Electrophysiological studies demonstrate that tachycardias in WPW type A are easily initiated and terminated by left-sided stimuli, supporting a left-sided anomalous pathway and a reentrant mechanism.
The initiation and termination of tachycardias were studied in five patients with Wolff-Parkinson-White syndrome, type A. In all patients, electrical stimulation was performed from the right side of the heart. In three patients the effect of induced left-sided premature beats was studied as well. In contrast to patients with Wolff-Parkinson-White syndrome, type B, there was difficulty in initiation and termination of tachycardias with premature beats applied to the right atrium or ventricle. This could easily be accomplished with left-sided premature stimuli. In two patients the simultaneous recording of right and left atrial activation during a tachycardia, showing atrioventricular conduction by way of the A-V nodal-His pathway and ventriculoatrial conduction via the anomalous connection, revealed that left atrial activation occurred far in advance of right atrial activation. During regular driving of the right and the left atrium at identical rates the most pronounced pre-excitation pattern was seen after left atrial stimulation. Our results are in agreement with a circus movement or reciprocal mechanism by way of the A-V nodal-His pathway and the anomalous A-V connection as a causal mechanism for tachycardias in Wolff-Parkinson-White syndrome, type A. In contrast to the usual finding of atrioventricular conduction during the tachycardia via the A-V nodal—His pathway and ventriculoatrial conduction by way of the anomalous connection, one patient showed tachyeardias running in the opposite direction. A location of the anomalous pathway on the left side of the heart is supported by our findings.
Wellens et al. (Fri,) studied this question.