Abstract Body (Do not enter title and authors here):
Introduction:
Premature Ventricular Contractions (PVCs) are often a benign arrhythmia. However, those originating from the Purkinje system can result in fatal arrhythmias. One example is PVCs originating from the moderator band (MB) within the right ventricle (RV) of the heart. We present a case of PVCs originating from the MB triggering idiopathic ventricular fibrillation (VF) and electrical storm.

Case:
A previously healthy 49-year-old woman was admitted following a witnessed VF cardiac arrest. She had recurrent episodes of VF, initially treated with Amiodarone and Procainamide which failed to suppress the recurrent VF. She received 54 external defibrillations before a transvenous pacer (TVP) was placed to override the PVCs at a pacing rate of 110 bpm. Post-resuscitation ECGs revealed frequent PVCs originating from the RV free wall, potentially from the lateral part of MB (Figure 1). Quinidine was added to suppress the PVCs ultimately allowing removal of the TVP. Transthoracic Echocardiogram revealed normal cardiac function and a prominent MB. A cardiac MRI was performed showing no infiltrative disease or any other abnormalities. The patient underwent sympathectomy and defibrillator placement. Despite recurrent cardiac arrest, she had excellent neurologic recovery and was subsequently discharged on Quinidine.

Discussion:
MB extends from the septal wall to the base of the anterior papillary muscle in the RV, carrying Purkinje fibers(PF) from the right bundle branch as it exits the septum. Purkinje fibers have been shown to initiate arrhythmias by several mechanisms including enhanced automaticity, triggered activity and re-entry. In the genesis of PVCs, triggered activity is the likely mechanism. This can degenerate into VF in a structurally normal heart, hence the term “idiopathic VF”. Familiarity with this entity and ECG features of MB ectopy leads to timely management and may potentially prevent lethal arrhythmias in symptomatic patients with such PVCs. Further studies are required to fully understand the arrhythmogenic mechanisms and the optimal management approach for MB ectopy.