Arrhythmias from the Right Ventricular Moderator Band: Diagnosis and Management

The moderator band in the right ventricle is being increasingly recognised as a source for arrhythmias in the absence of identifiable structural heart disease. Because it carries part of the conduction system from the right ventricle septum to the free wall, it is a source of Purkinje-mediated ventricular arrhythmias that manifest as premature ventricular contractions (PVC) or repetitive ventricular tachycardia. More importantly, short coupled PVCs triggering polymorphic ventricular tachycardia and VF have been localised to the moderator band and ablation of these Purkinje mediated PVCs can effectively prevent recurrent VF. The exact mechanism of arrhythmogenesis is still debated but stretch, fibrosis and ion channel alterations might be responsible. Arrhythmias originating in this region of the right ventricle may thus be another cause for idiopathic VF that is potentially treatable with catheter-based ablation techniques. Recognition of the typical PVC morphology can point to the moderator band as the source of idiopathic VF and an opportunity for timely intervention. The available data on the anatomy, electrophysiology and management options are reviewed.