Successful Epicardial Ablation of a Right Infero-paraseptal Accessory Pathway Presenting as Ventricular Fibrillation.

A 22-year-old man presented with aborted sudden cardiac arrest due to ventricular fibrillation and recurrent tachyarrhythmia related to a right inferoparaseptal accessory pathway. A previous electrophysiology study with both endocardial and epicardial ablation had failed. Repeat electrophysiology study demonstrated diffuse early activation on endocardial mapping but a focal earliest site during epicardial mapping. The successful ablation site showed a sharp QS in the unipolar electrogram with a contact force vector directed toward the visceral pericardium/myocardium and required careful catheter positioning away from the distal right coronary artery. Accessory pathway conduction was abolished within 4.9 seconds of radiofrequency delivery. This case highlights the importance of properly analyzing the electroanatomic map, detailed electrogram analysis, and procedural safety considerations during epicardial accessory pathway ablation.