Right superior septal artery with "normal" right coronary and ectopic "early" aortic origin: a contribution to the vascular supply of the interventricular septum of the human heart.

In the human heart, anterior and posterior septal branches are mainly responsible for the arterial supply of the interventricular septum. These arteries are the basis of efficient intercoronary collateralization. The right and left superior septal arteries also contribute to the nourishment of the septum and to any eventual collateralization. Because the right superior septal artery (RSSA) is small in diameter, short, and has a variable origin either at the proximal stem or in the ostial area of the right coronary artery, it is difficult or almost impossible to visualize it angiographically. During investigation of the arterial supply of the interventricular septum in 84 human heart specimens and 16 corrosion casts, we found a few peculiarities in the origin and pattern of the RSSA in four specimens. The RSSA was found in 27 cases (27%); in most it was a single vessel and arose from three different locations: (a) the proximal part of the right coronary artery (21 cases); (b) the right coronary ostial area (four cases); and (c) from the floor of the right (anterior) aortic sinus (two cases). Macroscopically, in 16 cases the RSSA had a length of less than 10 mm; in nine cases the arteries were between 11 and 17 mm long. In two cases the RSSA was of more substantial appearance and up to 36 mm in length; it nourished almost the entire upper third of the septal myocardium. In these two cases, two courses could be differentiated: an extramural course with the RSSA descending to the subvalvular fibrous tissue, and an intramural course with ramification in the myocardium of the crista supraventricularis and the superior parts of the interventricular septum. One cadaveric heart specimen and one corrosion cast showed RSSAs that originated "early" (ectopically) on the floor of the right (anterior) aortic sinus; their total lengths were 16 and 17 mm, respectively. Such ectopic ostia of RSSAs have never been described before in the anatomical literature. Given the intense clinical concern with the identification of possible bypass vessels in the myocardium, we assume that the RSSA may have a potential as a collateral route. These findings were also discussed in light of developmental and comparative anatomy.