Rate dependent left bundle branch block with gradual transition between normal intraventricular conduction and complete left bundle branch block. A case report.

A case of 70-year-old woman with ischemic heart disease is presented. The electrocardiogram showed atrial fibrillation and a tachycardia-dependent, left bundle branch block. A number of intermediate QRS patterns from normal intraventricular conduction to complete left bundle branch block were seen, and the transition was gradual. Increasing grades of aberrance were seen following a shorter preceding cycle length.