Hype and hope in the use of echocardiography for selection for cardiac resynchronization therapy: the Tower of Babel revisited.

Initially, the rationale behind the use of echocardiography to assess mechanical synchrony seemed straightforward. Not all patients with left bundle-branch block (LBBB) have mechanical dyssynchrony, and this entity could be identified by measuring the contraction delay between different cardiac walls. It was hoped that better selection with echocardiography would minimize the nonresponder rate of cardiac resynchronization therapy (CRT).