Double accessory pathways in Wolff-Parkinson-White syndrome.

Intracardiac electrophysiological studies were performed in two patients with Wolff-Parkinson-White (WPW) syndrome. Atrial pacing at increasing rates or shorter coupling intervals produced inscription of the forward His bundle deflection at progressively longer intervals after the onset of ventricular depolarization. There was an associated increase in QRS duration without any change in the P-R (or St-V) interval. This response was consistent with a Kent bundle. Case 1 also had a short A-H interval which did not show the expected prolongation with stimulation at progressively faster rates. This suggested the presence of a James bundle in addition to the Kent bundle. In case 2 beats conducted exclusively through the atrioventricular (A-V) node had a short H-V interval but a delta wave was not inscribed. Absence of an initial slurring was attributed to the existence of an infra-His bundle bypass of the Mahaim type causing only slight pre-excitation, which was not of sufficient magnitude to be recorded by body surface leads. However, the existence of a congenitally short anterosuperior division of the left bundle could nt be excluded.