The Response of the Sinus Node to Premature Stimulation of the Atrium Studied with Microelectrodes in Isolated Atrial Preparations of the Rabbit Heart

Abstract

The effect of ectopic atrial beats on the natural pacemaker of the heart has been discussed among electrophysiologists since a long time (Engelmann, 1897; Cushny and Matthews, 1897; Wenckebach, 1903). The advent of the microelectrode technique made it possible to study the response of single sinoatrial pacemaker cells to premature atrial beats (Bonke et al., 1969 and 1971; Klein et al., 1973; Miller and Strauss, 1974). Recently, Strauss et al. (1973) suggested that the premature atrial stimulation technique may be used for indirect assessment of sinoatrial conduction time in man. This method takes advantage of the fact that the length of the atrial cycle following an ectopic beat, which occurs early enough to discharge the sinus node, is determined by the sum of: (1) retrograde conduction time of the premature impulse from the atrium to the pacemaker center in the sinus node, (2) postextrasystolic pacemaker cycle, and (3) antegrade conduction time from the pacemaker center to the atrium. If there occurs no pacemaker shift within the sinus node and if the rate of pacemaker discharge is not influenced by the premature beat, the difference between the postextrasystolic atrial interval and the basic atrial cycle can be attributed to the sum of retrograde and antegrade sinoatrial conduction time. If one further assumes that antegrade and retrograde sinoatrial conduction velocities are equal, half of this time will give a calculated value for unidirectional sinoatrial conduction time.