Single Coronary Artery from Right Aortic Sinus with Septal Course of Left Anterior Descending Artery and Left circumflex Artery

J INVASIVE CARDIOL 2007;19:E102-E103 The occurrence of a single coronary artery (SCA) in structurally normal heart is uncommon. This anomaly is often clinically benign and presents as an incidental finding during coronary angiography. Different types of SCA have been described and classified in the literature. We report a hitherto undescribed type of SCA originating from the right sinus of Valsalva in which the left anterior descending artery (LAD) has a septal course and the right coronary artery (RCA) continues as the left circumflex artery (LCX).

Case Report. A 73-year-old female with a history of hypertension and dyslipidemia presented with atypical chest pain of 6-months’ duration. Cardiac examination and baseline electrocardiography were normal. The echocardiogram revealed no wall motion abnormalities. During coronary angiography, attempts to cannulate the left coronary artery were unsuccessful. Cannulation of the RCA with a JR3.5 6-Fr catheter revealed a SCA originating from the right sinus of Valsalva at the usual position of the ostium of the RCA (Figures 1 and 2). Immediately after the origin, the artery bifurcated to the LAD and RCA. The LAD, after giving a septal artery, showed a septal course beneath the right ventricular infundibulum to surface at midseptum in the anterior interventricular (IV) groove. At this point, the LAD bifurcated into a larger superior branch and a smaller inferior branch. The upper division showed a retrograde course until the proximal IV groove where it terminated after giving two diagonals. No terminal branch of the LAD coursed into the proximal left atrioventricular (AV) groove. The lower smaller division of the LAD was reinforced with a major right ventricular branch arising from the proximal part of the RCA and coursing across the anterior right ventricular wall. The distal LAD supplied until the left ventricular apex. The RCA continued in the right AV groove to give the posterior descending artery at the crux. Thereafter, it continued as the LCX, which coursed along the entire length of the left AV groove, supplying the posterolateral aspect of the left ventricle. The aortic root angiogram showed no vessel arising from the left coronary sinus. No coronary artery stenosis was noted. The patient was kept on medical follow up.

Discussion. A single coronary artery is a rare coronary anomaly, particularly in the absence of structural heart disease. The incidence of an anomalous coronary origin ranges from 0.17% in autopsy studies¹ to 1.3% in angiography series.² The prevalence of SCA is reported to be less than 3% of all major coronary anomalies.² The frequency of SCA originating in the right or left aortic sinus is almost similar, though a right-sided origin shows a slightly higher preponderance.^3,4 In a study of 142 patients with a SCA, the common trunk arose from right aortic sinus in 49% of patients, and from the left aortic sinus in 45% of patients.³ Yamanaka et al reported a SCA arising from the right sinus of Valsalva in 0.019% of the patients in a large series of 126,595 patients undergoing coronary angiography.²
In single coronary arteries arising from the right aortic sinus, the left main coronary artery (LMCA) often arises from the proximal part of the common trunk and courses towards the anterior IV groove where it divides. Direct origin of the LAD from a right-sided SCA is quite uncommon.^2,4 In cases with direct origin of the LAD from the right aortic sinus or RCA, the circumflex originates from the left cusp, or rarely from right cusp with an anomalous retroaortic course to reach the left AV groove. Direct continuation of the circumflex from the terminal RCA in a SCA was reported only once previously.⁵ In that case, the LCX continued into the proximal anterior IV groove and the LAD had a retroaortic course before reaching the IV groove. The RCA continuing as the LCX has been termed as a “superdominant RCA” or “absent LCX” by a few authors.^5,6 However, as the term “superdominant RCA” has been used to describe a large RCA in the presence of a small LCX as well,⁷ we preferred to avoid these confusing terminologies.
Though an anomalous LAD arising from the right coronary system can follow any of the four courses (septal, anterior free wall, retroaortic, and interarterial) classically described for the LMCA, unlike the LMCA, it often follows either of the initial two courses. The differentiation of these two courses in two-dimensional coronary angiography can be made using Serota’s “dot and eye” method.⁴ In 30º RAO view, before turning to the apex at the midseptum, the LAD will pass left and downward (forming the lower half of the “eye”) in a septal course, while it will pass left and upward (forming the upper half of the “eye”) in an anterior free-wall or conal course. In a series of 21 adults with major anomalous origin of coronary arteries, 14 of them had a partial or entire left coronary artery arising from the right sinus or proximal RCA. Only 2 of these adults had an isolated LAD crossing towards the left side, with a septal and anterior free-wall course in 1 patient each.⁴
The septal course is the most common variant of the four courses of a LMCA arising from the right sinus and is largely benign.^4,8 No case of sudden cardiac death has yet been attributed to a septal course isolated from the LAD. Unless coronary arteries have an interarterial course, a SCA is considered a benign condition, as in our patient in whom this anomaly was incidentally detected at the age of 73 years.
Another rarity in the angiogram was that the LAD beyond the midseptum was reinforced with a right ventricular branch. Such reinforcement in association with a SCA has not been described previously.
The coronary anatomy in this patient does not fall into any category of SCA in the classification by Lipton et al⁹ as a septal course of the LMCA or LAD had not been considered by them when the classification was formulated. Lipton used only three final designations as “A”, “B”, and “P”, referring to “anterior”, “between”, and “posterior” patterns to describe the course of an anomalous artery. To our knowledge, the combination of a circumflex continuation of the RCA and a septal course of the LAD in a SCA arising from the right aortic sinus has not been previously reported.