An aged case of trifascicular block with special reference to a histological study of the conduction system.

A histological study by serial sections of the conduction system was performed in a case of 84-year-old female with a diagnosis of hypertension and complete atrioventricular (AV) block. The course of her electrocardiogram was divided into 6 stages as follows: 1) left ventricular hypertrophy (11 years before), 2) complete right bundle branch block (CRBBB) and no axis deviation with PQ interval of 0.20sec (10 years before), 3) C-RBBB with right axis deviation (2 years before), 4) advanced AV block with occasional ventricular capture, 5) C-RBBB with left axis deviation for 10 days' duration (1 year and 3 months before), and 6) complete AV block with the idioventricular rhythm with RBBB type (terminal 1 year). There were moderate fibrosis in the AV node with partial destruction of conduction cells and the same fibrotic changes in the proximal portion of the AV bundle. The proximal portions of posterior and anterior fascicles of the left bundle branch were completely interrupted by the marked endocardial fibrosis. The right bundle branch showed sporadic fibrosis in the first portion, but in the second portion the conducting cells were thoroughly destroyed. The above-mentioned findings were compatible with the trifascicular block reported by Rosenbaum in 1969, in both the electrocardiographic and histological findings.