Left ventricular mechanical dyssynchrony by cardiac magnetic resonance is greater in patients with strict vs. conventional ECG criteria for left bundle branch block

Background Left bundle branch block (LBBB) is a marker of increased delay between septal and left ventricular (LV) lateral wall electrical activation, and is a predictor of which patients will benefit from cardiac resynchronization therapy (CRT). Recent analysis has suggested that one third of patients meeting conventional ECG criteria for LBBB are misdiagnosed and new strict LBBB criteria have been proposed. We tested the hypothesis that strict LBBB patients have greater LV mechanical dyssynchrony than patients only meeting conventional LBBB criteria, while there is no difference between patients with conventional-only LBBB and LV conduction delay with QRS duration 110-119 ms.