Intra-atrial course of the right coronary artery and its branches.

OBJECTIVE: To illustrate and describe an anomaly of right coronary artery (RCA) course.

SETTING: Postmortem examination of cardiac tissue.

DESIGN AND PATIENTS: Three cases where the RCA had an intracavitary position in the right atrium are described. Additionally, light microscopic analysis of random sections of posterior right atrium from 100 consecutive autopsy cases was undertaken.

MAIN RESULTS: Each of the index cases was an incidental finding at autopsy. In two cases, the RCA, after passing the acute angle of the heart (epicardially), entered the right atrium posteriorly and ran subendocardially for distances of 1.5 and 3.0 cm, respectively. In the third case, the RCA entered the right atrial cavity 2.5 cm from its origin and ran subendocardially for 2.0 cm. In all three cases, the RCA exited the atrial cavity and once again attained an epicardial course. In the first two cases, the RCA ran 1.0 cm above the atrioventricular groove, rather than in its normal location at the annulus. The random sections of right atrial wall showed that medium calibre arterial branches of the RCA also commonly run in subendocardial positions (29 of 100 cases) and sometimes project into the atrial cavity (five of 29 cases).

CONCLUSIONS: The genesis of this epicardial coronary anomaly is unclear, but may relate to the 'higher' than normal course of the artery in these cases, in concert with the normal thinness of the right atrial wall, and the tendency for even medium calibre arteries to assume this subendocardial location. Despite the benign outcome of the index cases described here, the authors believe that this intracavitary course of the RCA could pose special technical problems during coronary artery catheterization and bypass grafting.