Case report: Wide-complex tachycardia one week post-CRT-D implantation in a patient with pre-existing left bundle branch block.

A 37-year-old female with dilated cardiomyopathy, whose baseline ECG showed sinus rhythm with left bundle branch block pattern, received a cardiac resynchronization therapy defibrillator (CRTD). One week post-implantation, she presented to the emergency department with palpitations, diaphoresis and chest discomfort. ECG showed a wide-complex tachycardia (WCT) episode, which spontaneously converted to sinus rhythm, and was later diagnosed as typical slow-fast atrioventricular nodal re-entrant tachycardia. This report outlines the differential diagnoses for WCT and the reasoning behind the eventual diagnosis, taking into consideration the device interrogation findings and results of the electrophysiology study.