Unusual re-entry mechanisms in patients with Wolff-Parkinson-White syndrome.

Three patients with the Wolff-Parkinson-White (WPW) syndrome were studied using His bundle recordings and programmed atrial stimulation. In two of them conduction of premature atrial depolarizations via the accessory pathway was possible when the His-Purkinje system was still refractory. The consequent conduction delay in the His-Purkinje system resulted in re-entry phenomena at the ventricular level in one case, and possibly also in another. In the third patient short runs of supraventricular tachycardia could be elicited, which were due to a longitudinal dissociation within the atrioventricular node. During these paroxysms, ventricular activation occurred over both the anomalous and the normal paths. The resulting QRS complexes resembledfusion beats as indicated by their configuration andpreceding Hpotentials. Supraventricular tachycardias in patients with the WPW syndrome are usually thought to result from re-entry mechanisms involving both the normal and the accessory pathways of atrioventricular conduc- tion. The increasing evidence favouring this mech- anism has been largely obtained by studying these arrhythmias using intracardiac electrographic tech- niques (Castillo and Castellanos, 1970; Narula, I973; Wellens, 1971).