[Secondary pauses in sinus node dysfunction].

Frequency and importance of secondary pauses (SP) following termination of high rate artrial pacing were evaluated in 64 patients. The maximal values of the first 10 post-pacing cycles, resulting from series of pacing between 70/min--160/min, were compared with the normal post-pacing values of Benditt. SP were present in 1 case (4%) of 23 patients without electrocardiographic signs of sinus node dysfunction (SDF), but in 21 cases (51%) of 41 patients with SDF (p less than 0.01). SP were more frequent in patients with SA-Block and/or sinus pauses (64%) and with bradycardia-tachycardia-syndrome (60%), whereas were more rare (35%) in patients with sinus bradycardia only. Patients with SDF and SP did not significantly differ from patients with SDF without SP concerning absolute and corrected sinus node recovery time, basal heart rate, reduction of cycle length after atropine, abnormal reactions to carotid sinus pressure and frequency of syncopes. In 1 patient SP, present in basal conditions, were not evident after atropine. SP could be interpreted as indication of SDF and should always be searched for because it may be the only evidence of SDF after atrial pacing; therefore SP may reduce the frequency of false negative tests after rapid atrial pacing. Possibly, vagal mechanisms are involved.