INTRODUCTION His-Purkinje conduction delay, manifested by bundle branch block QRS complex configuration or by HV interval prolongation, is considered an essential condition for maintenance of bundle branch reentrant tachycardia (BBRT). METHODS AND RESULTS Of 178 patients with different types of ventricular tachycardia (VT), 13 were found to have BBRT as the underlying electrophysiologic mechanism. Of these 13 patients (9 men and 4 women; mean age 64 +/- 13 years), 6 had an HV interval < or = 55 msec (group A), and 7 had a prolonged HV interval (> 55 msec; group B) during sinus rhythm (SR). PR interval (169 +/- 32 vs 339 +/- 138 msec, P = 0.01) and QRS duration (116 +/- 17 vs 167 +/- 29 msec, P = 0.003) during SR were significantly shorter in group A than in group B. In group A, the HV interval was significantly longer during VT than during SR (73 +/- 18 vs 47 +/- 7 msec, P = 0.007). There were more patients with functional His-Purkinje block (split His potentials, a jump of HV interval induced by programmed atrial stimulation or burst pacing) or phase 3 block in group A than group B (6/6 patients vs 0/7 patients, P < 0.001). Successful ablation of the right bundle branch was performed in all 13 patients without deteriorating AV block. Two patients died in each group, and VTs (other than BBRT) or ventricular fibrillation were documented by ICD electrogram storages in 4 patients during follow-up of 27 +/- 17 months. CONCLUSION A prolonged HV interval during SR is not a prerequisite for BBRT. Functional His-Purkinje system abnormalities appear to be the electrophysiologic substrate for this specific type of BBRT.