Localized Conduction Delay in the Proximal Bundle Branch Region in Bundle Branch Reentrant Ventricular Tachycardia Without Structural Heart Disease

INTRODUCTION: We report a rare case of successful ablation of type A and type C bundle branch reentrant ventricular tachycardia (BBR-VT), in which the conduction disturbance was localized just below the His bundle. METHODS AND RESULTS: Both type A and type C BBR-VTs were induced by constant ventricular pacing and could be entrained from the mid-right ventricular (RV) septum. Although the HV interval was prolonged during both tachycardias compared with sinus rhythm, the left bundle-left ventricular and right bundle-RV intervals remained unchanged. These findings indicated that the conduction disturbance responsible for both tachycardias was located at the proximal portion of the bundle branches. Ablation targeting the right bundle successfully terminated the tachycardia, after which no recurrence was observed during 9 months of follow-up. CONCLUSION: The conduction disturbance underlying HV interval prolongation during BBR-VT can be localized to the infra-His region, specifically at the proximal portion of the bundle branches.