A system for aborting the dual pathway tachycardias in a heart comprising the syndrome of paroxysmal supraventricular tachycardia (due generally to atrioventricular nodal reentry or atrioventricular reentry using an anomalous atrioventricular connection for retrograde conduction) by sensing cardiac impulses and, with respect to each sensed cardiac impulse, determining if such sensed cardiac impulse is an inciting cardiac impulse, a cardiac impulse which occurs at a time with respect to the last received cardiac impulse which falls within a predetermined echo zone and which will result in the initiation of a dual pathway tachycardia, and inducing an aborting cardiac impulse in response to a sensed inciting cardiac impulse in the cardiac muscle at a time within the predetermined aborting zone for aborting the initiation of the dual pathway tachycardia. The system also contemplates sensing cardiac impulses and delivering aborting electrical stimuli at a particular position on the cardiac muscle to allow more accurate recognition of inciting cardiac impulses and for more effectively delivering the aborting electrical stimulus, inducing the aborting cardiac impulse in sufficient time to abort the onset of dual pathway tachycardia.

An electrical pacer device which responds to cardiac demand so as to alter the cardiac output in a fashion to satisfy that demand. Changes in the fundamental period of the atrial electrical cycle are detected and averaged over a predetermined time interval and the resulting control signal is used to raise and lower the ventricular heart rate to increase and decrease the foresaid cardiac output. At the same time, means are provided for continuously driving the ventricular rate toward a predetermined lower rate (the at rest rate) on a time cycle which is significantly longer than the above-mentioned predetermined time interval.

Device for stimulating the heart comprises means for producing stimulating pulses at regular intervals and means responsive to spontaneous heart signals for controlling the transmission of said pulses to the heart in dependence upon the timing and magnitude of the spontaneous heart signals and/or the average intramyocardial pressure. In the absence of spontaneous heart signals, stimulating pulses are produced at predetermined intervals. When spontaneous heart signals occur, an adjustable waiting period is introduced in which to allow a second spontaneous signal instead of a stimulating pulse. The duration of the waiting period is varied as a function of the interval of time which separates two consecutive spontaneous detected signals (i.e., not separated by any artificially induced heart signal).

An electrical pacer device which responds to cardiac demand so as to alter the cardiac output in a fashion to satisfy that demand. Changes in the fundamental period of the atrial electrical cycle are detected and averaged over a predetermined time interval and the resulting control signal is used to raise and lower the ventricular heart rate to increase and decrease the aforesaid cardiac output. At the same time, means are provided for continuously driving the ventricular rate toward a predetermined lower rate (the at rest rate) on a time cycle which is significantly longer than the above-mentioned predetermined time interval.

A pacemaker has circuitry which allows the time between the detection of an atrial contraction and the provision of an electrical stimulus to cause a ventricular contraction to vary with the rate of the sensed atrial contractions. The circuitry includes a differential amplifier having a reference voltage applied to one input and a capacitor coupled to the second input. The capacitor is charged from the time the atrial contraction is sensed to the time the charge equals the reference voltage, at which time the electrical stimulus is provided and the capacitor is discharged between the time the electrical stimulus is provided and the next atrial contraction is sensed. As the heart rate increases, the time between the atrial contractions decreases, and thus the capacitor discharges for a shorter time, or in other words, to a larger voltage and the time required for the capacitor to recharge to the reference voltage becomes less.