The occurrence of phase-4 block in the anomalous bundle of patients with Wolff-Parkinson-White syndrome.

Conduction in the Kent bundle was studied in 17 patients with WPW syndrome, before and after administration of ajmaline and amiodarone. Before drug administration, only one patient showed phase-3 block and only one other showed phase-4 block. After administration of ajmaline to 11 patients and amiodarone to 16 patients (each patient received at least one of the drugs and the two drugs were given independently to 10 patients), the occurrence of phase-3 block alone in the Kent bundle was documented in 9 patients of the 17, phase-4 block alone in 1, and phase-3 and phase-4 block together with a typical accodion in 3. In 4 patients conduction in the Kent bundle was not modified. The phase-3 and phase-4 block as well as the accordion effect in the Kent bundle were similar to the same phenomena previously described in patients with diseased or in dogs with injured intraventricular conducting fascicles. The fact that the Kent bundle can show the same physiological and pharmacological behavior as a diseased His bundle or bundle branches is highly significant, first, because it may indicate that the anomalous bundle is also composed of Purkinje or Purkinje-like fibers and, secondly, because it may help to distinguish a normal from a diseased Kent bundle, and this may become essential for determining the prognosis and treatment of patients with WPW syndrome. The Kent bundle can be compared with a normal or diseased extra-His bundle.