Bradycardia-Dependent Bundle-Branch Block

Abstract

Four cases of bundle-branch block (BBB) occurring with slow heart rates in patients with heart disease are presented. Recognition of bradycardia-dependent BBB is often difficult, and its differentiation from ventricular escape mechanism and from bilateral BBB requires careful analysis. A set of five criteria based on our own observations is presented with a review of the literature. The responsible mechanism for this seemingly paradoxical situation is not known. However, spontaneous depolarization of one or the other of the bundle branches in late stages of diastole appears to be the most plausible explanation.