Repetitive polymorphic ventricular tachycardia initiated by phase 4 block in the His-Purkinje system.

We report a case of a patient who developed repetitive episodes of polymorphic ventricular tachycardia with a stereotypical pattern of initiation. A premature atrial complex would result in a brief pause followed by left bundle branch block aberrancy. Ventricular bigeminy would ensue followed by episodes of polymorphic ventricular tachycardia, some requiring cardioversion. We postulate that delay within the His-Purkinje system initiated by phase 4 block was proarrhythmic in this patient.