode of the implantable medical device. This is done, e.g., during a first time period. In this context, the detected right ventricular electric signal comprises a plurality of right ventricular events. An appropriate example of such a right ventricular electric signal is an intracardiac electrogram (IEGM).

[0046] Afterwards, a mean right ventricular interval is calculated within the implantable medical device from a predetermined number of at least some right ventricular events of the plurality of right ventricular events. The predeterminable number of at least some right ventricular events of the plurality of right ventricular events falls within a first time window.

[0047] In another method step, a left ventricular electric signal is detected with a second electrode of the implantable medical device. This is also done, e.g., during the first time period or during at least a part of the first time period that covers the first time window. In this context, the detected left ventricular electric signal comprises a plurality of left ventricular events. An appropriate example of such a left ventricular electric signal is an IEGM.

[0048] In another step, a mean left ventricular interval is calculated within the implantable medical device from a predetermined number of at least some left ventricular events of the plurality of left ventricular events. The predeterminable number of at least some left ventricular events of the plurality of left ventricular events falls within a second time window, wherein the second time window comprises the first time window. In an embodiment, the second time window is identical or essentially identical to the first time window.

[0049] Afterwards, it is determined whether the mean right ventricular interval and / or the mean left ventricular interval falls below a value lying in a range of from 200 ms to 2000 ms, in particular from 250 ms to 1900 ms, in particular from 300 ms to 1800 ms, in particular from 350 ms to 1700 ms, in particular from 400 ms to 1600 ms, in particular from 450 ms to 1500 ms, in particular from 500 ms to 1400 ms, in particular from 600 ms to 1300 ms, in particular from 700 ms to 1200 ms, in particular from 800 ms to 1100 ms, in particular from 900 ms to 1000 ms. If this is the case, an electrode integrity problem might exist. Therefore, the general possibility of triggering storing the detected cardiac electric signal is made available. If the mean right ventricular interval and / or the mean left ventricular interval exceeds the beforementioned value, it is rather unlikely that an electrode integrity problem exists. Therefore, in such a case, no possibility of triggering storing the detected cardiac electric signal is made possible. Rather, the method is then terminated.

[0050] In a further method step that is only performed if the mean right ventricular interval and / or the mean left ventricular interval falls below the value lying in the beforementioned range of from 200 ms to 2000 ms, a deviation is determined between the mean right ventricular interval and the mean left ventricular interval.

[0051] If this deviation between the mean right ventricular interval and the mean left ventricular interval is bigger than 20 %, storing at least a part of the detected cardiac electric signal in the memory unit is triggered in a further method step. If the deviation is smaller than 20 %, the method is terminated without triggering such storing. Triggering such storing allows a later evaluation of the stored part of the cardiac electric signal, i.e., a deeper analysis of the cardiac electric signal, e.g., outside the implantable medical device with a computer having more computing capacity and being less limited in terms of power consumption than the implantable medical device is.

[0052] All embodiments of the implantable medical device can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the described method. Likewise, all embodiments of the described method can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the implantable medical device. Further details of aspects of the present invention will be explained in the following making reference to exemplary embodiments and accompanying Figures. In the Figures:

[0053] Figure 1 A schematically shows a system comprising an implantable medical device;

[0054] Figure IB schematically shows different components of the implantable medical device of Figure 1A;

[0055] Figure 2A shows a first electric derivation obtained along a first sensing vector illustrated in Figure 1 A;

[0056] Figure 2B schematically shows a second electric derivation obtained along a second sensing vector illustrated in Figure 1 A;

[0057] Figure 3 shows a schematic flowchart of an embodiment of a method employed by an implantable medical device; and

[0058] Figure 4 is a schematic illustration of the stored parts of the detected cardiac electric signal.

[0059] Figure 1 A shows a system comprising a device for cardiac resynchronization therapy (CRT) 1 as example of an implantable medical device for stimulating the human or animal heart. The system further comprises a home monitoring system 2 serving as remote system. It is possible for the CRT device 1 to establish a wireless data communication with the home monitoring system 2.

[0060] The CRT device 1 comprises a housing 3 with a header 4 and a first electrode 5 connected to the header 4. The first electrode 5 comprises a first tip electrode pole 6 and a first ring electrode pole 7 that is proximally arranged from the first tip electrode pole 6. A first sensing vector 8 is defined from the first ring electrode pole 7 to the first tip electrode pole 6. Electric cardiac signals sensed between the first tip electrode pole 6 and first the ring electrode pole 7, i.e., along the first sensing vector 8, are directly recorded within a heart chamber, typically the right ventricle. Thus, the first electrode 5 is designed and arranged to sense right ventricular electric signals.

[0061] The CRT device 1 additionally comprises a second electrode 9 that is also connected to the header 4. The second electrode 9 comprises a second tip electrode pole 10 and a second ring electrode pole 11 that is proximally arranged from the second tip electrode pole 10. A second sensing vector 12 is defined from the second ring electrode pole 11 to the second tip electrode pole 10. Electric cardiac signals sensed between the second tip electrode pole 10 and the second ring electrode pole 11, i.e., along the second sensing vector 12, are also directly recorded within a heart chamber, typically the left ventricle. Thus, the second electrode 9 is designed and arranged to sense left ventricular electric signals.

[0062] Figure IB schematically illustrates individual components of the CRT device 1 that are comprised within the housing 3. In this and in all following Figures, similar elements will be denoted with the same numeral reference. The housing 3 houses a detection unit 31 (also referred to as sensing unit) that comprises an analog-to-digital converter, a bandpass filter, and an offset compensation. The detection unit 31 is operatively connected with a processor 32 that has access to a memory unit 33. The memory unit 33 serves for storing instructions for the processor 32 as well as data detected by the detection unit 31. The housing 3 further comprises an evaluation unit 34 that can also be part of the processor 32 and that serves for extracting features from the detected cardiac electric signal. The housing 3 further comprises a stimulation unit 35 that serves for stimulating the heart from which the detection unit 31 detects electric signals. The first electrode 5 along with its first tip electrode pole 6 and first ring electrode pole 7 as well as the second electrode 9 along with its second tip electrode 10 and second ring electrode 11 (confer Figure 1 A) form part of the detection unit 31 and of the stimulation unit 35. Additionally, the housing 3 comprises a data communication unit 36 that serves for data transfer to the home monitoring system 2 (confer Figure 1 A).

[0063] Figure 2A shows an electric derivation obtained along the first sensing vector 9 illustrated in Figure 1A. The sensing unit 31 (confer Figure IB) has detected five different events 13 and has assigned an event sensing signal 14 to each of these events 13. In this context, the individual event sensing signals 14 are placed at the beginning of each of the events 13. The electric derivation obtained along the first sensing vector 9 represents a right ventricular electric signal so that each of the events 13 is a right ventricular event. The right ventricular events 13 marked with the numbers 3, 4, and 5 are used to calculate a mean right ventricular interval 15 that is schematically illustrated in Figure 2A with a dashed box. It represents a mean temporal distance between the individual right ventricular events 13 that are used for calculating the mean right ventricular interval 15.

[0064] Figure 2B shows an electric derivation obtained during the same time period as the derivation shown in Figure 2A. However, the derivation of Figure 2B is obtained along the second sensing vector 12 and constitutes a left ventricular electric signal comprising five different left ventricular events 16. A left ventricular event sensing signal 17 has been assigned to each of the left ventricular events 16. The individual left ventricular event sensing signals 17 are placed at the beginning of each of the left ventricular events 16.

[0065] A mean left ventricular interval 18 is calculated from a predetermined number of left ventricular events 16. It represents a mean temporal distance between the individual left ventricular events 16 that are used for calculating the mean left ventricular interval 18. In Figure 2B, this mean left ventricular interval is schematically depicted with a dashed box like the mean right ventricular interval 15 in Figure 2A.

[0066] The left ventricular events 16 that are used for calculating the mean left ventricular interval 18 are chosen on the basis of the right ventricular events 13 that are used for calculating the mean right ventricular interval 15 (confer Figure 2A). For this purpose, a leading time interval 19 is added before the right ventricular sensing signal 14 of that right ventricular event 13 that constitutes the first of the right ventricular events 13 used for calculating the mean right ventricular interval 15. In addition, a trailing time interval 20 running after the right ventricular sensing signal 14 of the last right ventricular event 13 used for calculating the mean right interval 15 is determined (confer Figure 2A). The mean left ventricular interval 18 is then calculated from all left ventricular events 16 occurring from the beginning of the leading time interval 19 (first additional time interval) until the end of the trailing time interval 20 (second additional time interval). This results in a bigger time window for considering left ventricular events 16 for calculating the mean left ventricular interval 18 then the time window applied for considering the right ventricular events 13 for calculating the mean right ventricular interval 15. In the embodiment illustrated in Figure 2B, the bigger size of the time window used for calculating the mean left ventricular interval 18 has, however, no influence on the total number of left ventricular events 16 considered for calculating the mean left ventricular interval 18. Thus, even though the second time window is bigger than the first time window used for calculating the mean right ventricular interval 15, both the mean right ventricular interval 15 and the mean left ventricular interval 18 are calculated from three cardiac events, namely three right ventricular events 13 or three left ventricular intervals 16, respectively.

[0067] Figure 3 is a schematic flowchart of a method applied in an embodiment of the implantable medical device. In a first calculation step 301, a mean right ventricular interval is calculated from a predetermined number of previously detected right ventricular events. In a second calculation step 302, a mean left ventricular interval is calculated from a predetermined number of previously detected left ventricular events. In a first determination step 303, it is checked whether the mean right ventricular interval calculated in the first calculation step 301 or the mean left ventricular interval calculated and the second calculation step 302 is smaller than an upper limit. This upper limit is fed to the first determination step 303 by an upper limit provision step 304 and lies in a range of from 200 ms to 2000 ms.

[0068] If the mean right ventricular interval and the mean left ventricular interval are bigger than the upper limit (N), no trigger is set for storing the detected right ventricular electric signal or left ventricular electric signal in a final step 305. If, on the other hand, the result of the first determination step 303 is that the mean right ventricular interval or the mean left ventricular interval is smaller than the upper limit (Y), a second determination step 306 is carried out. In this second determination step 306, it is checked whether a deviation between the mean right ventricular interval and the mean left ventricular interval is bigger than a predetermined threshold. This predetermined threshold is provided to the second determination step 306 by a threshold provision step 307. In the embodiment of Figure 3, the threshold provided by the threshold provision step 307 is 20 %. If the deviation between the mean right ventricular interval and the mean left ventricular interval is below 20 % (N), the method ends at the final step 305, with no trigger to store the detected right ventricular signal or the detected left ventricular signal being released. If, on the other hand, the deviation between the mean right ventricular interval and the mean left ventricular interval is bigger than 20 % (Y), storing at least a part of the detected right ventricular electric signal and / or of at least a part of the detected left ventricular electric signal is triggered in a trigger step 308.

[0069] Figure 4 illustrates an embodiment of storing the detected cardiac electric signal. In this embodiment, both the history 21 and the post-history 22 around a part 23 of the detected cardiac electric signal comprising those right ventricular events 13 that are used for calculating the mean right ventricular interval 15 that caused triggering of storing of the cardiac electric signal, in this context, both the right ventricular electric signal comprising right ventricular events 13 (upper curve) and the left ventricular electric signal comprising left ventricular events 16 (lower curve) are stored. For better visualization purposes only, only some of the right ventricular events 13 and of the left ventricular events 16 are marked with the respective numeral reference sign.

[0070] Typically, the history 21 comprises 5 to 60 seconds of the cardiac electric signal, wherein the post-history 22 comprises 1 to 10 seconds of the cardiac electric signal. Such a part of the detected cardiac electric signal is typically sufficient to subsequently analyze the signal more thoroughly for an electrode integrity problem. This is typically done in the remote monitoring system 2 (confer Figure 1A) since this remote monitoring system 2 allows computationally more complex feature extractions and classifications from the stored cardiac electric signal than this is possible within the CRT device 1. Table of References

[0071] 1 Device for cardiac resynchronization therapy (CRT) 2 Home monitoring system

[0072] 3 Housing

[0073] 4 Header

[0074] 5 First electrode

[0075] 6 Tip electrode pole

[0076] 7 First ring electrode pole

[0077] 8 First sensing vector

[0078] 9 Second electrode

[0079] 10 Second tip electrode pole

[0080] 11 Second ring electrode pole

[0081] 12 Second sensing vector

[0082] 13 Right ventricular event

[0083] 14 Right ventricular event sensing signal

[0084] 15 Mean right ventricular interval

[0085] 16 Left ventricular event

[0086] 17 Left ventricular event sensing signal

[0087] 18 Mean left ventricular interval

[0088] 19 Leading time interval

[0089] 20 Trailing time interval

[0090] 21 History of the detected cardiac electric signal

[0091] 22 Post-history of the detected cardiac electric signal 23 Part of the detected cardiac electric signal

[0092] 31 Detection unit

[0093] 32 Processor

[0094] 33 Memory unit

[0095] 34 Evaluation unit

[0096] 35 Stimulation unit

[0097] 36 Data communication unit

[0098] 301 First calculation step Second calculation step First determination step Upper limit provision step Final step

[0099] Second determination step Threshold provision step Trigger step

Claims

Claims1. Implantable medical device (1) for stimulating a human or animal heart, comprising a processor (32), a memory unit (33), a stimulation unit (34) configured to stimulate a human or animal heart, and a detection unit (31) configured to detect an electric signal of the same heart, wherein the detection unit (31) comprises a first electrode (5) for detecting right ventricular electric signals and a second electrode (9) for detecting left ventricular electric signals, wherein the first electrode (5) comprises a first electrode pole (6) and a second electrode pole (7) and wherein the second electrode (9) comprises a third electrode pole (10) and a fourth electrode pole (11), characterizedin that the memory unit (33) comprises a computer-readable program that causes the processor (32) to perform the following steps when executed on the processor (32): a) detecting a right ventricular electric signal with the first electrode (5), the detected right ventricular electric signal comprising a plurality of right ventricular events (13);b) calculating a mean right ventricular interval (15) from a predeterminable number of at least some right ventricular events (13) of the plurality of right ventricular events (13), wherein the predeterminable number of at least some right ventricular events (13) of the plurality of right ventricular events (13) falls within a first time window;c) detecting a left ventricular electric signal with the second electrode (9), the detected left ventricular electric signal comprising a plurality of left ventricular events (16);d) calculating a mean left ventricular interval (18) from a predeterminable number of at least some left ventricular events (16) of the plurality of left ventricular events (16), wherein the predeterminable number of at least some left ventricular events (16) of the plurality of left ventricular events (16) falls within a second time window, wherein the second time window comprises at least the first time window;e) determining whether at least one of the mean right ventricular interval (15) and the mean left ventricular interval (18) falls below a value lying in a range of from 200 ms to 2000 ms;f) if at least one of the mean right ventricular interval (15) and the mean left ventricular interval (18) falls below the value lying in the range of from 200 ms to 2000 ms, determining a deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18);g) if the deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18) is bigger than a threshold, triggering a storing of at least a part of the detected right ventricular electric signal and / or of at least a part of the detected left ventricular electric signal in the memory unit (33) to allow a later evaluation of the stored part of the right ventricular electric signal and / or of the left ventricular electric signal.

2. Implantable medical device according to claim 1, characterized in thatthe predeterminable number of right ventricular events (13) used for calculating the mean right ventricular interval (15) lies in a range of from 5 to 17and / orthe predeterminable number of left ventricular events (16) used for calculating the mean left ventricular interval (18) lies in a range of from 5 to 17.

3. Implantable medical device according to any of the preceding claims, characterized in thatthe second time window comprises a first additional time interval (19) covering a range from 0.1 to 5 seconds prior to a first of the right ventricular events (13) used for calculating the mean right ventricular interval (15),and / orwherein the second time window comprises a second additional time interval (20) covering a range from 0.1 to 5 seconds after a last of the right ventricular events (13) used for calculating the mean right ventricular interval (15).

4. Implantable medical device according to any of the preceding claims, characterized in that the threshold lies in a range from 20% to 200%.

5. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to recalculate the mean right ventricular interval (15) and / or the mean left ventricular interval (18) with every newly detected right ventricular event (13).

6. Implantable medical device according to any of claims 1 to 4, characterized in that the computer-readable program causes the processor (32) to recalculate the mean right ventricular interval (15) and / or the mean left ventricular interval (18) after a predeterminable second time period has passed.

7. Implantable medical device according to claim 6, characterized in that the predeterminable second time period lies in a range of from 1 to 10 seconds.

8. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to calculate the deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18) by an equation that comprises i) a quotient between the mean right ventricular interval (15) and the mean left ventricular interval (18) or ii) a quotient between the mean left ventricular interval (18) and the mean right ventricular interval (15).

9. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to calculate the deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18) by the following equation (I): / MLVI\ 100 * > x (I)V1” MRVl)whereinML VI denotes the mean left ventricular interval (18),MR VI denotes the mean right ventricular interval (15),x denotes the threshold.

10. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to store the latest 5 to 60 seconds of the detected right ventricular electric signal and / or of the detected left ventricular electric signal prior to detecting a first ventricular event (13, 16) used for calculating that mean right ventricular interval (15) or for calculating that mean left ventricular interval (18) that caused the deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18) being at least 20 %.

11. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to store the next 1 to 10 seconds of the detected right ventricular electric signal and / or of the detected left ventricular electric signal after detecting a last ventricular event (13, 16) used for calculating that mean right ventricular interval (15) or for calculating that mean left ventricular interval (18) that caused the deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18) being at least 20 %.

12. Implantable medical device according to any of the preceding claims, characterized in that the memory unit (33) comprises i) a ring buffer for short-term caching the detected right ventricular electric signal and / or the detected left ventricular electric signal and ii) a long-term memory, wherein the storing of at least a part of the detected right ventricular electric signal and / or of the detected left ventricular electric signal comprises writing the part of the detected right ventricular electric signal and / or of the detected left ventricular electric signal to be stored into the long-term memory.

13. Method for operating an implantable medical device (1) for stimulating a human or animal heart, in particular an implantable medical device (1) according to any of the preceding claims, characterized by the following steps:a) detecting a right ventricular electric signal with a first electrode (5), the detected right ventricular electric signal comprising a plurality of right ventricular events (13);b) calculating a mean right ventricular interval (15) from a predeterminable number of at least some right ventricular events (13) of the plurality of right ventricular events (13), wherein the predeterminable number of at least some right ventricular events (13) of the plurality of right ventricular events (13) falls within a first time window;c) detecting a left ventricular electric signal with a second electrode (9), the detected left ventricular electric signal comprising a plurality of left ventricular events (16);d) calculating a mean left ventricular interval (18) from a predeterminable number of at least some left ventricular events (16) of the plurality of left ventricular events (16), wherein the predeterminable number of at least some left ventricular events (16) of the plurality of left ventricular events (16) falls within a second time window, wherein the second time window comprises at least the first time window;e) determining whether at least one of the mean right ventricular interval (15) and the mean left ventricular interval (18) falls below a value lying in a range of from 200 ms to 2000 ms;f) if at least one of the mean right ventricular interval (15) and the mean left ventricular interval (18) falls below the value lying in the range of from 200 ms to 2000 ms, determining a deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18);g) if the deviation between the mean right ventricular interval (15) and the mean left ventricular interval (18) is bigger than a threshold, triggering a storing of at least a part of the detected right ventricular electric signal and / or of at least a part of the detected left ventricular electric signal in a memory unit (33) of the implantable medical device (1) to allow a later evaluation of the stored part of the right ventricular electric signal and / or of the left ventricular electric signal.

14. Method according to claim 13, whereinthe second time window comprises a first additional time interval (19) covering a range from 0.1 to 5 seconds prior to a first of the right ventricular events (13) used for calculating the mean right ventricular interval (15),and / orwherein the second time window comprises a second additional time interval (20) covering a range from 0.1 to 5 seconds after a last of the right ventricular events (13) used for calculating the mean right ventricular interval (15).

15. The method according to claim 13 or 14, characterized in that the threshold lies in a range from 20% to 200%.

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