Catheter ablation of an antidromic atrioventricular reentrant tachycardia using a slow, decrementally conducting accessory pathway in the great cardiac vein.

The inability to ablate left accessory pathways (APs) from endocardial approaches may suggest an epicardial location. We report on a 43-year-old woman presenting with a wide QRS tachycardia with Right Bundle Branch Block (RBBB) morphology, right inferior axis, and the "pattern break" appearance in V2 resembled the outflow tract ventricular tachycardia. An electrophysiology study confirmed an antidromic atrioventricular reentrant tachycardia using an antegrade slow, decrementally conducting AP that was successfully ablated in the great cardiac vein-anterior interventricular vein junction after failure of endocardial approach.