[Sinus node electric activity in prolonged atrial pauses in subjects with the sick sinus syndrome]

Sinus node electrogram (SNE) was recorded in 15 patients with sick sinus syndrome (SSS) in which prolonged atrial pauses were observed. The aim of this study was clarify the physiopathological mechanisms underlying atrial pauses as well as to evaluate the sensitivity of sinoatrial conduction time (SACT) directly measured on SNE and of SACT estimated with the indirect Strauss method with respect to the detection of SSS. The following results were obtained: Sinus electrical activity was recorded during atrial pauses (greater than or equal to 2 basic sinus cycle length) in all the 9 patients in which the pauses spontaneously occurred and in the 2 patients in whom the pauses of 2860 and 3190 msec were induced by atrial pacing. In one of these latter two patients, moreover, a complete electrical desynchronization was observed. In the remaining 4 patients in whom, pauses (greater than or equal to 3 sec) were induced by carotid sinus massage of in 3 no sinus electrical activity was detected on SNE while in 1 advanced sinus node desynchronization was observed. Direct sinoatrial conduction time was abnormally prolonged in 6 patients with SSS and indirect sinoatrial conduction time in 9 patients.