Mechanisms determining the ventricular rate in Wolff Parkinson White arrhythmias

In patients with WPW syndrome the maximal ventricular rate attained during ectopic rapid supraventricular rhythms depended on the type of arrhythmia as well as on the physiological properties of the accessory pathways (AP). During reciprocating tachycardias the impulse is almost invariably conducted to the ventricles through the AV node. Therefore the maximal ventricular rate is a function of the atrio ventricular (AV) nodal effective refractory period (ERP). On the other hand, when atrial flutter or atrial fibrillation was present the ventricular rate could be moderately elevated (when the ERP of the AP was longer than that of the AV node) or very rapid where the ERP of the AP was significantly short. Therefore, from the electrophysiological viewpoint, the AP appears to behave as His Purkinje tissue in some cases and as ordinary atrial muscle in other patients. These assumptions await further documentation.