Single coronary ostium is a very rare congenital anomaly with an incidence of 0.024% in angiographic series. This is the third case of Shirani-Roberts subtype IB4: solitary ostium in the left coronary sinus associated with a retroaortic-coursing right coronary artery that arises from the left main coronary artery. The patient is a 45-year-old male with no past medical history, and who was seen in the clinic for evaluation of a murmur. Echocardiography showed rheumatic heart disease with mild mitral regurgitation and moderate aortic regurgitation; no shunts were present. Coronary and aortic root angiography did not show a vessel originating from the right coronary cusp. The right coronary artery originated from the left main coronary artery and had an aberrant course which was dorsal to the ascending aorta. No associated congenital heart disease was present.

       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

Figure 1

Shirani and Roberts classification. Diagram displaying the most frequent subtypes IIB1–IIB4. It also shows anomaly IB4, subject of this case-report.

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

Figure 3

Right anterior oblique view showing the aortic root angiogram with no vessel originating from the right coronary cusp.

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

Figure 2

Right anterior oblique view showing the aortic root angiogram with no vessel originating from the right coronary cusp.

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.

Figure 4

Left anterior oblique cranial view showing the right coronary artery with an aberrant course dorsal to the ascending aorta, continuing on into the right atrioventricular sulcus.

       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

1. Shirani J, Roberts WC. Solitary coronary ostium in the aorta in the absence of other major congenital cardiovascular anomalies. J Am Coll Cardiol 1993;21:137–143.
2. Desmet W, Vanhaecke J, Vrolix M, et al. Isolated single coronary artery: A review of 50,000 consecutive coronary angiographies. Eur Heart J 1992;13:1637–1640.
3. Lipton MJ, Barry WH, Obrez Y, et al. Isolated single coronary artery: Diagnosis, angiographic classification, and clinical significance. Radiology 1979;130:39–47.
4. Kuon E, Ropers D. Single coronary artery – A rarity in the catheterization laboratory: Case report and current review. Can J Cardiol 2004;20:647–651.
5. Ozeren A, Aydin M, Bilge M, Cam F. Anomalous left coronary artery arising from the right sinus of Valsalva: A case report. Int J Cardiol 2005;101:491–493.
6. Yasar B, Gorenek B. A rare coronary artery anomaly: Origin from the single ostium. Anadolu Kardiyol Derg 2004;4:106.
7. Mavi A, Sercelik A, Ayalp R, et al. Single coronary artery arising from the right sinus of Valsalva (case report). Okajimas Folia Anat Jpn 2002;79:163–167.
8. Chan CN, Berland J, Cribier A, Letac B. Angioplasty of the right coronary artery with origin of all three coronary arteries from a single ostium in the right sinus of Valsalva. Am Heart J 1993;126:985–987.
9. Hernandez F, Garcia Tejada J, Pindado C, Tascon JC. Single coronary artery and right coronary ostium agenesis. Rev Esp Cardiol 2000;53:1398
10. Shammas RL, Miller JM, Babb JD. Single left coronary artery with origin of the right coronary artery from distal circumflex artery. Clin Cardiol 2001;24:90–92.
11. Garbo R, Steffenino G, Russ P. The single coronary artery, two clinical cases. Ital Heart J Suppl 2000;1:262–265.
12. Ayala F, Badui E, Murillo H, et al. Right coronary ostium agenesis with anomalous origin of the right coronary artery from an ectasic circumflex artery. A case report. Angiology 1995;46:637–639.
13. Mavi A, Sercelik A, Ayalp R, et al. Single coronary artery arising from the left sinus of Valsalva. Saudi Med J 2002;23:1537–1540.
14. Gowda RM, Khan IA, Undavia M, et al. Origin of all major coronary arteries from left sinus of Valsalva as a common coronary trunk: Single coronary artery — A case report. Angiology 2004;55:103–105.
15. Lo EA, Dia A, Ouedraogo T, et al. A propos of a case of solitary left coronary artery. Dakar Med 1990;35:220–225
16. Neil DAH, Bonser RS, Townend JN. Coronary arteries from a single coronary ostium in the right coronary sinus: A previously unreported anatomy. Heart 2000;83:e9.
17. Kragel AH, Roberts WC. Anomalous origin of either the right or left main coronary artery from the aorta with subsequent coursing between aorta and pulmonary trunk: Analyses of 32 necropsy cases. Am J Cardiol 1988;62:771–777.
18. Ozeren A, Aydin M, Bilge M, Cam F. Anomalous left coronary artery arising from the right sinus of Valsalva: A case report. Int J Cardiol 2005;101:491–493.
19. Schwarz ER, Hager PK, Uebis R, et al. Myocardial ischaemia in a case or a solitary coronary ostium in the right aortic sinus with retroaortic course of the left coronary artery: Documentation of the underlying pathophysiological mechanisms of ischaemia by intracoronary Doppler and pressure measurements. Heart 1998;80:307–312.
20. Yamanaka O, Hobbs RE. Coronary artery anomalies in 126,595 patients undergoing coronary arteriography. Cathet Cardiovasc Diagn 1990;21:28–40.