A clinicopathological study on the sick sinus syndrome.

A total of 6 cases of sick sinus syndrome were presented, including 2 cases of sinoatrial (SA) block and 4 cases of bradycardia-tachycardia syndrome. There were 2 men and 4 women, and their ages ranged from 69 to 91 years. Electrophysiological studies were performed in 3 cases, showing positive overdrive suppression in 1 and normal atrioventricular (AV) conduction in 3. Syncopal attacks were found in 4 cases, and 2 cases died suddenly. Histological examination of the SA node and AV conduction system disclosed (1) marked reduction of the SA nodal muscle fibers by 70 t0 80%, (2) moderate to marked proliferation of connective tissues in the SA node, and (3) moderate fibrosis in part of the left bundle branch. The SA node artery was patent.