Arrival of excitation at right ventricular apical endocardium in Wolff-Parkinson-White syndrome type A, with and without right bundle-branch block.

Filtered bipolar right ventricular apical (RVA) and His bundle electrograms, using electrodes only i mm apart, were recorded in two patients with intermittent WPW type A with and without 'complete' right bundle-branch block. In beats with exclusive normal pathway conduction and 'complete' right bundle-branch block, the HV and V-RVA intervals represented His-to-left ventricular endocardial and left ventricular endocardial-RVA conduction times, respectively. The H-RVA interval was determined by addition of these two intervals. In 'fusion' beats resulting from AV conduction through both normal and accessory pathways, the duration of the H-RVA interval was similar to that of beats with exclusive normal pathway conduction, suggesting that though the ventricles were pre-excited through an accessory pathway the RVA was still activated via the impulse emerging from the right bundle-branch. In beats with exclusive, or predominant, accessory pathway conduction and a WPW type A morphology, the H-RVA 'interval' was 'shorter-thannormal', suggesting that the RVA was not activated by the impulse traversing the normal pathway but by the one propagating from the pre-excited site. The corresponding V-RVA intervals (giving a rough estimate of conduction time from pre-excited site to RVA) were longer (Iio and I20 msec, respectively) than in two other patients with WPW type B. Intracardiac recordings have enhanced our knowledge of the ventricular activation process in WPW type A, either pure or associated with 'complete' right bundle-branch block.