Considerations on the sinus node microangioarchitecture.

The importance of the sinus node as the cardiac pacemaker is well known. The aim of the present study was to investigate the microangioarchitecture at the level of the sinus node. Ten human adult hearts were injected with India ink in the initial segments of the coronary arteries. Pieces were drawn and diaphanized. The results of the study can be summarized: (1) the sinus node is rather an irregularly shaped structure, with peripheral strands intermingling with strands of the atrial myocardium; at this level two vascular patterns can be recognized: (a) the myocardial capillary networks that parallels the muscular bundles, and (b) the peripheral nodal networks built upon dichotomizing arterioles; (2) it seems that while the thick and large sinus node artery does not branch in the nodal tissue, the blood supply of this tissue is ensured by the peripheral nodal networks; (3) characteristically, in the periphery of the nodal tissue are largely present glomeruli made by capillaries with pericellular dispositions. The results strongly suggest that the nodal tissue is mainly supplied from its periphery and the sinus node artery is rather a scaffold than a supplier of that tissue.