WO2006117112A1

WO2006117112A1 - Device and method for detecting signal recognition errors in an implantable cardiological appliance

Info

Publication number: WO2006117112A1
Application number: PCT/EP2006/003856
Authority: WO
Inventors: Ewald Himmrich; Philipp Nikolai
Original assignee: Johannes Gutenberg-Universität
Priority date: 2005-04-29
Filing date: 2006-04-26
Publication date: 2006-11-09
Also published as: DE102005019959A1

Abstract

The invention relates to an implantable cardiological appliance which comprises the option between an active and a passive mode. If at least one defined number of intervals between cardiac excitations detected in a defined interval falls below a set value, the cardiological appliance detects a cardiac dysrhythmia in the course of which an intracardiac electrocardiogram is established and the order of intervals between the detected cardiac excitations is measured and stored, the temporal uniformity of the intervals being continuously evaluated. In the passive mode, the cardiological appliance administers an antitachycardiac therapy to the muscle tissue in the event of a cardiac dysrhythmia and generates and stores an alert message if the intervals are not uniform. In the active mode, when a cardiac dysrhythmia occurs and the order of intervals between the detected cardiac excitations is not uniform, in addition to the generation and memorization of an alert message, application of an antitachycardiac therapy is delayed until either a defined uniformity of the order of intervals is detected or until a defined predetermined maximum duration for delaying the antitachycardiac therapy has elapsed.

Description

Apparatus and method for detecting signal detection defects in an implantable cardiology device

The invention relates to a device and a method for the detection of signal detection defects in an implantable cardiology device, in particular a device for the treatment of tachycardia cardiac arrhythmias, and a method for operating the same.

Implantable cardiology equipment for the treatment of rapid

Cardiac arrhythmias are a particular class of cardiac pacemakers capable of detecting tachycardiac arrhythmias through intracardiac probes and delivering different types of therapeutic pulses to myocardial tissue as an antitachycardic therapy. Such devices are commonly referred to as implantable cardioverter-defibrillators (ICDs), which devices are particularly useful for the prevention of sudden cardiac death.

Fast, life-threatening cardiac arrhythmias include ventricular flutter (VT) and ventricular fibrillation (VF). To detect such cardiac arrhythmias, an ICD, by means of special probes placed within the heart, misses electrical potentials that arise from mechanical cardiac actions, and thus can be regarded as a correlate of a mechanical heart stimulation. Conventional filters and amplifier systems can be used to process the signals thus obtained, so that at the end of the amplifier and filter chain a single heartbeat can be distinguished from further changes in potential, such as P-waves and T-waves. A common measure for determining a heartbeat is, for example, the measurement of the time sequence of the so-called R-waves of an intracardiac electrocardiogram (EGM), wherein the period between two cardiac excitations can be measured from the thus determined RR intervals. This results in a determination the heart rate as the reciprocal of the averaged intervals of successive cardiac excitations.

If an arrhythmia of the heart rate, in particular particularly high heart rates of more than 200 beats per minute or ventricular fibrillation occurs, an IDC device initiates a DC pulse on the myocardium to terminate such a tachycardic ventricular disorder, such a defibrillation pulse being both synchronous ie within a certain time frame of cardiac excitation, as well as unsynchronized with cardiac pacing, and its magnitude can be adjusted to the degree of arrhythmia. A gradual coordinated therapy is therefore possible depending on the severity of the present cardiac arrhythmia.

To detect the presence of a cardiac arrhythmia, in addition to the determination of a mean heart rate and the presence of a sudden onset and unnaturally increased heart rate as another method, the determination of the number of heart intervals, which are shorter than a certain predetermined decision value, a so-called "X from Y Such a detected cardiac arrhythmia initiates an operating phase in the IDC device, hereafter referred to as

Cardiac arrhythmia episode is described in which the preparations for the initiation of a therapeutic measure and its implementation are carried out. During such a cardiac arrhythmia episode, a digital intracardiac electrocardiogram may also be recorded, which may be read out by a telemetry transmission by the physician for the purpose of diagnosis.

In the known ICD devices, malfunctions may occur in which the presence of a tachycardic ventricular arrhythmia is falsely detected and a therapeutic intervention is applied, resulting in unnecessary pain and risk to the patient connected is. The causes of such erroneous detection can be divided into:

1. Malfunction of the ICD device, in particular the presence of a probe break.

2. Interfering myopotentials that can occur, for example, in diseases that lead to thin walls of the heart, such as dilated cardiomyopathy. In this case, the ICD device measures potentials that have no cardiac causes.

3. Occurrence of special intracardiac signals that do not represent a heartbeat (T or P waves).

4. Unphysiological, external signals, which are caused in particular by electromagnetic fields. This can be triggered by electrical devices, in particular by mobile radio systems.

The invention has for its object to provide an implantable cardiac device for the treatment of rapid cardiac arrhythmia, in particular an ICD device, which includes a device for detecting signal detection defects and a method for operating such a device, which in the case of a tachycardia ventricular actually present Cardiac arrhythmia with a high triggering safety initiates the application of therapeutic measures and at the same time excludes the presence of signal detection defects with the highest possible degree of security. Such an ICD device should be able to perform an analysis based on RR intervals of an intracardiac electrocardiogram for exclusion of signal detection defects and have a simple design with respect to the measurement and signal processing system used. The object underlying the invention is solved by the features of the independent claim.

The inventive method is based on the fact that tachycardia

Cardiac arrhythmias have a relatively stable pattern, i. the time intervals between two consecutive RR spikes are essentially uniform in the presence of a real cardiac arrhythmia. Compared to this, erroneously detected signals are characterized by a chaotic distribution so that the resulting detected sequence of time intervals between putative cardiac excitations undergoes greater temporal variation ,

An inventive ICD device or the operating method according to the invention first applies the known criteria for determining the presence of a tachycardic ventricular arrhythmia. This may, for example, be a determination of a heartbeat rate averaged over a particular time interval, or the use of the "X out of Y" method, i.e. the determination of a certain relative number of time intervals between two detected cardiac paces below a certain limit duration.

When these conditions are present, either an actual cardiac arrhythmia or an occurrence of signal detection defects may be the cause. To assess this question, the sequence of time intervals between the detected cardiac excitations are stored as from the initiation of a cardiac arrhythmia episode and these are examined for temporal irregularities. For each newly added measured value, the degree of uniformity of the present sequence of time intervals since the beginning of the cardiac arrhythmia episode is preferably redetermined. The more measured time intervals are available, the more certain is the statement about their uniformity. For the fastest and safest possible determination of

Uniformity, preference is given to the following methods or a combination of the following methods: 1. Determination of the standard deviations of the sequence of time intervals.

2. Determination of the relative number of time intervals which exceed a certain predetermined duration.

3. Determining the relative number of quotients of successive time intervals which exceed a predetermined maximum value or fall below a predetermined minimum value.

Each of the above-described measures may be used individually, with each time a corresponding computational step is performed, a numerical value follows for the uniformity of the present series of time intervals, which can be compared with a certain critical threshold for the uniformity. Particularly preferred is the use of a combination of the measures described above for uniformity calculation. Furthermore, it is also conceivable to carry out a weighted combination.

The necessary calculation and comparison steps can be from a

Microprocessor accessing an internal or external memory with all stored within the present cardiac arrhythmia episode intervals.

The above-described measures for the detection of

Signal detection defects are preferably carried out at least until the preparatory measures for initiating a therapeutic measure, in particular the charging of a capacitor for the application of a DC voltage shock, are completed. The longer the investigation of the temporal uniformity of the time intervals between the detected

Heart stimulation can be performed, the more certain can a statement whether an actual cardiac arrhythmia or only a signal detection defect is present.

By the measures described above for determining the uniformity in the sequence of the time intervals between the detected

Cardiac perturbations are determined by a value that is constantly refined with increasing duration for the check, which is referred to below as the uniformity factor. This uniformity factor can in turn be compared to a threshold based on a static evaluation. For this purpose, the stored time intervals and the associated intracardiac electrocardiograms for a multiplicity of cardiac arrhythmia episodes have been investigated by means of telemetric transmission and a distinction is made here between actual cardiac arrhythmias and signal recognition defects. Accordingly, the associated uniformity factors are calculated according to the measures described above, and from this a threshold value for the uniformity factor is determined. On the basis of these threshold values, a comparison between the determined uniformity factor and the stored threshold value can be carried out on entry into a cardiac arrhythmia episode by the ICD device and, depending on the result thus obtained, a warning in addition to the stored sequence of

Time intervals and the intracardiac electrocardiogram are included in the data on the corresponding history of cardiac arrhythmia. Such a warning can serve a doctor to recognize in an evaluation of the cardiac arrhythmia episode in question and specifically to search for possible causes. In particular, organic causes, which are triggered by a not necessarily cardiac disease, should be investigated.

Particularly preferred is an embodiment of the ICD device which has two modes, an active mode and a passive mode. In the passive

Mode, the comparison between the uniformity factor and the specified uniformity threshold is merely generated as a warning and stored. This can then serve, as described above, to adapt the threshold value to the individually present situation so as to carry out the most correct possible assessment of physiological artifacts. For example, signal detection defects that are due to interfering myopotentials may be different from patient to patient, so that an adjustment of the threshold for the uniformity of the time intervals of the detected cardiac excitations must be made.

On this basis, an improved detection of signal detection defects is possible, so that in the following can be switched from the passive mode to an active mode of the ICD device, which is preferably again carried out telemethsch. In the active mode, the comparison between the uniformity factor and the set threshold not only leads to a stored warning, but to a transmission of this information to the internal therapy decision tree for the application of a therapeutic measure. In general, this then leads to an intervention in the therapy function. This can range from a weakening of a therapeutic measure to a complete suppression of a therapy impulse. Furthermore, it is conceivable to delay only the therapy pulse further until the reliability of the statement, which is attributed to the uniformity factor, increases. Accordingly, the patient's safety increases before inappropriate shock delivery in active mode. At the same time, however, it is also necessary to preclude a misinterpretation by the detection system or the method for the signal detection defects. According to a preferred embodiment, therefore, in the event that the cardiac arrhythmia episode triggering condition is still present even after the expiration of a fixed maximum period of time, a therapy pulse is triggered even in a report of a suspected signal detection defect. Of course, it also comes to triggering such a therapy pulse, if for an originally displayed

Signal detection defect in the course of further monitoring of the Uniformity factor drops below the threshold and thus the reference to a signal detection defect is withdrawn.

The invention will be described in more detail below with reference to figures. In detail here is shown:

Fig. 1 shows the process sequence according to the invention in passive mode.

Fig. 2 shows the process sequence according to the invention in the active mode.

3 shows an illustration of an intracardiac electrocardiogram with rapid ventricular arrhythmia with the internally detected heartbeats indicated by arrows. The associated time intervals between the detected cardiac excitations are given in milliseconds.

FIG. 4 illustrates a representation corresponding to FIG. 1 in the case of the presence of signal detection defects.

Fig. 5 illustrates the determination of the uniformity factor based on a standard deviation.

FIG. 3 shows an intracardiac electrocardiogram which represents the occurrence of a ventricular fibrillation. In the present case, the RR intervals are correctly detected. Deviating from this, there is no tachycardiac arrhythmia in FIG. The ICD device, however, detects false signals and has therefore initiated a cardiac arrhythmia episode in the illustrated case. In the illustrated signal detection defect of this example, interfering signals of the diaphragm occurred without adequate cardiac excitation. According to FIG. 1, the method according to the invention is initiated by the detection of a cardiac arrhythmia episode. At first, it is not clear whether it is an actual tachycardiac arrhythmia or a signal detection defect. For the passive mode shown in FIG. 1, a therapeutic measure is immediately prepared and then applied without any time delay. At the same time, all detected heart intervals are stored within the cardiac arrhythmia episode and subjected to an evaluation in order to determine the uniformity factor in a subsequent method step. Shown is the application of three different methods for determining uniformity. These can be executed sequentially as shown. Also a parallel processing is conceivable. In modifications, only a single method of determining the uniformity factor can be used. It is also conceivable that the individual methods are weighted differently. As an example of such a method for determining the uniformity factor, the calculation of the standard deviation of the heart interval data shown in FIG. 3 may be performed.

FIG. 5 shows the schematic sequence of a preferred method for determining the uniformity factor. Based on all the time intervals between the detected cardiac excitations present within the cardiac arrhythmia episode, a standard deviation S is calculated. After each calculation, the currently existing value for the standard deviation S is compared with a threshold value E, so that after each recalculation a decision can be made between a correct and an erroneous detection of a cardiac arrhythmia.

Mathematically, the standard deviation is formed by the following formula:

V wn - \ s = standard deviation je = individual time interval between two detected cardiac excitations 3c = average of the time intervals between the detected cardiac excitations n = number of determined time intervals

According to the invention, the uniformity factor is determined in the passive mode for the stored heart interval data for the respective cardiac arrhythmia episode and, in the event of a signal defect, a uniformity factor is determined

Warning saved. As described above, a physician may then, as part of a therapeutic procedure, make an individual adaptation to the given physiological situation of a patient before the device is switched to an active mode.

FIG. 2 shows the active mode for the method according to the invention. In contrast to the passive mode, a therapeutic measure is not immediately initiated when a rapid cardiac arrhythmia in need of therapy is diagnosed. Instead, based on the stored data, the cardiac intervals of the ongoing cardiac arrhythmia episode are entered

Uniformity factor determined. This is in turn by one or a combination of the above-mentioned methods, for example, the calculation of a standard deviation and / or the determination of the relative number of time intervals, which describe a certain predetermined duration and / or the determination of the relative number of quotients each successive time intervals between the detected heartbeats, which exceed a predetermined maximum value or below a predetermined minimum value made. Furthermore, further methods are conceivable which serve to prove the temporal uniformity of the heart interval data. If, in the active mode, a signal recognition defect is assumed due to the established uniformity factor, then again different interventions on the therapeutic measure are assumed conceivable. In the simplest case, this is a time delay with the aim of obtaining even more reliable data on the temporal uniformity of heart intervals. In addition, a reduction of the therapeutic action or a phased application can be made. In addition, it is also conceivable to completely suppress a therapeutic measure. In FIG. 2, however, a maximum time specification for the suppression of a therapeutic measure is prescribed to ensure therapy safety. After a certain set time has elapsed, a therapeutic measure is also initiated when it is indicated that a signal detection defect exists.

In the active mode, in addition to the intervention on the therapeutic measure in accordance with the passive mode, a warning, which can be retrieved later by a doctor, stored together with the heart interval data of each cardiac arrhythmia episode.

In a more refined, not specifically illustrated embodiment, the different methods of determining the uniformity factor may be linked such that the decisions leading to the detection of a signal detection defect are "AND" linked while those

Decisions of the individual procedures indicating the presence of an actual rapid cardiac arrhythmia in need of therapy are "linked." That is, even the result of a method of determining the uniformity factor, which suggests that a situation in need of therapy is present, leads directly to the application of a therapeutic intervention ,

Claims

claims

An implantable cardiac device comprising

1.1 at least one intracardiac probe for measuring electrical potentials which are the correlate to mechanical cardiac excitations;

1.2 a device for detecting a heart excitation from the electrical potentials and a device for measuring the time intervals between the detected cardiac excitations and a device for storing and evaluating the time intervals; 1.3 a device for recording and storing an intracardiac electrocardiogram;

1.4 a choice between an active and a passive mode;

1.5 falls below at least a certain number of time intervals between detected cardiac excitations in a predetermined time interval a predetermined value, the cardiology device is a

Cardiac arrhythmia is detected, during which an intracardiac electrocardiogram and the sequence of time intervals between the detected cardiac excitations are measured and stored, whereby the temporal uniformity of the time intervals is continuously evaluated; 1.6 in passive mode, the cardiological device delivers an antitachycardic therapy to the muscle tissue in the event of a cardiac arrhythmia and, in the event of a non-uniform sequence of intervals, generates and stores a warning; 1.7 in the active mode, in the event of a cardiac arrhythmia and the presence of a non-uniform sequence of time intervals between the detected cardiac excitations, in addition to the generation and storage of a warning, the use of antitachycardic therapy is delayed until either a certain uniformity of the sequence of time intervals is detected or until a certain predetermined maximum period of time to delay the antitachycardic therapy expires.

2. Implanted cardiology device according to claim 1, characterized in that to evaluate the uniformity of the time intervals, the standard deviation of the sequence of the time intervals and / or the determination of the relative number of time intervals which exceed a certain predetermined duration and / or the determination of the relative number of quotients of each successive time intervals which exceed a predetermined maximum value or fall below a predetermined minimum value, is used.

3. Implantable cardiac device according to at least one of claims 1 or 2, characterized in that the degree of uniformity is compared with a threshold value.

4. Implantable cardiac device according to claim 3, characterized in that the threshold value is determined statistically.

5. Implantable cardiac device according to at least one of claims 3 or 4, characterized in that the threshold value can be changed telemetrically.

6. An implantable cardiac device according to at least one of claims 1 to 5, characterized in that the stored after the detection of a cardiac arrhythmia sequence of time intervals and the course of the intracardiac electrocardiogram and the warning when a non-uniform sequence of intervals can be read telemetrically.

7. An implantable cardiac device according to at least one of claims 1 to 6, characterized in that telemetrically between the active and the passive mode can be changed.

8. Implantable cardiological device according to at least one of

Claims 1 to 7, characterized in that the maximum time for delaying the antitachycardia therapy in the active mode in response to the occurring during a cardiac arrhythmia intervals of the detected cardiac excitations can be adjusted.