Implantable medical device

Abstract

Implantable medical device comprising a sensing unit, a control unit, a memory, a communication unit, wherein - the sensor unit is set up to detect an atrial heart signal over a predefined period of time, wherein the heart signal has a multitude of successive atrial events which form a multitude of successive heart intervals, - the control unit is set up to determine the length of each heart interval and, if the intervention length falls below a certain threshold, to increment a mode switch counter, - the control unit is set up to record a cumulative mode-switch time over the predefined period, - the control unit is set up to determine, after the predefined time period has elapsed, a percentage of the cumulative mode-switch time normalized to the predefined time period and to store it in memory together with a value of the mode-switch counter, and - and the communication unit is set up to send the stored value of the mode switch counter and the stored percentage of the cumulative mode switch time or an alarm signal based thereon to an external device.

Description

[0001] The present invention relates to an implantable medical device, in particular a pacemaker, cardioverter defibrillator (ICD) or cardiac monitor.

[0002] Such implantable medical devices, i.e., implants with their own power supply, such as pacemakers and cardioverter-defibrillators (ICDs), may have a so-called mode-switch function (hereinafter abbreviated as MSW function or simply "MSW"). This function is intended to prevent the conduction of (paroxysmal) atrial tachycardias (AT) in the form of ventricular stimulation.

[0003] Activating the MSW function in a dual-chamber pacemaker or ICD can, for example, trigger the automatic switching of a P-synchronized Brady mode to an R-synchronized Brady mode when a specific criterion is met. These criteria or conditions can be adjusted by the clinician, usually through several programming parameters.

[0004] To activate the MSW function, for example, an X out of Y criterion (standard 5 out of 8) can be used to determine that at least X with a cycle length shorter than Z (375 ms, corresponding to 160 bpm) occurred within the past Y PP intervals. Z is referred to as the MSW intervention interval.

[0005] To exit, i.e., deactivate, the MSW function, X out of Y (default 5 out of 8) PP intervals must lie above the MSW intervention interval.

[0006] An MSW counter in the active implant sums all MSW activations. This daily MSW value can be used as a quantitative measure to determine the frequency of rapid atrial rhythms.

[0007] Especially for patients with paroxysmal atrial fibrillation, this may be the only indication of such a physiological situation in current implants.

[0008] Fig. Figure 4 shows a real rhythm example for illustration and demonstrates the incrementing of the MSW counter as well as MSW time intervals.

[0009] For better understanding, it should be added that the detection of fast atrial rhythms in known systems, in the form of AT detection, is intended to make longer-lasting atrial load scenarios visible. Therefore, a generally higher atrial detection zone (standard 200 bpm) is programmed here, and such atrial detection is only triggered when 36 out of 48 (currently fixed in the system) PP intervals fall within the atrial detection zone.

[0010] Under the following scenarios, the MSW function may switch between an activated and a deactivated state, a behavior known as "MSW toggle": - a physiological scenario with short, recurrent atrial non-sustained tachycardias, - in the presence of persistent AT close to the MSW intervention interval, - difficult conditions for atrial sensing: ◯ Control level, ◯ Artifacts, ◯ Crosstalk of ventricular signals (farfield oversensing).

[0011] The general aim is to avoid MSW toggling (with the exception of the first scenario, short, recurrent atrial non-sustained tachycardias).

[0012] However, the duration for which the MSW function was activated cannot be inferred from a specific reading of the MSW counter.

[0013] For example, an MSW counter daily value of 100 leaves open the question of whether this patient experienced many MSW toggles within a relatively short period on that day, or whether the implantable medical device had an activated MSW function for longer periods throughout the day, i.e., was in mode-switch (MSW).

[0014] The state of the art includes recording the number of MSWs per day and transmitting this daily value to a remote monitoring system. However, interpreting the MSW daily counter itself is limited without further information.

[0015] If unwanted MSW toggles are detected, they can be reduced under certain circumstances by adjusting the Brady parameters (intervention interval limit, mode switch “X out of Y” detection criterion, sensing parameters, such as farfield blank window lengths).

[0016] In the event of an undesirable MSW toggle occurrence being detected using the MSW daily counter, parameter adjustments must be made on a patient-specific basis. However, interpreting the MSW daily value as a metric for the physiological situation remains difficult if the MSW behavior has already been improved by prior optimization of the (sensing) parameters (in the sense of a reduction in the MSW daily counter value due to non-physiological events such as far-field oversensing).

[0017] Based on this, the invention aims to provide an implantable medical device, in particular a pacemaker, cardioverter defibrillator (ICD) or cardiac monitor, which at least partially reduces the aforementioned disadvantages.

[0018] This problem is solved by an implantable medical device, in particular a pacemaker or cardioverter-defibrillator (ICD) or cardiac monitor, with the features of claim 1. Advantageous embodiments of this inventive concept are described below.

[0019] According to claim 1, an implantable medical device is disclosed, comprising a sensing unit, a control unit, a memory unit, and a communication unit. The sensing unit is configured to detect an atrial heart signal over a predefined period, wherein the heart signal comprises a plurality of successive atrial events, which constitute a plurality of successive heart intervals. The control unit is configured to determine the length of each heart interval and, if the interval falls below a predefined intervention length, to increment a mode-switch counter. The control unit is further configured to record a cumulative mode-switch time.Furthermore, the control unit is configured to determine, after a predefined time period has elapsed, a percentage of the cumulative mode-switch time normalized to that predefined period and to store this value, along with a corresponding value from the mode-switch counter, in its memory. The communication unit is configured to send the stored mode-switch counter value and the stored percentage of the cumulative mode-switch time, or an alarm signal based on these values, to an external device. The predefined time period can be, for example, a daily interval, a 6- to 24-hour interval, or the duration of a specific episode. It is also possible to evaluate the percentage of the cumulative mode-switch time, for example, for an entire observation period (e.g., a daily interval) and additionally for a specific episode duration (see also below).

[0020] In particular, the implantable medical device is thus able to determine, in addition to the MSW counter, the proportion of time during which the intervention length was undershot.

[0021] The proposed metric, i.e., the second parameter representing a percentage of active MSW time relative to the specified duration (e.g., total observation period), provides a useful tool for interpreting the MSW counter. Furthermore, it offers a potential trigger for alerting a clinical supervisor regarding suboptimal atrial sensing settings.

[0022] According to one embodiment, the intervention length is considered to be undershot if the lengths of 5 heart intervals within 8 consecutively recorded heart intervals are shorter than the intervention length. This undershot condition persists until the lengths of 5 heart intervals within 8 consecutively recorded heart intervals are longer than the intervention length. A mode-switch period runs as long as the undershot condition persists. Over the predefined time period, the mode-switch periods can accumulate to form a cumulative mode-switch time if the intervention length is undershot multiple times. If the intervention length is undershot only once during the predefined time period, the mode-switch period corresponds to the cumulative mode-switch time.

[0023] In the following, embodiments of the invention, as well as further features and advantages of the invention, will be explained with reference to the figures. The figures show: Fig. 1 an embodiment of an active implant, Fig. 2 another embodiment of an active implant, Fig. 3 another embodiment of an active implant, Fig. 4. An example of a detected heart rhythm with incrementing of the MSW counter and display of the MSW time intervals. Fig. 5. Using an example, the distribution of the “active_ms_percentage” of episodes of a test dataset with modewswitch_cnt == 1, where the number of relevant episodes is shown on the Y-axis (“Count”) over the percentage of the cumulative mode-switch time (“active_ms_percentage”) on the X-axis, Fig. 6. Using another example, the distribution of the “active ms_percentage” of episodes of a test dataset with modewswitch_cnt == 2, where the number of relevant episodes is plotted on the Y-axis (“Count”) over the percentage of the cumulative mode-switch time (“active_ms_percentage”) on the X-axis, and Fig. 7. Using another example, the distribution of the “active ms_percentage” of episodes of a test dataset with modewswitch_cnt == 3, where the number of relevant episodes is plotted on the Y-axis (“Count”) over the percentage of the cumulative mode-switch time (“active_ms_percentage”) on the X-axis,

[0024] To aid in the interpretation of the current value of an MSW counter, the present invention proposes, in particular, an additional parameter, namely a cumulative time (cumulative mode-switch time), which sums the time intervals (mode-switch time periods) in which the intervention length is less than the measured heart interval lengths. From this parameter, a percentage of the cumulative time (the percentage of the cumulative mode-switch time normalized to the predefined time period) can then be calculated as the quotient of the cumulative mode-switch time and the predefined time period (total observation period). The percentage of the cumulative mode-switch time provides an indication of the relative proportion of the total observation period in which the intervention length is less than the target. This provides the physician with additional information for optimizing relevant AT parameters.

[0025] A high MSW counter value combined with a low percentage of cumulative mode-switch time may indicate the need to increase the AT detection sensitivity (e.g., by choosing a lower "X out of Y" counter or reducing the AT interval threshold). Fig. Figures 5 to 7 provide a clear example in this regard.

[0026] The Fig. Figures 1 to 3 show exemplary embodiments of implantable medical devices according to the invention 210.

[0027] The in Fig. The implantable medical device 210 shown is an atrial pacemaker. This is connected to an atrial electrode 220 with at least two electrode poles 221, 222. The electrode 220 can be positioned in the right atrium. Voltage signals can be derived in the implant 210 via the vector 223, which spans between the electrode poles (RA-tip) 221 and (RA-ring) 222, and transmitted through an analog-to-digital converter as part of the sensing unit 212.

[0028] In the digitized signal, sense events of atrial cardiac events can be generated, which can be used in the control unit 213 to initiate the delivery of atrial stimuli by the generator 214 via electrode poles 221 and 222, if necessary. The control unit 213 is configured to calculate the cumulative mean square wave (MSW) time and percentage described herein, which can be stored in a memory 211 of the implant 210 at the end of a total observation period and transmitted via the communication unit 215 to a communication unit 301 of an external programmer 300. The MSW function itself, i.e., the switching from a P-synchronized mode to an R-synchronized mode, is not implemented here, as this is a single-chamber pacemaker.Rather, the value of the MSW counter and the percentage of MSW time serve here as diagnostic parameters for the early detection of atrial tachycardia.

[0029] The parameterization of the components of the implant 210 can be carried out by the external programming device 300, which exchanges information with the communication unit 215 of the implant 210 via the communication unit 301.

[0030] The one in Fig. The embodiment shown in Figure 2 depicts a dual-chamber pacemaker. Here, the implant 210, in addition to the embodiment shown in Figure 2, features a dual-chamber pacemaker. Fig. 1. A ventricular electrode 230 with at least two electrode poles 231, 232 is provided. The electrode 230 can be positioned in the right ventricle. The generator 214 can deliver stimuli to the ventricle via the additional vector 233, which spans between the electrode poles (RV tip) 231 and (RV ring) 232.

[0031] The in Fig. The embodiment shown in Figure 3 also depicts a dual-chamber pacemaker connected to an electrode lead 220 that can be anchored in the ventricle. The electrode lead 220 has two atrial electrode poles 221 and 222 and two ventricular electrode poles. The atrial electrode poles 221 and 222 differ from the embodiments according to Figure 3. Fig. 1 and Fig. The 2 electrodes can be positioned suspended in the atrium. Atrial signals can be recorded via vector 223, which spans between electrode poles (RA-Tip) 221 and (RA-Ring) 222. Stimuli can be delivered to the ventricle via generator 214 via a further vector 23l, which spans between electrode poles (RV-Tip) 231 and (RV-Ring) 232.

[0032] In the sense of the MSW function described in the introduction, the embodiments according to Fig. 2 and Fig. Option 3 is preferred, insofar as it explicitly provides for stimulus delivery in the ventricle in addition to perception in the atrium. However, based on examples 3 to 5 presented below, a system that focuses solely on the atrium and specifically includes appropriate alarm notifications is also useful (see below).

[0033] The Fig. Figure 4 shows a short segment of an episode from a dual-chamber ICD system. From top to bottom, the events detected by the device are shown first, followed by the signal waveforms in leads "FF" (far field), "A" (right atrium), and "RV" (right ventricle). The incrementing of the MSW counter ("count += 1") and the MSW time intervals ("mode switch active") are also indicated for illustration. Example 1 (daily “active MSW percentage” as a diagnostic parameter)

[0034] According to an example of the invention, the percentage of MSW time ("active MSW percentage") is based on the daily interval, i.e., determined for the past 24 hours and sent to a remote monitoring system. A corresponding trend can be added as an additional diagnostic option to both the remote monitoring system and the programming device 300. Example 2 (episode-based “active MSW percentage” as a diagnostic parameter)

[0035] According to another example of the invention, the percentage of MSW time ("active MSW percentage") for each episode is additionally determined during each AT detection. This is done by calculating the ratio of the MSW time to the episode duration.

[0036] For current episodes, i.e., those that are still running beyond the total observation period, the percentage of MSW time ("active MSW percentage") can be determined at least until the interruption and the episode duration reached up to that point, and appended as information in the episode details. Example 3 (automated alerting upon detection of a potentially long-lasting AT just below the AT detection limit)

[0037] An alert will be triggered (during the next follow-up on the programming device 300 or in the remote monitoring system) if an issue arises within the last observed day. a. no AT episode recording has occurred b. and the percentage of MSW time (“active MSW percentage”) is between X1 and X2% (parameterizable). c. and the value of the MSW counter is below X3. Example 4 (automated alerting in case of potential atrial undersensing)

[0038] An alert is triggered (during the next follow-up on the programming device 300 or in the remote monitoring system) if, within an AT episode: a. the percentage of MSW time (“active MSW percentage”) is above X1 Example 5 (“pre AT detection” also in implantable cardiac monitors or loop recorders)

[0039] Another embodiment of the invention involves implantable medical devices without a stimulation function, such as an implantable cardiac monitor (ICM). The percentage of mean square wave (MSW) time ("active MSW percentage") can be determined based on the monitored heart rhythm and, in particular, communicated automatically to the clinical staff, e.g., according to Examples 3 and 4. Furthermore, the relatively short MSW cycles (standard condition: 5 out of 8 atrial events are considered (MSW) tachycardic) could enable the active implant or ICM to easily detect paroxysmal atrial fibrillation (AF) based on the daily MSW counter value and the percentage of MSW time ("active MSW percentage").The core of the MSW function described in the introduction and originally used in dual-chamber pacemakers can thus serve here as a kind of "pre-trigger" for the actual AT detection.

[0040] The present invention proves to be advantageous because the proposed second (diagnostic) parameter (“active MSW percentage”) facilitates the interpretation of the MSW counter value.

[0041] The Fig. Figures 5 to 7 show the distribution of the active MSW percentage for different MSW counter values ​​(ms_cnt = 1, 2, 3) of individual episodes. The data are derived from simulations of the proposed diagnostic parameter on a representative dataset (N = 40,000 episodes). It can be seen that the distribution is not limited to a specific range of the active MSW percentage. Thus, the active MSW percentage metric provides an indication of which scenario underlie the respective mode switch in dual-chamber pacemakers.

[0042] The in the Fig. The information shown in sections 5 to 7 can be interpreted as follows (see in particular sections 5 to 7). Fig.6) that for episodes with two MSW switchings in dual-chamber pacemakers (ms_cnt = 2) there is both a significant proportion (albeit a smaller overall proportion) of cases in which the MSW was active for only a small proportion of the time (<50%) and cases in which the MSW was active for a predominant proportion of the time.

Claims

[1] Implantable medical device comprising a sensing unit, a control unit, a memory, a communication unit, wherein - the sensor unit is set up to detect an atrial heart signal over a predefined period of time, wherein the heart signal has a multitude of successive atrial events which form a multitude of successive heart intervals, - the control unit is set up to determine the length of each heart interval and, if the intervention length falls below a certain threshold, to increment a mode switch counter, - the control unit is set up to record a cumulative mode-switch time over the predefined period, - the control unit is set up to determine, after the predefined time period has elapsed, a percentage of the cumulative mode-switch time normalized to the predefined time period and to store it in memory together with a value of the mode-switch counter, and - and the communication unit is set up to send the stored value of the mode switch counter and the stored percentage of the cumulative mode switch time or an alarm signal based thereon to an external device.

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