Incidence and electrophysiologic characteristics of supernormal atrial conduction in humans

Abstract

The incidence and electrophysiologic characteristics of supernormal atrial conduction (SNC) were examined by cardiac stimulation in 53 control subjects. Their ages ranged from 15 to 71 years (mean age, 50 ± 21 years) (mean ± SD). There were 27 women and 26 men in the study. Conduction of premature atrial responses from the sinus node to the atrioventricular node (intraatrial conduction time) was supernormal in 27 (51%) subjects and conduction to the left atrium (interatrial conduction time) was supernormal in 35 (66%) subjects (difference not significant). At coupling intervals ranging between 440 and 240 ms, the conduction time of the premature beats was as much as 25 ms shorter than that of the basic driven beats. The maximum decrease in interatrial conduction time during the period of SNC was 13 ± 5 ms and the maximum decrease in intraatrial conduction time was 9 ± 3 ms ( P < .001). The supernormal interatrial conduction zone was 71 ± 29 ms and the supernormal intraatrial conduction zone was 57 ± 25 ms ( P < .05). There was a significant positive correlation between the SNC zone and the maximum decrease in conduction time ( r = .82; P < .001). Supernormal atrial conduction was stable, reproducible, and remained constant in individual patients. Supernormal atrial conduction was found to be a relatively frequent phenomenon. There was a significantly greater SNC zone and maximum decrease in conduction time in interatrial conduction than in intraatrial conduction. Knowledge of the electrophysiologic characteristics and the incidence of SNC in control subjects should provide a better understanding of its role in the genesis of reentry when studied in patients with atrial flutter or paroxysmal atrial fibrillation.