Proarrhythmic Effect of RF ablation on the Right Ventricular Moderator Band

The right ventricular moderator band (MB) is increasingly being recognized as a source for PVCs and PVC-mediated ventricular fibrillation. Monomorphic PVCs, non-sustained monomorphic VT and ventricular fibrillation are all documented arrhythmias originating from the MB. The benign PVCs usually have a coupling interval in excess of 400 msec. When PVCs trigger VF, coupling intervals are typically short, less than 300 msec. We report here a case of long-standing frequent monomorphic PVCs with a coupling interval of > 400 msec from the right ventricular distal conduction system embedded in the moderator band that progressed to non-sustained ventricular tachycardia. Following suppression of the arrhythmia with RF ablation, the arrhythmia recurred with PVCs at a shorter coupling interval (<300 msec), with frequent repetitive non-sustained polymorphic VT and triggering of sustained ventricular fibrillation. The use of a cryoballoon to ablate over the course of the moderator band resulted in complete and durable suppression of ventricular arrhythmias.