Body activity controlled heart pacer

Abstract: A body activity sensor in a rate adaptive pacer responds to myoelectrical signals in the patient's electrocardiogram (ECG). These myoelectrical signals are a measure of body activity and thus control the pulse generation rate of the pacer. Preferably, the myoelectrical signals are obtained by filtering out high frequency portions from the ECG and processing these filtered frequency portions.

Description: The present invention relates to a body activity controlled heart pacer for pacing the heart of a patient, comprising pulse generating means for generating stimulation pulses at a basic rate, means for sensing myoelectrical signals, means for rectifying said myoelectrical signal, means for forming an average signal of said rectified signal, and controlling means for controlling said pulse generating means such that said basic rate is varied as a function of said average signal. Such a pacemaker is described in IEEE Engineering in Medicine and Biology Society first annual conference, Denver, 6th - 7th October 1979, IEEE, New York, W.A. Getzel et al "Variation of cardiac pacemaker rate relative to respiration" p. 50-52. The known pacemaker comprises sensing electrodes implanted in the diaphragm of a patient for sensing myoelectrical signals, a bandpass filter for filtering out signal frequencies characteristic of electromyogram signals, a rectifier and an integrator for forming an average signal of the rectified electromyogram signal, which average signal is related to the minute volume of respiration of the patient and used to control the pacing rate of the pacemaker. In EP-A-0 294 949, which is a prior application according to Art. 54(3) EPC, a body activity controlled heart pacer is described. The heart pacer senses, at intervals, an electrocardiogram of the heart of a patient. The electrocardiogram signal is filtered in a bandpass filter for obtaining a myopotential signal. The myopotential signal is used to control the pacing rate of the heart pacer. Myopotentials are a body activity signal, which once were considered to be undesirable noise signals since they could hinder - especially in the case of unipolar pacemakers - the correct detection of the QRS complex in the electrocardiogram. In the past extremely sophisticated detectors were required to discriminate between the QRS complexes and the myoelectrical signal components, which can sometimes reach amplitudes approaching 50 percent of the maximum QRS deflection. It is an object of the present invention to provide a body activity controlled heart pacer which monitors myoelectric activity for supplying a body activity signal without using additional sensors. According to the present invention, the above object is achieved in that for a heart pacer as defined at the beginning the means for sensing myoelectrical signals comprises means for sensing an electrocardiogram of the patient's heart and filter means for filtering out signal portions of the electrocardiogram, the frequencies of which are higher than the highest frequences characteristic of the electrocardiogram, whereby these filtered signals are used as myoelectric signals. Instead of attempting to supress the myopotentials in the electrocardiogram, the heart pacer utilizes these "noise signals" to control the frequency of the pulse generator. Also, using myopotentials to regulate the pulse generation frequency allows for a reduction in the sensitivity setting of the pacer's QRS detector, because it is no longer imperative to detect each and every QRS complex. In the event that the detector misses a QRS complex, the stimulation pulse supplied by the generator will not be detrimental, since it will in any case be generated at a frequency conforming to the activity level of the patient. The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings. Figure 1 is a schematic block diagram of a heart pacer controlled by a myoelectrical signal according to the principles of the present invention. Figure 2 is an electrocardiogram containing myoelectrical signals. In Figure 1 a heart pacer 1 comprises a stimulation pulse generator 2, which generates stimulation pulses at a basic rate. These stimulation pulses are transmitted to a patient's heart 3 through pacing lead 4 to a stimulation electrode 5 inserted in the heart 3. The stimulation electrode 5 together with the pacemaker housing (functioning as the counter electrode, not shown) also serves as a device for sensing the electrocardiogram (ECG) of the heart. The ECG is passed through amplifier 6 to both a QRS detector 7 and a high pass filter 8. The high pass filter 8 filters out signal portions of the ECG, the frequencies of which are higher than the highest frequencies characteristic of the ECG. The filtered portions are rectified by a rectifier 9 and the rectified portions are integrated by integrator 10 to form an average signal. The average signal is delivered to the input of a stimulation rate varying unit 11. This stimulation rate varying unit 11 alters the basic rate of the stimulation pulse generator 2 as a function of the average signal of integrator 10, which signal is a measure of body activity. Such a system could also be realized by using a comparator stage to pass only those high frequency signal components with amplitudes higher than a given preset threshold. After establishing the duration of these high amplitude signal portions, the stimulation rate varying unit 11 can use the resulting values to control the pulse generation frequency accordingly. A more advanced version of the system may include a QRS-detector containing a pattern-recognition circuit that identifies each QRS-complex. Such a circuit is described in U.S. Patent 4,516,579. The QRS detector 7 detects the occurrence of a QRS complex. Its output signal is supplied to an inhibition unit 12, the output signal of which controls the stimulation pulse generator 2 in the inhibition mode. In Figure 2 the QRS complexes in the ECG are generally designated with the reference numeral 13. The high frequency portions therebetween define the myoelectrical signals and are referenced by 14. The myopotentials 14 are influenced by various body activities, including arm movement and respiration. Some or all of these body activities reflected in the myoelectrical signals can be utilized to control the frequency of the stimulation pulse generator 2. For example, the ECG signal can be processed such that only those portions of the myoelectrical signal reflecting primarily the patient's respiration rate control the pulse generation frequency of the heart pacer 1.

Claims: A body activity controlled heart pacer (1) for pacing the heart (3) of a patient, comprising pulse generating means (2) for generating stimulation pulses at a basic rate, means (5, 6, 8) for sensing myoelectrical signals (14), means (9) for rectifying said myoelectrical signal (14), means (10) for forming an average signal of said rectified signal, and controlling means (11) for controlling said pulse generating means (2) such that said basic rate is varied as a function of said average signal, characterized in that the means (5, 6, 8) for sensing myoelectrical signals (14) comprises means for sensing an electrocardiogram (13) of the patient's heart and filter means (8) for filtering out signal portions of the electrocardiogram (14), the frequencies of which are higher than the highest frequencies characteristic of the electrocardiogram (13), whereby these filtered signal portions are used as myoelectric signals (14). The pacer according to claim 1, wherein the remaining portions of the electrocardiogram are supplied to a QRS detector (7) for inhibited stimulation.

Inventors: LEKHOLM ANDERS DR, LEKHOLM, ANDERS, DR.
Applicants: SIEMENS AG, SIEMENS ELEMA AB, SIEMENS AKTIENGESELLSCHAFT
Application year: 1988
Main classification: A61N1
IPC codes: A61N1