An Unusual Coronary Trinity: Single Left Coronary Artery with the Right Coronary Artery Originating from the Left Main Coronary Artery and Following a Retro-Aortic Course

ABSTRACT: All three coronary arteries originating from a single coronary ostium is a rarity. Single coronary artery (CA) arising from the left aortic sinus is far more uncommon than one arising from the right sinus. Usually in such cases, the right coronary artery (RCA) arises as a distal continuation of the left circumflex artery. We describe an extremely uncommon anatomic variant, where the RCA arose from the single undivided CA as a branch of the left main coronary artery and followed a retro-aortic course before reaching its designated anatomic territory.

J INVASIVE CARDIOL 2011;23:E156–E157

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Congenital anomalies of coronary arteries are infrequent and usually incidentally detected during routine coronary angiography performed to evaluate coronary artery disease. A single coronary artery (CA) occurring in isolation, without associated congenital heart disease, is one of the rarest coronary anomalies. We describe an extremely uncommon variant of a single CA, where the right coronary artery (RCA) originated as a branch of the left main coronary artery (LMCA), and followed a retro-aortic course, before coursing in its normal territory.

Case Report. The patient was RS, who underwent coronary angiography for evaluation of exertional angina. Cannulation of the left aortic sinus using a JL 4 catheter revealed a single coronary artery that divided into left anterior descending (LAD) and left circumflex (CX) arteries, with the posterior descending (PDA) arising from the distal CX artery. The RCA also arose from the undivided common trunk of the LMCA, and coursed retro-aortic to the aorta, reaching the right atrioventricular (AV) groove. The RCA gave off the marginal branches to the right ventricle as well as a few posterior left ventricular (PLV) branches (Figures 1–3). Only mild atherosclerotic changes were noted in the coronary arteries, without any significant flow-limiting lesions. The patient was stabilized on medical therapy and is presently well at 1-year follow-up.

Discussion. By definition, a single coronary artery arises from the aortic trunk by a single coronary ostium and supplies the entire heart. A single CA occurring in isolation, without associated congenital heart disease, is a rare anomaly with a reported incidence of 0.02–0.04% of the general population.¹ The classification of single CA proposed by Shirani et al² categorizes patterns primarily on the basis of the location of the solitary coronary ostium (whether from the left or right aortic sinus, respectively) and the course taken by the aberrantly coursing coronary artery. The classification proposed by Lipton, on the other hand, categorizes patterns according to whether the aberrantly coursing artery (RCA or LCA) originates from the single undivided CA or as a branch of the individual coronary arteries.³

Type I pattern: The single CA may arise from the right or left aortic sinus. When the single CA arises from the left sinus, after giving off the LAD and left CX, it continues beyond the crux into the right AV groove, with the RCA arising as branches from the mid/distal CX. When the single CA originates from the right sinus, it courses like a normal RCA and after giving off the PDA, it continues in the left AV groove, giving off the PLV branches. Finally, it gives off the LAD as its terminal branch. 

Type II pattern: The single CA arises from the right or left aortic sinus and the contralateral (be it the LCA or RCA, respectively) arises proximally from the single undivided CA and crosses the base of the heart to course in its respective territory.

Anomalously arising RCA as a branch of single CA, though very rare, has been reported in the past. However, almost all such cases are Type I pattern, where the anomalous RCA arises either as a branch of the LAD^3–7 or from the mid or distal portion of the left CX in the AV groove.^8–10

In contrast, the Type II pattern of anomalously arising RCA, where it arises proximally from the single undivided CA or LMCA (as occurred in our case), is an extremely uncommon variant.¹¹ Such an anomalously arising RCA may follow any of the three anatomic courses: A (anterior to right ventricular outflow tract); B (between the aorta and pulmonary artery); or P (posterior to aorta).^2,3 Of these, the A and B patterns are the most frequent, while pattern P, with retro-aortic course, is reported to be the rarest. Our case conformed to Type II P, since the anomalously arising RCA followed a retro-aortic route, before coursing in its normal territory. 

By itself, a single CA (in absence of other congenital heart disease) usually does not cause symptoms and is generally detected incidentally during coronary angiography. Though most cases are asymptomatic, angina-like symptoms can occur due to acute takeoff angles, slit-like orifices, luminal compression by anomalous course between aorta and pulmonary artery, or even accelerated atherosclerosis.^12–14 Our case had only mild atherosclerotic changes and was stabilized on medical therapy. The patient is asymptomatic at a follow-up of 1 year.

Conclusion. It is important to think of and recognize anomalously arising coronary arteries whenever one encounters difficulty while performing a coronary angiogram. Single coronary artery from the left aortic sinus with RCA arising as a branch of the undivided LMCA is an extremely uncommon anomaly. Cardiologists need to be aware of the various aberrant anatomic locations and courses of such arteries to be able to adequately define coronary anatomy in each case.

References

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From ¹the Departments of Cardiology, Sanjay Gandhi Post-Graduate Institute of Medical Sciences, Lucknow and ²Jaswant Rai Specialty Hospital, Meerut, India.
The authors report no conflicts of interest regarding the content herein.
Manuscript submitted September 13, 2010, final version accepted October 4, 2010.
Address for correspondence: Dr. Aditya Kapoor, Additional Professor, Cardiology, Sanjay Gandhi PGIMS, Rae Bareli Road, Lucknow 226014. Email: akapoor65@gmail.com