Evidence for Propagation of Activation Across an Accessory Atrioventricular Connection in Types A and B Pre-excitation

The sequence of atrioventricular activation was studied in two human subjects with type B Wolff-Parkinson-White syndrome (WPW) and in a dog with spontaneous type A WPW. In all three subjects a focal spot of pre-excitation was demonstrated at the A-V margin of the right ventricle (RV). In the two human subjects with type B WPW, the area of pre-excitation was located on the anterior aspect of the RV and in the dog with type A the pre-excited area was located on the posterior aspect of the RV. A probable Kent bundle electrogram was recorded from the A-V margin in one of the human patients. Serial sections (7 µ) of a block taken from the region of pre-excitation in the dog revealed an anomalous A-V communication (Kent bundle). Propagation velocity across this pathway was estimated to be 0.3 mm/msec. Electrophysiologic data recorded from one of the human subjects at the onset and during an episode of supraventricular tachycardia demonstrated an atrioventricular-atrial sequence of excitation. The mechanism of initiation of the tachycardia was a ventriculo-atrial echo following a premature atrial contraction blocked in the anomalous pathway. Surgical separation of right atrium and RV at the site of pre-excitation normalized the activation and ECG and abolished the tachycardia in both patients. Ventricular fibrillation occurred repeatedly in the dog as a direct result of the rapid ventricular rate permitted by the Kent bundle subsequent to induced atrial fibrillation. Correlation of the activation sequence with the body surface potentials suggests an updated conceptual model for electrocardiographic typing of WPW. In a third patient, who demonstrated an atypical form of WPW, the region of pre-excitation could not be precisely defined and interruption of an accessory pathway was unsuccessful.