An unusual form of bundle branch reentrant tachycardia

Introduction: We report the case of a 36-year-old patient with a longstanding history of paroxysmal tachycardia. Methods and Results: During the electrophysiological study, the H-V interval was prolonged in sinus rhythm, and a second potential (H') with distal to proximal activation pattern was recorded in the region of the proximal His-Purkinje system. Two wide QRS complex tachycardias were induced, both with V-A dissociation. One application of radiofrequency energy at the site with earliest and largest H' potential during sinus rhythm cured both tachycardias. The right and left bundle branch block morphology tachycardias were diagnosed as clockwise and counterclockwise bundle branch reentrant tachycardia. The H' potential represented the retrograde right bundle potential during sinus rhythm and bundle branch block reentrant tachycardia.