Cardiac electrotherapy device for cardiac contraction measuremen

Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems

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128642, A61N 1362

Patent

active

056930747

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to cardiac pacemakers and implantable cardioverters--defibrillators, more particularly to improved detection of pathologic tachycardias and fibrillation, as well as to more physiologic sensor for rate responsive pacing and accurate detection of pacing capture.


BACKGROUND AND PRIOR ART

Tachycardia is a condition in which the heart beats rapidly. Pathologic tachycardia is the one which disturbs the hemodynamics, causing the drop of systemic blood pressure. There are many types of pathologic tachycardias and the electrophysiology differentiates two major classes: supraventricular and ventricular tachycardias. Tachycardia is often the result of electrical feedback within the heart structures where the natural beat results in the feedback of an electrical stimulus which prematurely triggers another beat. There are several different cardiac pacing modes which may terminate the tachycardia. The underlying principle in all of them is that if a pacemaker stimulates the heart at least once shortly after a heartbeat, before the next naturally occurring heartbeat at the rapid rate, the interposed stimulated heartbeat disrupts the stability of the feedback loop thus reverting the tachycardia to sinus rhythm. Such a pacemaker was disclosed in the U.S. Pat. No. 3,942,534 which, following detection of tachycardia, generates a stimulus after a delay interval. The most hazardous arrhythmia is ventricular tachycardia which may progress in the lethal arrhythmia ventricular fibrillation. Because the ventricular tachycardia is not always successfully treated and terminated by antitachycardia pacing, the implantable cardioverter--defibrillator is used to deliver the high energy pulse shock in order to cause the cardioversion of ventricular tachycardia to sinus rhythm. Such an implantable device was disclosed in the U.S. Pat. No. 4,614,192 comprising a bipolar electrode for R-wave sensing, the system utilizing heart rate averaging and probability density function for fibrillation detection. The similar system for cardioversion is disclosed in the U.S. Pat. No. 4,768,512 which has the high frequency pulse delivery. All these systems deliver high energy shock through the special patch-electrodes such as described in the U.S. Pat. No. 4,291,707. In order to simplify the surgical procedure, systems comprising superior vena cava electrode and subcutaneous electrode, such as described in the U.S. Pat. No. 4,662,377, have been developed. The supraventricular tachycardia caused by atrial flutter or fibrillation can be also treated by implantable cardioverter such as described in the U.S. Pat. No. 4,572,191. The difficulty in the electrotherapy treatment of tachycardia is that the implantable apparatus has to comprise means for the accurate detection of pathologic tachycardia in order to deliver the electrotherapy pulses whenever the pathologic tachycardia occurs. The problem is that the heart rhythm increases its frequency physiologically whenever either the physical or the emotional stress occurs. The means for pathologic tachycardia detection must accurately differentiate the natural sinus tachycardia which may not be treated by means of electrotherapy from the pathologic tachycardia which has to be treated. Therefore the discrimination between normal and pathologic tachycardia on the basis of frequency measurement is not reliable. In order to overcome this problem numerous methods of tachycardia detection have been developed which are applicable in the implantable electrotherapy devices.
Such a system has been disclosed in the U.S. Pat. No. 4,475,551 where the heart rate sensing as well as probability density function were used to distinguish between ventricular fibrillation and high rate tachycardia. More sophisticated system has been disclosed in the U.S. Pat. No. 4,790,317 which can automatically recognize the pathologic rhythm by means of monitoring of the pulse sequence representing the ventricular electrical activity. At least two sensing positions i.e. to each ventricular epicar

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