[Depression of sinus nodal automaticity during permanent atrial pacing for the determination of the sinoatrial conduction time (author's transl)].

In 36 patients sinoatrial conduction time (SACT) was calculated by the continuous-atrial-pacing technique, first described by Narula et al. (9). Using three different stimulation frequencies, it could be shown that the return cycles A2A3 and the postreturn cycles A3A4 both were linearly correlated with rising stimulation frequency. Thus, if the formula given by Narula et al. was used [SACT = (A2A3 - A1A1) : 2] the calculated SACT-values linearly rose, too, which was caused by a stimulation frequency dependent progressive depression of the sinus nodal automaticity. This interfering influence of sinus nodal depression could be corrected by applying a modified formula for calculation of the SACT, i.e. SACTM = (A2A3 - A3A4) : 2. Thus calculation of sinuatrial conduction time by the modified continuous-atrial-pacing technique represents a method widely applicable in routine electrophysiological testing.