Right posterolateral sinoatrial nodal artery: Rare in the West but absent in the East?

In 60% to 70% of the population, the sinoatrial nodal artery (SANA) follows the idiomatic “path of least resistance” via embryonic coronary plexus pruning. It arises from the proximal right coronary artery, courses within the subepicardial fat, crosses anterior to the superior vena cava, passes beneath the right atrial appendage, and reaches the sinoatrial node at the superior-lateral junction between the superior vena cava and the right atrium, over a distance of approximately 6 cm. However, in 10% to 15% of cases, the SANA originates from the mid circumflex artery within the atrioventricular groove. It then assumes an S-shaped course, running along the roof of the left atrium beneath the left atrial appendage and looping over the left superior pulmonary vein. This trajectory renders the SANA particularly vulnerable to injury during radiofrequency atrial flutter catheter ablation and in related cardiac surgery. An 89-year-old man underwent coronary angiography following a myocardial infarction. In addition to an occluded left anterior descending artery, he was found to have a SANA that arose from the posterolateral branch of the right coronary artery and, like the S-shaped SANA, coursed along the atrioventricular groove. In contrast, this vessel took a circular route that was at least 3 times longer than the direct route. In this case, because the SANA originated adjacent to the atrioventricular nodal artery, an infarction in this territory could potentially cause extensive conduction system failure. However, this anatomical variation is rare, with a reported prevalence of under 1% in the west, and is practically unreported in the east.