[Evaluation of sino-atrial function using the method of extrasystole induced by constant-relative premature impulses. 2. Application in 50 normal and abnormal studies].

The total immediate sino-atrial conduction time (SACT) as calculated by constant relative pacing, 40 or 50% of the immediate sinus cycle (SC), normally varies inversely with the SC. 50 patients were investigated by this method. In 38 patients without sino-atrial block (SAB) on the surface ECG, it was found that the mean slope of correlation between SACT and SC varied with the shape of the curve of Strauss and with the presence or absence of a post-pacing depression. The smallest slope was found in the group in which the curve of Strauss was horizontal in zone II, and in which there was no depression. In the groups with a rising zone II, comparative use of pacing with a fixed relationship in milliseconds suggested a phenomenon of decreasing retrograde conduction. In cases with sinus arrhythmia and a Strauss curve with scattered coordinates, the relationship between SACT and SC was maintained. 1st degree right-sided SAB should therefore be defined as a function of the immediate SC. In 12 other patients with SAB on the surface ECG, the immediate SACT was greatly lengthened so as to be immeasurable, and bore no relationship to the SC.