Automaticity of subsidiary pacemakers of patients with dysfunction of the sinus node.

Automaticity (postpacing impulse recovery time) of the sinus node or subsidiary pacemakers (or both) was determined by intracardiac recordings and atrial overdrive pacing in three patients with disease of the sinus node. Their electrocardiographic manifestations included sinus bradycardia, sinoatrial block, sinus arrest, atrioventricular junctional rhythm, and atrioventricular dissociation. One patient, who initially had syncope, demonstrated prolonged time for recovery of the sinus node (maximum corrected value, 3,485 msec) and impaired atrioventricular junctional automaticity (maximum corrected junctional recovery time, 1,460 msec). Of the remaining two patients without syncopal attacks, one had an adequate low atrial or junctional escape mechanism following cessation of pacing. The maximum low atrial escape interval was 1,660 msec, and the maximum junctional recovery time was 1,770 msec (corrected value, 140 msec). The third patient disclosed a prolonged maximum corrected recovery time for the sinus node (870 msec), while the maximum junctional recovery time was only 1,810 msec (corrected value, 160 msec). We conclude that automaticity of the subsidiary pacemakers in disease of the sinus node can be determined in the presence of atrioventricular dissociation or total sinus arrest, and that determination of the recovery time of the subsidiary pacemakers may be useful in identifying symptomatic patients with sinus nodal dysfunction.