The secondary poststimulative phase after rapid atrial pacing: its importance in the diagnosis of sinus node dysfunction.

The effect of atropine and the beta-blocker Tobanum was studied on intrinsic heart rate (IHR) and on rapid atrial pacing carried out before and after administration of the drugs. The primary and secondary postpacing parameters were examined in both circumstances. In patients with normal IHR, return to the basic heart frequency after the drugs showed an exponential characteristic while in patients with abnormal IHR, the cycles of PPC 2-10 have lost this characteristic feature. The latter was a more characteristic electrophysiological sign of sinus node dysfunction than the recovery time of the sinus node. In patients with abnormal IHR, maximum CPPC1 is sometimes normal.