Sinus node electrogram study on sinus pacemaker shifts.

The aim of this study was to investigate the sinus pacemaker shifts and its clinical significance. Spontaneous sinus pacemaker shifts and shifts after overdrive atrial pacing were assessed. A total of 43 cases, in whom stable sinus node electrograms (SNE) were obtained, were selected for the study, eight of the 43 cases had sick sinus syndrome (SSS group), the other 35 cases had no sinus node dysfunction (normal group). Sinus pacemaker shifts occurred spontaneously in 11.4% of the normal group and 12.5% of the SSS group respectively (P greater than 0.05); sinus pacemaker shifts were induced after overdrive atrial pacing in 25.7% of the normal group and 62.5% of the SSS group respectively (P less than 0.05). Sinus pacemaker shifts were characterized by loss or inversion of the primary positivity, with or without changes of P wave morphology on ECG, in association with significant prolongation of direct sinoatrial conduction time (SACTd) and sinus cycle length (SCL). The paper concludes: 1) the human sinus node has dominant and subsidiary foci; 2) after overdrive atrial pacing, sinus pacemaker shifts occur more frequently in patients with SSS than that in patients without SSS, which may be useful in evaluation of sinus node function.