Wolff-Parkinson-White syndrome with 1:2 atrioventricular conduction.

The QRS complex of the Wolff-Parkinson-White syndrome is thought to represent a fusion beat resulting from conduction over the normal pathway and an anomalous pathway. This report demonstrates utilization of both of these pathways resulting in two ventricular responses from a single supraventricular impulse. The presence of "1:2" atrioventricular conduction in this case firmly supports the fusion beat theory of the Wolff-Parkinson-White syndrome.