Analysis of re-entry mechanisms in the three patients with concealed Wolff-Parkinson-White syndrome.

Three patients with recurring attacks of supraventricular tachycardia and no electrocardiographic evidence of the Wolff-Parkinson-White syndrome (WPW syndrome) were studied using intracardiac recordings and atrial stimulation. The findings are interpreted as evidence of a concealed WPW syndrome. In all patients there was antegrade block of the anomalous atrioventricular (A-V) pathway while retrograde conduction was unimpaired and allowed the initiation of the observed reciprocating tachycardias. The diagnosis was based on the assumption that the ventricular myocardium was an essential link in the re-entry circuit. The three most important findings to support this assumption are: 1) retrograde conduction time, measured by the Q-A' interval (Q in ECG to atrial echo), and the rate of tachycardia were dependent on the mode of intraventricular conduction: 2) the first Q-A' interval of the tachycardia was independent of the A-H interval (initiation of atrial impulse to first activation of the His bundle) of the initiating premature atrial depolarization (PAD); 3) there was retrograde conduction following a ventricular premature beat during tachycardia at a time when the A-V node and/or the bundle of His would be refractory.