The effect of atropine on ventriculoatrial conduction during ventricular pacing in patients with and without Wolff-Parkinson-White syndrome.

Electrophysiological studies were performed in five patients, two with the three without Wolff-Parkinson-White (WPW) syndrome. In the former patients group, the paroxysmal supraventricular tachycardia (PSVT) was concluded to reflect the circus movement utilizing the normal atrioventricular (A-V) conduction system for antegrade conduction and the Kent bundle for the retrograde conduction. Ventriculoatrial conduction time (VACT) was measured during ventricular pacing before and after the administration of atropine sulfate. In patients without WPW syndrome, the VACT prolonged and subsequently second degree ventriculoatrial block developed when the pacing rate was increased progressively and atropine facilitated the retrograde conduction, suggesting the ventriculoatrial conduction took place via the normal A-V pathway. In contrast, the VACT in patients with WPW syndrome remained unchanged during ventricular pacing at rates of 145/min and more before and after atropine, indicating the retrograde conduction was taking place through the Kent bundle. It is discussed that the analysis of the VACT before and after atropine serves as an aid to differentiate the underlying mechanisms of PSVT in patients with WPW syndrome.