Patterns of ventriculo-atrial conduction in the Wolff-Parkinson-White syndrome.

In 36 patients with the Wolff-Parkinson-White syndrome, ventriculo-atrial (VA) conduction was studied using the single test stimulus method. In 22 patients no significant change in VA conduction time occurred following test stimuli with increasing prematurity suggesting exclusive VA conduction by way of the accessory pathway, an accessory pathway with a shorter refractory period than the His-AV node pathway, or identical refractory periods in both pathways. In 14 patients showing this VA conduction pattern tachyeardias could be initiated by a single early ventricular premature beat. This finding lends credence to the hypothesis that the accessory pathway is an essential link in the tachycardia circuit. In two of the five patients showing exclusive VA conduction over the His-AV node pathway single re-entrant beats with antegrade conduction over the accessory pathway could be elicited by appropriately timed ventricular premature beats. In one patient showing this pattern a sustained tachycardia with AV conduction over the accessory pathway could be initiated. A total of eight patients did not show VA conduction over the