Histopathological Study on the Conduction System of Complete Right Bundle Branch Block

Eleven autopsy cases (average age of 71 years) with complete right bundle branch block were examined histologically with serial sectioning of the conduction system. The results were as follows: 1) moderate to severe reduction of conducting cells in the right bundle branch (RBB) by fibrous replacement in all 11 cases, 2) a preponderance of main lesions in the first portion of the RBB in cases with R configuration in leads V1 and V2, and in the second to the third portion without significant lesion of the Purkinje cell network in the right ventricle in cases with rsR', rSR', and RSR' configuration in these leads, 3) as to the etiology, 1 case was assumed to have had rheumatic myocarditis and an another case, 1 chronic ischemia. In cases in which the cause could not be clearly established, reduction of the conducting cells in the first portion of the RBB was thought to be due to fibrosis of the upper ventricular septum. Lesions in the second portion of the RBB may be due to mechanical strain effected by muscle crossing of the trabecula septomarginalis and RBB.