Arterial blood supply of the atrioventricular node and main bundle.

The arterial blood supply of the A V node and main bundle has been studied in I0 normal hearts. In each heart i5o to 200 histological sections of the A V node region wore analysed and thefindings correlated with magnified postmortem angiograms. This enabled determination of the origin of the supplying artery, the ramus septifibrosi, and its ramifications within the node. In all hearts the ramus septifibrosi originatedfrom the right coronary artery. Its course appears to be less constant and anatomically less closely related to the specific conducting tissue than that of the sinus node artery. In most hearts the artery entered the dorsal margin of the node, made a sharp caudal turn (5o to go degrees) approximately in the middle of the node, and penetrated again into the adjacent myocardium. Usually only a small branch continued the original course in the longitudinal axis towards the main bundle. The relatively poor blood supply of the main bundle was Jfurther shown by planimetric measurements of the arterial and arteriolar lumina. The arterial density was approximately I0 times greater in the dorsal part of the node than in the main #bundle. Collateral blood supply was studied by injection of the left coronary artery. No direct anastomoses between the penetrating septal branches of the left anterior descending artery and the ramus septifibrosi could be outlined. It is concluded that, from the viewpoint of blood supply, the main bundle and the ventral third of the A V node are more vulnerable than the dorsal part. This finding is correlated with some clinical studies in patients with AV block complicating acute myocardial infarction.