Pathological studies in sinoatrial disorder (sick sinus syndrome).

Necropsy data from a series of 8 patients diagnosed during life as having chronic sinoatrial disorder (sick sinus syndrome) are presented. The morphology of the cardiac conducting system was studied by serial section, and the coronary vasculature was examined in detail in 5 of the 8 patients by the injection of a radiopaque medium, and in all 8 by routine histological methods. The sinoatrial nodes were found to be abnormal in 7 of the 8 patients. In 4 the node was atrophic, in 3 there was a pronounced increase in the amount offibrous tissue present in the node, and in only one case did the node appear normal on light microscopy. In 1 of the 3 patients withfibrosed nodes amyloid tissue wasfound in the node itself, and heavy deposition was noted in the atrial musculature surrounding the node. The sinoatrial-node artery was patent in all cases and major narrowing of the larger coronary arteries was found in only 1 case. Histological abnormalities were found in the atrioventricular conducting tissue in all but 1 case, changes being seen either in the atrioventricular node or in the His-Purkinje system. It is concluded that the aetiology of sinoatrial disease is multifactorial, but that at least in the cases studied coronary arteriosclerosis was not responsible.