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

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