The histopathological substratum for atrial fibrillation in man

Quantitative studies on the histological sections of the atria including sinoatrial (SA) node, SA junction and internodal preferential pathways in 12 hearts with long-term atrial fibrillation (Af group) and in 43 hearts with no arrhythmia (control group) have been carried out. The control group was subdivided into two age-groups, the younger and older over 50 years for the age-matched comparison with the Af group. In the Af group, markedly impaired contiguity of the SA junction, severe fibrosis and lipomatosis of atria were common precipitating factors. Regarding the ratio of SA nodal cells to the area of SA node, and patency of SA node artery, there were no significant difference between the Af group and age-matched (older) control group. In comparison between the two control groups, decreased SA nodal cells, stenosis of SA node artery, impaired contiguity of the SA junction, fibrosis and lipomatosis of atria were more prominent in the majority of the older group than that of the younger. These findings suggest that the pathological lesions of the SA junction and the atrial myocardium in the Af group were the exaggerated aging changes, and these lesions may be the main anatomic substratum for Af.