ABSTRACT
It is well established that left bundle branch block (LBBB) QRS morphology on the surface electrocardiogram (ECG) correlates with delayed activation of both endocardial and epicardial aspects of the left ventricle (LV) during normal sinus rhythm and during pacing from the apex of the right ventricle (RV).1-3 Likewise, it is true that most LBBB QRS pattern patients with heart failure have a left intraventricular uncoordinated contraction as a result of an LV free-wall mechanical delay. Thus, the electrophysiological and mechanical bases for CRT in a case of LBBB are widely accepted and support the use of biventricular pacing in order to correct this electrical and mechanical asynchrony. However, little is known about the electrophysiological and mechanical effects of right bundle branch block (RBBB) in heart failure patients.
