Of special interest in the identification of those at a high risk of sudden death in this situation are subjects with intraventricular conduction defects - right and left bundle branch block. One reason for this is the possibility that such electrocardiographic findings may serve as markers for clinically unrecognizable ischemic heart disease. Of greater importance is the fact that right bundle branch block in conjunction with either marked right or marked left deviation of the mean frontal plane QRS vector has been considered to represent bilateral bundle branch block. Progression to involve the rest of the conduction system would produce complete heart block, which could result in sudden death. Similarly, left bundle branch block could lead to sudden death if involvement of the right bundle branch occurs, but it can also play a role in the genesis of potentially fatal cardiac arrhythmias.

The purpose of this study was to examine the relationship between sudden death and the presence of these intraventricular conduction defects, right and left bundle branch block, in men without clinical evidence of cardiac disease.