Dual-chamber pacemaker with automatic selection of atrial refractory period

摘要

An improved atrial synchronous dual-chamber pacemaker provided with a variable refractory period during which the pacemaker is not responsive to sensed atrial contractions. The atrial refractory period is selected based upon whether the ventricular pacing pulse preceding the refractory occurred as a result of time out of the interval corresponding to the basic ventricular pacing rate, or due to time out of the A-V delay interval initiated in response to sensing of a natural atrial contraction. The pacemaker may most easily be practiced by modifying a DDD type pacemaker, and employing the V-A interval, normally separating an atrial pacing pulse from an immediately preceding ventricular contraction, as an extended atrial refractory period, employed only after generation of a ventricular pacing pulse not triggered by a preceding atrial contraction.