Angiographic Enigma: A Single Coronary Artery with the Right Coronary Artery Originating from the Distal Left Circumflex Artery

Abstract

An isolated single coronary artery (SCA) is a rare anomaly. A SCA originating from the left sinus of Valsalva is even rarer than one arising from the right. Most patients with a congenital coronary artery anomaly are asymptomatic. Herein, we report an extremely uncommon variant, where the right coronary artery arose from the distal segment of the left circumflex artery with slow coronary flow leading to myocardial ischemia.

INTRODUCTION

Congenital coronary artery anomalies regarded as an uneven diverse group of congenital disorders with variable clinical manifestations and pathophysiological mechanisms, are infrequent and usually detected incidentally during routine coronary angiography performed for the evaluation of coronary artery disease (CAD).[1] A single coronary artery (SCA) occurring in isolation, without associated structural heart disease, is very rarely reported in medical literature. We present a patient where the right coronary artery (RCA) originated as a branch of the distal left circumflex (LCX) artery.

CASE REPORT

A 60-year-old diabetic, hypertensive, nonsmoker male complaining of atypical chest discomfort with no family history of CAD was admitted in our hospital. Cardiac auscultation and peripheral pulses were normal. Baseline electrocardiogram was normal. An echocardiogram revealed normal atrioventricular morphology with normal biventricular functions and no regional wall motion abnormality. Serial cardiac enzymes were normal. Treadmill test was positive for inducible myocardial ischemia [Figure 1a and b]. The patient underwent a coronary angiogram for the evaluation of CAD in view of the positive stress test and risk factors. Cannulation of the left coronary ostium using a 5F radial optitorque catheter (Terumo R Inc., Tokyo, Japan) revealed a SCA that divided into the left anterior descending (LAD) and the LCX arteries. The LCX artery was the dominant vessel; it coursed beyond the atrio-ventricular groove up to the level normally occupied by the RCA [Figure 2a and b]. Since we were not able to cannulate the right coronary ostium, aortic root angiography was performed to exclude an abnormal take-off of the RCA [Figure 3]. Only a single left coronary ostium was seen to arise from the aorta. Review of all the angiographic images confirmed an isolated SCA with the RCA originating from the distal LCX. Since our patient had occasional chest discomfort with moderately positive stress test and no evidence of significant atherosclerotic CAD, he was managed with medical therapy.

Figure 1.

(a) Baseline 12 lead electrocardiogram showing normal sinus rhythm with no ST-T abnormality. (b) Electrocardiogram recording during stage II of treadmill tests revealing 2 mm ST depression in V3–V6 leads

Figure 2.

(a) Coronary angiogram left anterior oblique caudal view showing the dominant left circumflex (LCX) with right coronary artery originating from the distal segment of LCX. (b) Right anterior oblique caudal view: Single coronary artery bifurcating into left anterior descending and left circumflex (LCX) with right anterior oblique arising from the distal LCX and coursing beyond the atrio-ventricular groove

Figure 3.

Aortic root angio revealing left main coronary artery arising from left sinus of Valsalva and absent right coronary ostium

DISCUSSION

Congenital coronary artery anomalies are infrequent, with variable severities, ranging from mild to profound anatomical abnormalities and clinically diverse presentations. Most anomalies are incidentally detected during routine coronary angiographic evaluation of CAD, with a 0.64–1.3% incidence rate.[2,3] Isolated SCA is extremely rare, with an incidence rate of 0.024–0.066% in the general population.[4] However, an SCA is found more frequently in association with congenital heart disease, particularly persistent truncus arteriosus and pulmonary with the incidence rate of 18.5% and 17%, respectively.[5,6]

The classification of SCA proposed by Lipton et al. categorizes patterns according to the site of origin and anatomical distribution.[7] The anomalous coronary artery is first designated with “R” or “L” depending upon whether the ostium is located in the right or left sinus of Valsalva. It is then designated as Group I, II or III.

• Group I pattern: Group I pattern have an anatomical course of either the right or left coronary artery. In the R-I variant, a very large RCA continues in the atrio-ventricular groove extending to the anterior base of the heart where it gives origin to the anterior descending branch. The L-I pattern occurs when the RCA is congenitally absent and the SCA arising from the left sinus of Valsalva gives off the LAD in the usual fashion and then courses in the atrio-ventricular groove as the LCX, with the RCA arising as a branch from the mid or distal LCX artery

• Group II pattern: The SCA arises from the right or left aortic sinus and the contralateral (be it the LCA or RCA, respectively) arises from the proximal part of the undivided SCA and crosses the base of heart before assuming the normal course of the inherent artery

• Group III pattern: The LAD and LCX artery arise separately from the proximal part of the normal RCA.

The final designation is based on the relationship of course of an anomalous coronary artery to the great vessels (aorta and pulmonary artery): A (anterior to the right ventricular outflow tract); B (between the aorta and pulmonary artery); or P (posterior to aorta).[2,7] Yamanaka and Hobbs modified the Lipton et al. classification of SCA by adding septal (S) and combined (C) types in order to provide more precise description of the anatomical variations. Our patient was classified as L-I subtype of SCA in accordance with the modified Lipton et al. classification. Although SCA is generally considered benign, it has been associated with myocardial infarction, heart failure and sudden cardiac death.[8,9,10] ShiraniandRoberts reported myocardial ischemia in 15% cases of SCA due to the direct consequence of the coronary anomaly.[11]

Yamanakaand Hobbs found that the L-I group of SCA has a benign course.[2] Chou et al. reported that 4 out of 12 patients who had an RCA originating from the distal LCX artery required coronary artery bypass grafts.[12] As the L-I variant of SCA is extremely rare, it is difficult to predict whether patients of this type of coronary artery anomaly are at high risk or benign course. Though most cases are asymptomatic, angina can occur due to acute take-off angles, slit-like orifices, luminal compression by anomalous course between aorta and pulmonary, slow flow and accelerated atherosclerosis. Our patient had only mild atherosclerosis in the proximal LAD with slow coronary flow in the RCA. Therefore, we treated the patient with aspirin, rosuvastatin, ramipril, nicorandil, metoprolol and nitrates.

CONCLUSION

Although SCA is regarded as a benign condition, recognition of this coronary artery anomaly is of paramount importance for interventional cardiologists whenever one confronts the difficulty in identification of both coronary ostia during a coronary angiogram. Considering the rarity of this clinic – anatomical entity, more case reports are needed for better elucidation of the clinical implications of L-I variant of SCA.