Electrocardiographic and electrophysiological characteristics of ventricular arrhythmias from the right bundle branch of the moderator band

Background: There are little data on ventricular arrhythmias (VAs) originating from the right bundle branch (RBB) of the moderator band (MB) (MB-RBB VAs) in a cohort of patients.

Objective: The purpose of this study was to investigate the electrocardiographic and electrophysiological characteristics of MB-RBB VAs.

Methods: Sixteen patients with MB-RBB VAs and 5 patients with right ventricular (RV) anterior papillary muscle (APM) VAs (RV-APM VAs) were studied under the guidance of intracardiac echocardiography.

Results: The MB-RBB VAs group demonstrated a typical left bundle branch block pattern with left superior axis deviation and a narrower QRS complex during VAs (P < .001) as compared with the RV-APM VAs group. Furthermore, the MB-RBB VAs group had a shorter rS interval, a sharper slope of the S wave downstroke without notching in leads V₁ and V₂, and a shorter r wave duration in lead V₂. A leading RBB potential at the target during VAs was observed for all patients in the MB-RBB VAs group, which was also present during sinus rhythm for all patients, except for 2 with RBB block at baseline. Ablation of the leading RBB potential effectively eliminated the arrhythmia. In the RV-APM VAs group, no Purkinje potential at the target was identified in any patient during VAs.

Conclusion: QRS morphology of MB-RBB VAs is characterized by a typical left bundle branch block pattern with a relatively narrow QRS complex, short r wave and rS durations, and a sharp S wave downstroke without notching in leads V₁ and V₂. Mapping and ablation of the leading RBB potential are effective in eliminating VAs.