Single Right Coronary Artery Continuing as Left Circumflex
Artery and Hypoplastic Left Anterior Descending Artery: A Rare
Coro

Case Report. A 63-year-old female with a history of longstanding diabetes mellitus, hypertension, hyperlipidemia and stable angina presented with recent worsening of exertional angina with rest anginal episodes. She underwent coronary angiography 3 years prior (Figures 1 and 2) for chest pain and it showed an absent left coronary ostia with a single right coronary artery (RCA) continuing as the left circumflex artery (LCX) and a hypoplastic left anterior descending artery (LAD). Her stress cardiac nuclear scan performed at that time showed no reversible ischemia and was being followed up with medications. The patient’s cardiac examination and electrocardiogram (ECG) were normal and her troponin T was negative. The echocardiogram revealed no wall motion abnormalities.
She was treated as an acute coronary syndrome patient and was taken for coronary angiography (Figures 3 and 4), where attempts to cannulate the left coronary artery were unsuccessful. Cannulation of the RCA with a JR4 6-Fr catheter revealed a single coronary artery (SCA) originating from the right sinus of Valsalva at the normal position of the ostium of the RCA.The RCA was large and continued in the right atrioventricular groove, joining the posterior descending artery and posterolateral branch at the crux. The posterolateral branch continued as a large LCX ending in a pouch from which a small hypoplastic LAD tapering proximally was found, but no LAD was seen distally. The aortogram and left ventriculogram showed no vessel arising from the left coronary sinus, and the patient’s left ventricular systolic function was good. Her calculated ejection fraction was 58%. There was no difference between the two angiograms. The patient’s medications were optimized and she is being followed up medically.

Discussion. Congenital coronary artery anomalies are rare occurrences, with an incidence ranging from 0.17% in autopsy studies¹ to 1.3% in angiographic series.² Yamanaka et al studied 126,595 patients over a 28-year period who underwent coronary angiography and found that 1.3% of these patients had a coronary artery anomaly.² The common anomalies described in the literature are: an anomalous circumflex artery originating from a separate ostium in the right sinus of Valsalva or as a proximal branch of the RCA; a RCA arising from the left sinus of Valsalva or as a branch of a SCA; a left coronary artery or LAD originating from the right sinus of Valsalva or as a branch from a SCA, which can have an interarterial course and is associated with sudden cardiac death.
These anomalies are generally asymptomatic, but more potentially serious ones may lead to myocardial ischemia, infarction and/or sudden death. The ideal imaging tool for the diagnosis and delineation of coronary artery anomalies is angiography supported by imaging modalities including computed tomography (CT),³ magnetic resonance imaging (MRI)⁴ and transesophageal echocardiography.⁵ Ropers et al⁶ reported a series of images demonstrating the proximal course of anomalous left main and LAD arteries originating from the right sinus of Valsalva visualized by electron beam CT.
Contrast-enhanced electron-beam CT, multislice spiral and multidetector row CT have been used in delineating the origin and course of anomalous coronary arteries and offer excellent spatial resolution, but use ionizing radiation and potentially nephrotoxic or allergenic contrast agents.
Free-breathing 3-dimensional coronary magnetic resonance angiography⁴ was used in patients to clearly identify anatomy of anomalous coronary arteries because the proximal anatomy was unclear after conventional coronary angiography. MRI holds the greatest appeal because it avoids radiation and contrast agents and yields excellent images. In determining coronary origin, MRI may surpass conventional angiography, especially in patients with congenital defects. Its greatest limitation, however, is its inability to determine the distal coronary course.
The SCA refers to the origination of both the left and right coronary arteries from a single aortic sinus, without the origin of a coronary artery from the pulmonary trunk and has been classified according to different systems.^7–9
SCA is a rare congenital anomaly, and as an isolated finding, occurs in approximately 0.03–0.4% of the population.9 The prevalence of SCA is reported to be < 3% of all major coronary anomalies.²
Smith7 classified the SCA into 3 groups: 1) SCA that follows the course of RCA, then continues into the LCX, which then continues as the LAD, or a single left main artery that branches into LAD and LCX, the latter of which extends across the crux to form the RCA. 2) After its origin, the main trunk divides into the right and left main arteries or into a RCA, LAD and LCX, which then reach their standard locations. 3) The SCA branches so atypically that there is little similarity to the coursing of the three major arteries, as was observed in our patient.
In a study of 142 patients with a SCA, the artery arose from the right aortic sinus in 49% of patients, and from the left aortic sinus in 45% of patients.8 Yamanaka et al reported a SCA arising from the right sinus of Valsalva in 0.019% of the patients in a large series of coronary angiography patients.² In SCAs arising from the right aortic sinus, the left main coronary artery often arises from the proximal part of the common trunk and courses toward the anterior interventricular groove where it divides.
The reported incidence of atherosclerosis in anomalous coronary arteries is variable. Accelerated coronary atherosclerosis may result from acute-angle takeoff malformation.¹⁰ Angina and myocardial infarction are known in the absence of coronary stenosis.¹¹ Coronary arterial spasm is also reported in SCA.¹² Garg et al¹³ examined the presence of atherosclerosis in anomalous coronary arteries and concluded that there does not appear to be an increased risk for the development of atherosclerotic coronary artery disease in anomalous coronary arteries. There are reports of percutaneous angioplasty and stenting in SCA.^10,14
In our patient, a SCA originated from the right sinus of Valsalva that formed the RCA and the posterolateral branch, and continued as the LCX; a hypoplastic LAD was found as well. This abnormality is extremely rare, and the direct continuation of the circumflex artery from the terminal RCA in a SCA was reported only twice previously.^15,16
LAD agenesis has been reported as a benign variant or as a hypoplastic coronary artery that can cause myocardial ischemia.¹⁷ Recently, there was a report of a SCA with an absent LAD associated with an atrial septal defect.¹⁸ Recognition of a SCA is critical because proximal occlusion of the dominant artery could be fatal.
Our case is a unique coronary anomaly in which a SCA continues as a LCX with a hypoplastic LAD. This is a highrisk coronary anomaly and needs close follow up, as occlusion of a SCA would be disastrous to the patient.

References

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