Extracorporal control device for an implantable medical device

0001The invention relates to an extracorporeal device for use with an implantable medical device, in particular a pacemaker, defibrillator or cardioverter, according to the preamble of claim 1.

0002The construction of a modern medical device which can be adapted to the individual conditions of a patient by means of a programming device usually makes it possible to record signals from inside the body. On the one hand, these can be signals which are to be transmitted as pure as possible from the measurement site, or signals which influence the operating behavior of the implantable device. These signals are influenced by signal transmission means which are provided within the processing part of the implantable device and are connected upstream or downstream of the telemetry stage.

0003In a modern pacemaker, for example, the transmission of the electrical action potentials of the heart in the form of the intracardiac electrocardiogram to an extracorporeal device is provided for the purpose of evaluation and / or recording.

0004The action signals of the heart represented in the intracardiac EKG are recorded by an input filter provided for the normal operation of the pacemaker and then processed further. Due to the transmission properties of the input filter of the pacemaker, in particular due to the frequency response of the filter, the action signals of the heart are changed to a considerable extent, so that they do not allow a reliable diagnosis when evaluated in an EKG analysis device.

0005From DE-A-2 545 802 a heart signal discriminator is known which serves to suppress interference signals which are detected simultaneously with the heart action signal. The cardiac signal discriminator has means by which the detected signals are rectified and attenuated at the same time.

0006From EP-A-0 012 709 a digitally controlled amplitude control device for electrocardiographic signals is also known. The proposed control device has means which increase or decrease the transmission factor by one step each time a pulse signal (QRS complex) appears after comparing the signal amplitude with a threshold value.

0007The circuit arrangements known from the cited documents essentially relate to an adaptation of the amplitude of the intracardiac signals in order at least to limit the effectiveness of interference signals. This is necessary because the amplitude of these so-called artifacts often exceeds the cardiac useful signal by a hundred times.

0008DD-A-295 995 describes a circuit arrangement for eliminating cardiac pacemaker pulse components from ECG leads, with which (surface) ECG signals can be freed from pacemaker pulse components by suitable filtering at the output of the ECG amplifier.

0009DE-A-3 701 947 describes a method for acquiring a surface ECG, in which reliable processing of the cardiac action signals is also to be ensured for pacemaker wearers by reading out the operating parameters of the pacemaker by means of a wireless signal transmission device and then during processing of the surface ECG are taken into account.

0010US Pat. No. 5,421,830 describes a programming system for a pacemaker or cardioverter / defibrillator with means for recording and analyzing an intracardially recorded heart signal, in which, in addition to means for storing and reproducing the heart signals, a simulation of the response of the implanted device to it is also simulated is provided.

0011However, the previously known circuit arrangements do not solve the problem that the intracardiac EKG is falsified by the input filter of the pacemaker. It is therefore possible to transmit the intracardiac EKG to an extracorporeal control device for differentiated evaluation or storage via a telemetry transmitter. However, the diagnostic value of this intracardiac EKG as well as its usefulness for a possible simulation of the response of the pacemaker is greatly reduced by the signal-influencing effect of the input filter arranged in the pacemaker or possibly other transmission elements.

0012In addition, there is the problem with the known circuit arrangements that the intracardiac EKG downstream of the point at which it was tapped for delivery to the telemetry unit is further influenced by amplifiers and filters before the signal of a detector device, such as a threshold value detector, which is processed in this way is processed. or a processing unit is supplied. The signal available on the extracorporeal device therefore differs from the signal present in the pacemaker at the input of the detector or processing device, so that the evaluation of the telemetrically transmitted signal does not allow a reliable statement about the detection or processing behavior of the pacemaker.

0013The problems mentioned above also exist with regard to the external analysis of other body signals which are transmitted to the outside from a tap point in the processing channel in an implanted medical device, for example also signals which characterize the physical activity of a patient.

0014The invention is therefore based on the object of creating an extracorporeal device for use with an implantable electromedical device which enables the most genuine possible provision and possibly meaningful further processing of intracorporeally detected signals outside the body with regard to the function of the implanted device.

0015The object is achieved by a device with the features of claim 1.

0016The invention includes the technical teaching in the case of the extracorporeal device on the one hand to compensate for the signal influence caused by a transmission element located in front of the tapping point of the signal - for example the input filter of a pacemaker - in order to obtain an unadulterated signal, and on the other hand to compensate for the the implanted device between the signal tapping point and the actual detector or to simulate signal processing in the processing unit by means of amplifiers and filters in order to be able to simulate the entire detection behavior of the implanted device externally.

0017The term “input signal” is to be understood in the following in a general sense: the invention is particularly advantageously applicable to natural (spontaneous) cardiac action signals, ie for the external processing of intracardiac EKGs. However, the application of the invention is also advantageously possible with body signals that reflect the activity of the pacemaker wearer, such as, for example, intrathoracically or intracardially detected impedance signals. However, it is not limited to this, but can in principle be used for all signals transmitted to the outside from the internal processing channel of an implanted device.

0018In the case of a pacemaker, the first transmission element arranged in the input channel is generally an input filter, which is designed, for example, as an anti-aliasing filter.

0019The second transmission element usually consists of an amplifier with programmable gain, which, by adjusting the gain, enables the signal detector to be adapted to the electrical level of the input signal, or a correspondingly programmable amplifier filter module.

0020The transmission elements can also consist of several individual components.

0021Pacemakers, with which versions of the device according to the invention can advantageously be used, have a telemetry transmitter for transmitting the body signal (especially inracardial ECGs) to the outside of the body, which is connected to the processing channel before the second transmission element and / or after the first transmission element. As a rule, this telemetry transmitter is part of a telemetry unit of the pacemaker, which allows both transmitting and receiving mode, the signals recorded by the pacemaker being transmitted in the transmitting mode, while the receiving mode allows the pacemaker to be programmed by the extracorporeal control device.

0022If the pacemaker has only one transmission element, the signal is tapped for the telemetry transmitter either upstream or downstream of this transmission element.

0023If, on the other hand, the pacemaker has two or more transmission elements (which is the rule in practice), the signal is tapped between the transmission elements.

0024The device according to the invention has, in an embodiment tailored to implanted devices with signal tapping after a transmission element, downstream of the telemetry receiver, a third transmission element, which has the task of compensating for the signal influence by the first transmission element upstream of the telemetry transmitter - as a rule the input filter. to provide the unadulterated input signal. This is particularly advantageous when recording and transmitting an intracardiac EKG as an input signal, since an unadulterated ECG has a much greater diagnostic value for the attending physician than the EKG signals determined by known control devices and distorted by the input filter of the pacemaker. The third transmission element therefore has, in particular, an exactly inverse transmission function with respect to the first transmission element, in order to be able to compensate for its signal-influencing effect as completely as possible.

0025For example, the first transfer link in the pacemaker has the complex transfer function <i><u>c</u></i>_{<i><u>1</u></i>}<i>(f)</i> on, the telemetry signal is calculated <i><u>TS</u>(f)</i> from the input signal <i><u>IT</u>(f)</i> according to the formula:<maths id="math0001" num=""><math display="block"><mrow><munder accentunder="true"><mrow><mtext mathvariant="italic">TS</mtext></mrow><mo>̲</mo></munder><mtext mathvariant="italic">(f) = </mtext><munder accentunder="true"><mrow><mtext mathvariant="italic">c</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext mathvariant="italic">1</mtext></mrow></msub><mtext mathvariant="italic">(f)</mtext><munder accentunder="true"><mrow><mtext mathvariant="italic">IT</mtext></mrow><mo>̲</mo></munder><mtext mathvariant="italic">(f)</mtext></mrow></math><img file="EP0783902A2_D0001.tif" /></maths>

0026The output signal <i><u>AS</u>(f)</i> of the third transfer element with the complex transfer function <i><u>c</u></i>_<i>3</i><i>(f)</i> is then calculated from the telemetry signal <i><u>TS</u>(f)</i>:<maths id="math0002" num=""><math display="block"><mrow><munder accentunder="true"><mrow><mtext mathvariant="italic">AS</mtext></mrow><mo>̲</mo></munder><mtext mathvariant="italic">(f) = </mtext><munder accentunder="true"><mrow><mtext mathvariant="italic">c</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext mathvariant="italic">3</mtext></mrow></msub><mtext mathvariant="italic">(f)</mtext><munder accentunder="true"><mrow><mtext mathvariant="italic">TS</mtext></mrow><mo>̲</mo></munder><mtext mathvariant="italic">(f)</mtext></mrow></math><img file="EP0783902A2_D0002.tif" /></maths>

0027The transfer function <i><u>c</u></i>_<i>3</i><i>(f)</i> must be selected so that the output signal <i><u>TS</u>(f)</i> of the third transmission element reproduces the input signal as pristine as possible. This leads to the requirement:<maths id="math0003" num=""><math display="block"><mrow><munder accentunder="true"><mrow><mtext mathvariant="italic">c</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext mathvariant="italic">3</mtext></mrow></msub><mtext mathvariant="italic">(f)</mtext><mtext> = </mtext><mtext mathvariant="italic">1 / </mtext><munder accentunder="true"><mrow><mtext mathvariant="italic">c</mtext></mrow><mo>̲</mo></munder><msub><mrow><mtext>​</mtext></mrow><mrow><mtext mathvariant="italic">1</mtext></mrow></msub><mtext mathvariant="italic">(f)</mtext></mrow></math><img file="EP0783902A2_D0003.tif" /></maths>

0028In implanted devices with signal tapping in front of further transmission elements, the signal appearing at the output of the transmission elements provided downstream from the tapping point (subsumed here as "second transmission element") differs from the telemetrically transmitted signal. Modeling of the pacemaker behavior is nevertheless made possible in that the transfer function of this element is also applied to the signal present there in the external device in accordance with one aspect of the invention. The externally arranged third transmission element (this term may also be used here. several transmission elements provided in the extracorporeal device) therefore has in this variant of the invention in particular exactly the same transmission function as the second transmission element arranged behind the telemetry transmitter.

0029In a practically particularly important development of this variant, the provision of means for setting different transfer functions of the third transfer link enables the pacemaker behavior to be modeled for different settings of the second transfer link without having to reprogram the pacemaker itself.

0030As already explained above, the second transmission element arranged in the cardiac pacemaker generally has a programmable amplifier which enables the downstream detector or processing device to be adapted to the level of the cardiac signals detected. This is important because the level of the cardiac signals sensed by the pacemaker depends on the position of the electrodes, the resistance of the body tissue and other factors and is therefore subject to fluctuations which have to be taken into account by adjusting the input gain.

0031In the case of previously known pacemaker systems, this setting is usually made by the attending physician programming various input gains in succession and judging on the basis of sense markers or on the basis of the pacemaker behavior whether the pacemaker recognizes a signal delivered by the heart or not (“sensing test”). The problem here is that the input gain settings made during the test already affect the pacemaker behavior, which is often undesirable during the test. If the input sensitivity is too high, interference signals are already incorrectly detected as heart actions, so that during the test there may be no stimulation per se. If, on the other hand, the input sensitivity is too low, the spontaneous cardiac actions are not detected and the pacemaker constantly stimulates during the test, even though the heart beats sufficiently fast.

0032Another disadvantage of the previously known pacemaker systems is that the doctor generally sets a higher input sensitivity when programming the pacemaker than is actually necessary in order to be able to reliably detect a cardiac event even in the event of fluctuations in the intensity of the cardiac signals. However, this leads to the pacemaker's input amplifier becoming saturated during a cardiac event with normal intensity, so that the amplitude of this cardiac event can no longer be determined.

0033In an advantageous variant of the invention, the third transmission element is therefore followed by a detector device which has essentially the same detection behavior as that of the pacemaker. The transmission behavior of the third transmission element can be adjusted in this case in order to determine the transmission function which enables an optimal detection behavior. Since the setting is made in the extracorporeal device and not - as in known pacemaker systems - in the pacemaker itself, the pacemaker behavior is not influenced during the test. Only after the optimal setting has been determined is this telemetrically transmitted and set by the external device to the programmable pacemaker. The third transmission element here preferably consists of a digital filter, the filter characteristics of which can be set by specifying a plurality of filter coefficients.

0034The extracorporeal device can be designed as a special control device for an implanted device (in particular a pacemaker, defibrillator and / or cardioverter), as a module of a programming device for such implanted devices or a body signal analysis device (such as an EKG or EEG device) or also be designed as an - in particular programmable - interface, Via which a conventional programming or analysis device can be connected to an implanted device in a substantially function-expanding manner.

0035Other advantageous developments of the invention are characterized in the subclaims or are shown in more detail below together with the description of the preferred embodiment of the invention with reference to the figures. Show it:<ul id="ul0001" list-style="none"><li>1 as a preferred embodiment of the invention, an extracorporeal control device for an implantable pacemaker as a block diagram,</li><li>Figure 2a shows an exemplary signal curve for the intracardiac cardiac signal processed in the pacemaker and</li><li>2b shows the corresponding signal in the extracorporeal control device according to FIG. 1 in digitized form.</li></ul>

0036The block diagram shown in FIG. 1 illustrates the structure of an extracorporeal control device 14 in cooperation with a programmable cardiac pacemaker 15. Only the modules related to the invention are shown of both devices; especially the conventional other components of a pacemaker are assumed to be known and are therefore not shown here.

0037The shown pacemaker 15 works according to the demand principle, ie it only emits stimulation pulses to the heart when the heart itself does not beat or does not beat sufficiently quickly. For the detection of cardiac signals, the pacemaker 15 therefore has an electrode E connected to the cardiac tissue H, which is connected to an anti-aliasing filter 1 for processing the input signal. In addition to the detection of spontaneous cardiac activity, this electrode serves to emit stimulation pulses and is therefore additionally connected to the output of a pulse generator 16.

0038The output signal of the anti-aliasing filter is fed to an amplifier 2, which amplifies the input signal by a factor of 32.

0039The amplifier 2 is a transmission element 3 with a plurality of filter elements 3a, 3b, 3c with adjustable cut-off frequencies <i>f</i>_<i>1</i>, <i>f</i>_<i>2</i>, <i>f</i>_<i>2</i> downstream, by setting the cutoff frequencies <i>f</i>_<i>1</i>, <i>f</i>_<i>2</i>, <i>f</i>_<i>3</i> an adaptation of the intracardially removed input signal to a downstream detector device 4 enables. In this way, interference signals can be filtered out, which are recorded together with the heart signals via the electrode. To set the filter characteristic, the transmission element 3 has a plurality of control inputs via which the cut-off frequencies of the individual filter elements 3a, 3b, 3c can be set.

0040The detector device 4 connected downstream of the transmission element 3 comprises as its main component a bipolar threshold value element which compares the amplified and filtered input signal with a positive and a negative threshold value and, in certain circumstances, detects a natural heartbeat when the positive threshold value is exceeded or the negative threshold value is undershot. The signal detector 4 additionally evaluates the temporal sequence and the duration of the threshold value violations in order to prevent incorrect detection when the signal level is shifted, for example due to an electrode shift in the body of the pacemaker wearer with the result that the threshold value is permanently exceeded or undershot.

0041If the detector device 4 detects a natural heartbeat in the manner described above, this leads to an inhibition of the pulse generator 16, which otherwise stimulates with a predetermined stimulation frequency (see below). This means that the pulse generator 16 resets its internal clock generator and thus only emits a stimulation pulse if no further natural heartbeat is detected within a predetermined period of time after the detection.

0042A body sensor S (shown here outside the heart) is used to determine the stimulation frequency according to the patient's current hemodynamic requirement (which can be implemented, for example, as an intrathoracically arranged impedance measuring probe in a manner known per se). Whose measurement signal is fed to an integrated amplifier and filter module 8, where signal processing takes place, and from there it arrives at a processing unit 9, which calculates the stimulation rate of the pacemaker and controls the pulse generator 16 accordingly, likewise in a known manner, from the processed body signal.

0043In addition to the conventional functioning described above as a rate-adaptive demand pacemaker, the pacemaker 15 enables the transmission of an intracardiac electrocardiogram (also referred to as "IECG") and the signals from the body sensor S to an extracorporeal control device 14.

0044Downstream of the anti-aliasing filter 1, a two-channel analog / digital converter 5 is therefore connected to the input channel, which first converts the filtered input signal from the pacemaker and the measurement signal from the body sensor S into a digital data word, which is followed by digital data transmission to the extracorporeal Control device 14 allows.

0045For this purpose, the pacemaker 15 has a telemetry unit 6.1, which enables both transmitting and receiving operation. In transmission mode, the IECG received via electrode E and / or the signal from body sensor S is transmitted to extracorporeal control device 14, while in reception mode, programming signals for setting the operating parameters of pacemaker 15 are received.

0046A programming option relates to the transfer function of the transfer element 3, which enables the detector device 4 to be adapted externally to the input signal received via the electrode by programming the desired transfer function.

0047Correspondingly, the extracorporeal control device 14 also has a telemetry unit 6.2, which enables the reception of the IECG and - in transmission mode - the programming of the pacemaker 15.

0048Furthermore, the extracorporeal control device 14 has a recursive digital filter system 10 of the second order, which enables filtering of the intracardiac EKG signal with a variable filter characteristic. In this case, the digital filter 10 calculates x as the sequence₁, x₂, ...., x_i, ... digital samples present intracardiac EKG signal as the output signal a sequence y₁, y₂, ..., y_i according to the formula<maths id="math0004" num=""><math display="block"><mrow><mtext mathvariant="italic">y</mtext><mtext>(</mtext><mtext mathvariant="italic">n</mtext><mtext>)=</mtext><apply><sum /><lowlimit><mtext mathvariant="italic">k</mtext><mtext>= l</mtext></lowlimit><uplimit><mtext mathvariant="italic">N</mtext></uplimit><mrow><msub><mrow><mtext mathvariant="italic">c</mtext></mrow><mrow><mtext mathvariant="italic">k</mtext></mrow></msub><mtext>·</mtext><mtext mathvariant="italic">y</mtext><mtext>(</mtext><mtext mathvariant="italic">n</mtext><mtext>-</mtext><mtext mathvariant="italic">k</mtext><mtext>)</mtext></mrow></apply><mtext>+</mtext><apply><sum /><lowlimit><mtext mathvariant="italic">k</mtext><mtext>=0</mtext></lowlimit><uplimit><mtext mathvariant="italic">M</mtext></uplimit><mrow><msub><mrow><mtext mathvariant="italic">c</mtext></mrow><mrow><mtext mathvariant="italic">N</mtext></mrow></msub><msub><mrow><mtext>​</mtext></mrow><mrow><mtext>+ l +</mtext><mtext mathvariant="italic">k</mtext></mrow></msub><mtext>·</mtext><mtext mathvariant="italic">x</mtext><mtext>(</mtext><mtext mathvariant="italic">n</mtext><mtext>-</mtext><mtext mathvariant="italic">k</mtext><mtext>)</mtext></mrow></apply><mtext>; </mtext><mtext mathvariant="italic">M</mtext><mtext>≤</mtext><mtext mathvariant="italic">N</mtext></mrow></math><img file="EP0783902A2_D0004.tif" /></maths>

0049The transfer function of this filter 10 is calculated as follows:<maths id="math0005" num=""><math display="block"><mrow><mtext mathvariant="italic">U</mtext><mtext>(</mtext><mtext mathvariant="italic">f</mtext><mtext>) = </mtext><msqrt><mfrac><mrow><msup><mfenced open="(" close=")"><mrow><apply><sum /><lowlimit><mtext mathvariant="italic">i</mtext><mtext>= l</mtext></lowlimit><uplimit><mtext mathvariant="italic">N</mtext></uplimit><mrow><msub><mrow><mtext mathvariant="italic">c</mtext></mrow><mrow><mtext mathvariant="italic">i</mtext></mrow></msub><mtext>· Cos (2 · π ·</mtext><mtext mathvariant="italic">f</mtext><mtext>·(</mtext><mtext mathvariant="italic">i</mtext><mtext>-1))</mtext></mrow></apply></mrow></mfenced><mn>2</mn></msup><mtext>+</mtext><msup><mfenced open="(" close=")"><mrow><apply><sum /><lowlimit><mtext mathvariant="italic">i</mtext><mtext>= l</mtext></lowlimit><uplimit><mtext mathvariant="italic">N</mtext></uplimit><mrow><msub><mrow><mtext mathvariant="italic">c</mtext></mrow><mrow><mtext mathvariant="italic">i</mtext></mrow></msub><mtext>· Sin (2 · sin (2 · π ·</mtext><mtext mathvariant="italic">f</mtext><mtext>·(</mtext><mtext mathvariant="italic">i</mtext><mtext>-1))</mtext></mrow></apply></mrow></mfenced><mn>2</mn></msup></mrow><mrow><mtext>1-</mtext><msup><mfenced open="(" close=")"><mrow><apply><sum /><lowlimit><mtext mathvariant="italic">i</mtext><mtext>=</mtext><mtext mathvariant="italic">N</mtext><mtext>+ l</mtext></lowlimit><uplimit><mtext mathvariant="italic">M</mtext></uplimit><mrow><msub><mrow><mtext mathvariant="italic">c</mtext></mrow><mrow><mtext mathvariant="italic">i</mtext></mrow></msub><mtext>· Cos (2 · π ·</mtext><mtext mathvariant="italic">f</mtext><mtext>·</mtext><mtext mathvariant="italic">i</mtext><mtext>)</mtext></mrow></apply></mrow></mfenced><mn>2</mn></msup><mtext>+</mtext><msup><mfenced open="(" close=")"><mrow><apply><sum /><lowlimit><mtext mathvariant="italic">i</mtext><mtext>=</mtext><mtext mathvariant="italic">N</mtext><mtext>+ l</mtext></lowlimit><uplimit><mtext mathvariant="italic">M</mtext></uplimit><mrow><msub><mrow><mtext mathvariant="italic">c</mtext></mrow><mrow><mtext mathvariant="italic">i</mtext></mrow></msub><mtext>· Sin (2 · π ·</mtext><mtext mathvariant="italic">f</mtext><mtext>·</mtext><mtext mathvariant="italic">i</mtext><mtext>)</mtext></mrow></apply></mrow></mfenced><mn>2</mn></msup></mrow></mfrac></msqrt></mrow></math><img file="EP0783902A2_D0005.tif" /></maths>

0050By setting the filter coefficients c_i the filter characteristics can be changed within wide limits.

0051The output signal of this digital filter 10 is supplied within the control device 14 to a detector or processing device 11 which has the same detection behavior as the detector device 4 located in the pacemaker 15. In this way, the detection behavior of the pacemaker 15 can be modeled for different filter characteristics without having to reprogram the pacemaker itself. For this purpose, the control device 14 has a control unit 13 into which the treating physician stores the filter coefficients c_i inputs and thus determines the filter characteristic of the digital filter 10. The control unit 13 programs these filter coefficients c_i then into the digital filter 10 so that the attending physician can use the output signal of the detector device 11 to assess the effects of the filter settings on the detection behavior of the pacemaker. As a means of checking the detection behavior, an indicator lamp 12 is shown in the figure, each of which indicates the detection of a cardiac action. In practice, of course, a refined preparation and also storage of the respective detection result will take place in order to be able to compare the effect of different filter settings.

0052In addition to the adjustable digital filter module 10, a filter and amplifier unit 17 is connected to the output of the second telemetry unit 6.2, to which the signal from the body sensor S (which is identified by coding in the transmission) is supplied by the telemetry unit. Their transmission curve corresponds to that of the assembly 8 in the pacemaker 15, so that the influence of the body (eg impedance) signal in its signal processing path can be simulated externally. A further display unit 18 is connected to the output of the filter and amplifier unit 17, on which the signal corresponding to the input signal of the processing unit 9 of the pacemaker can be displayed externally. Means for setting the transmission parameters of the assembly 8 are not shown in the figure, but can be provided and used in a similar manner to that described for the filter 10.

0053An exemplary signal curve for the output signal 19 of the digital filter 10 is shown in FIG. 2b. The threshold values ​​of the downstream threshold element 11 are represented by horizontal dashed lines 17.1, 17.2. With this signal course, the threshold value element 11 detects a cardiac event, since the lower threshold value 17.2 is not reached.

0054If the doctor has found the optimal filter characteristic in this way, the control unit 13 uses this to calculate which values ​​of the cutoff frequencies <i>f</i>_<i>1</i>, <i>f</i>_<i>2</i>, <i>f</i>_<i>3</i> are to be programmed so that the second transmission element 3 located in the pacemaker 15 optimally reproduces this previously determined filter characteristic.

0055The values ​​determined in this way are then transmitted from the telemetry unit 6.2 to a control unit 7 located in the pacemaker 15, which adjusts the three filter elements 3a, 3b, 3c accordingly, so that the pacemaker 15 exhibits optimal detection behavior. After programming these cutoff frequencies<i>f</i>_<i>1</i>, <i>f</i>_<i>2</i>, <i>f</i>_<i>3</i> the output signal of the second transmission element 3 then shows the course 18 shown in FIG. 2a, which, apart from the lack of discretization, corresponds to the course simulated by the extracorporeal control device 14 shown in FIG. 2b.

0056The embodiment of the invention is not limited to the preferred exemplary embodiments specified above. Rather, a number of variants are conceivable which make use of the solution shown even in the case of fundamentally different types.