Overdrive suppression in diagnosis of sick sinus syndrome.

A criterion to determine the indication for pacemaker implantation in the sick sinus syndrome by overdrive suppression is proposed. Overdrive suppression was performed in 10 patients with the sick sinus syndrome (SSS) and another 10 patients with normal sinus rhythm (NSR) who served as controls. In the SSS group, 9 patients had complained of such severe symptoms as Adams-Stokes attack and/or congestive failure and were referred to our laboratory for pacemaker implantation. One other patient, an apparently robust young man (20 years old) referred for detailed cardiac examination, had no remarkable symptoms except for arrhythmias, but was found dead two months later. Atrial pacing for overdrive suppression was carried out at first at various rates ranging from 60 to 180 beats/min for 15 sec, and then at a rate of 100 beats/min for various durations ranging from 5 to 180 sec. After cessation of the atrial pacing, asystolic pauses were measured and the maximum (maximum pause) among the pauses obtained was used as a parameter indicating depression of cardiac automaticity. The maximum pause in the SSS group ranged from 5.6 to 9.0 sec (mean +/- SD = 7.0 +/- 1.2), WHILE THOSE IN THE NSR group ranged from 0.7 to 1.5 sec (mean +/- SD = 1.2 +/- 0.14). Therefore, the maximum pause was considered not only to reflect the severity of the symptoms necessitating pacemaker implantation in the 9 patients of the SSS group but to have warned us of sudder death in another patient. We concluded that overdrive suppression is useful as a supplementary challenge to determine indications for pacemaker implantation for the sick sinus syndrome, and that prolongation of the maximum pause beyond 5.0 sec is the critical level for pacemaker implantation.