Coronary arteries originating from a single coronary ostium (CO) in the aorta, in the absence of congenital heart disease (CHD), are rare.1 In several large series, the incidence ranged from 0.024% to 0.066%.2–4 In 1979, Lipton et al proposed a classification which, although incomplete, is useful for angiographers.4 The most recent classification by Shirani and Roberts (Figure 1) is solely anatomically based (it takes into account every anatomic probability whether it has been reported or not).1 An ostium originating from the left aortic sinus is type I, and if it arises from the right aortic sinus, it is type II. The most common subtype is IIB: a solitary ostium in the right cusp associated with an aberrant-coursing left main coronary artery (LMCA).1–8 The type I pattern is rarer, with less than 60 cases reported in the literature.1,8–15 We describe here a subtype IB4: a solitary ostium in the left sinus of Valsalva (SV) associated with a right coronary artery (RCA) that arises from the LMCA and courses to the right atrioventricular (AV) sulcus, dorsal to the ascending aorta.1 This constitutes the third case report1,8–15 of a IB4 subtype anomaly. Case Report A 45-year-old male with no significant past medical history was evaluated in the cardiology clinic because of a murmur detected by his primary care physician during a routine physical exam. The examination of the cardiovascular system was unremarkable, and an electrocardiogram was also normal. Transthoracic echocardiography showed a dilated left atrium with mild-to-moderate mitral regurgitation and preserved ejection fraction. Subsequently, the patient underwent a transesophageal echocardiogram which showed a trileaflet aortic valve with mild-to-moderate aortic insufficiency, along with the finding of mild-to-moderate mitral regurgitation. Both valves had only sclerosis, but were otherwise normal. The left atrium was borderline dilated and the interatrial septum was intact. Contrast echocardiography revealed no abnormalities. The aortic root was also normal. Treadmill stress testing also showed good exercise capacity, without ischemic ECG changes. Coronary angiography did not demonstrate any vessel originating from the right coronary cusp, and this was confirmed with an aortic root angiogram (Figure 2). The RCA originated from the left main shortly after its takeoff from the left SV (Figure 3), and it had an aberrant course dorsal to the ascending aorta, continuing on into the right AV sulcus (Figure 4). The coronary system was free of significant atherosclerotic disease. Discussion It is estimated that the incidence of single coronary ostium (CO) without associated congenital heart disease in the general population is less than 1%.9 Due to the influence of embryonic malrotation of the pulmonary infundibular trunk on coronary development, disorders such as tetralogy of Fallot, transposition of the great vessels, common arterial trunk and coronary origin from the pulmonary artery are usually related to a single CO.4 The clinical significance of a single coronary artery is trivial, except for cases in which the LMCA traverses between the pulmonary artery and aortic trunk, which has a higher incidence of sudden death early on in life. Various mechanisms have been proposed to explain this including extrinsic coronary arterial occlusion during exercise, acute kinking of the long LMCA with an associated congenitally small left coronary system, and the acute angle that the right-sided LMCA forms at its origin.4,16–18,19,20 Single left CO is very rare,1–3,9 and whenever present, is the most frequently a type IA anomaly. Type IA is a single coronary artery that divides into the left anterior descending coronary artery (LAD) and the left circumflex coronary artery (LCX). The LCX then courses in the left AV groove to reach the crux, and then continues onward to occupy the anatomic position normally occupied by the RCA.1–3,9–15 When an aberrant-coursing RCA exists, it usually originates from the LMCA and traverses anterior to the right ventricle (Type IB1) or between the pulmonary trunk (Type IB2) and the ascending aorta.1–3 This report details the third documented case of CO anomaly type IB4: a solitary ostium in the left SV associated with a retroaortic-coursing RCA that arises from the LMCA.1–4,8–15 The patient also had a diagnosis of mild-to-moderate mitral and aortic regurgitation, without any other associated anomalies. Nevertheless, transesophageal echocardiography showed sclerosed and thickened aortic and mitral valves, with an appearance resembling rheumatic valvular heart disease, but without any associated congenital malformations. Whenever ischemia is associated with a RCA coming from the left CO, the aberrant course is either anterior to the right ventricle or between the pulmonary trunk and the aortic root.1–3 A retroaortic-coursing RCA has not been associated with clinical significance.1 However, the presence of myocardial ischemia with a retroaortic-coursing LMCA has been reported.18 In that particular case, the functional obstruction was proven with an intracoronary pressure transducer, and the mechanism was thought to be due to diastolic extension of the aortic bulbus and sinus of Valsalva compressing the LMCA.18 Our patient was completely asymptomatic and his exercise stress test was negative for ischemic ECG changes. In conclusion, single coronary ostium anomalies are rare, and when present, have little clinical significance. This is not true when a coronary artery traverses between the pulmonary artery and aorta, which has been linked to sudden death.16–18,19 When having difficulty performing a coronary angiogram, it is important to think of anomalous coronary arteries. When patients with coronary anomalies have significant coronary atherosclerosis, it is important to identify the anatomic location and course of each coronary artery, as damage to the coronary arteries can occur during coronary artery bypass surgery.16
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