Anomalous Right Coronary Artery Originating From the Mid Left Anterior Descending Artery: A Rare Coronary Anomaly

Coronary artery anomalies can be associated with myocardial ischemia and sudden cardiac death. However, many patients with coronary anomalies are asymptomatic, and are diagnosed incidentally by coronary angiography or by coronary CT angiography.¹ Coronary artery anomalies can be found in up to 1.3% of patients undergoing coronary angiography, as reported by a large retrospective series.² Anomalous origin of the right coronary artery is a rare congenital anomaly and was first described in 1948 by White and Edwards.³ Single coronary artery, where both the right and left coronary arteries originate from a common aortic sinus, is exceedingly uncommon, occurring in between 0.008% and 0.067% of those referred for angiography.⁴ An extremely rare variant of this anomaly is origin of the right coronary artery (RCA) from the left anterior descending artery (LAD). We report here the case of a 33-year-old woman who presented with syncope and was found to have an anomalous RCA arising from the mid portion of the LAD.

Case

A 33-year-old African American female with a history of depression, chronic migraine headaches, and asthma presented to the cardiology clinic for further evaluation of syncope. She reported three episodes of frank syncope preceded by symptoms of dizziness and light-headedness, with each episode lasting anywhere from five to thirty minutes. Up to this point, her activity level was normal. Family history was notable for premature coronary artery disease (CAD) in her father, but otherwise negative for sudden cardiac death. Her only medications included an albuterol inhaler. She was hemodynamically stable on examination without evidence of orthostasis. Her physical examination was normal. Her body mass index (BMI) was 27.7 kg/m². An electrocardiogram (ECG) revealed sinus rhythm with sinus arrhythmia without further abnormalities, including a normal QTc interval. A transthoracic echocardiogram (TTE) showed normal left ventricular size and systolic function (ejection fraction 55-60%), and normal right ventricular size and function with no valvular abnormalities. She underwent three-day Holter monitoring, which revealed no sustained arrhythmias. She also underwent a neurologic workup, including a computed tomography (CT) angiography of the head/neck and an electroencephalogram, in order to rule out seizures or other neurologic etiology of her symptoms. Both studies were normal.

Given her history of recurrent syncope, she was referred for coronary CT angiography. She was given beta-blockers and sublingual nitroglycerin, and underwent prospectively gated coronary CT angiography (Siemens SOMATOM Definition Flash). The study revealed a congenitally absent RCA, with a single coronary originating from the left sinus of Valsalva. There was a discrete branch, arising from the mid portion of the LAD and coursing anteriorly to the right ventricle that served as the right coronary artery (Figure 1). The anomalous RCA was coursed along the right ventricular free wall, anteriorly to the pulmonary trunk. Of note, there was a paucity of vascular supply to the right ventricular free wall as well as the posterior surface of the right ventricle. Importantly, there was no evidence of other concomitant congenital anomalies such as tetralogy of Fallot. The patient subsequently underwent a nuclear stress perfusion study that revealed a mild, reversible perfusion defect involving the basal inferior wall, corresponding to the RCA distribution (Figure 2, Video 1). Coronary angiography confirmed a single coronary ostium with the left main coronary artery bifurcating into the LAD and the left circumflex artery with a left dominant system. There was anomalous origin of the RCA from the mid portion of the LAD. The distal RCA and right posterior lateral segment (RPLS) received collateral flow from the left circumflex artery. Multiple aortic root injections confirmed the absence of a conventional right coronary artery originating from the right sinus of Valsalva (Figure 3, Video 2). The patient subsequently underwent an electrophysiology study that showed no evidence of inducible arrhythmias. The patient was referred for an implantable loop recorder for longer term arrhythmia monitoring. Given her lack of arrhythmia and negative neurological workup, her syncope was thought to be related to the coronary anomaly. She was advised on moderate exercise to help with coronary conditioning and development of collaterals. She is currently asymptomatic on metoprolol succinate 50 mg daily. At follow-up six months after hospitalization, she was without additional syncopal or pre-syncopal episodes.

Discussion

We described a case of a young female who presented with syncope and was found to have an extremely rare variant of an anomalous RCA arising from the mid LAD. In a retrospective study by Yamanaka and Hobbs that included 126,595 patients undergoing coronary angiography, the incidence of coronary artery anomalies was 1.3%, with an anomalous RCA originating from the left sinus of Valsalva in 0.1%.² There were no identified cases of an anomalous RCA originating from the mid left anterior descending artery in this review.² Lipton et al described a useful angiographic classification scheme to identify anomalous coronary arteries based on their site of origin and anatomic distribution.⁵ The anomalous artery is further classified into the “R” or “L” subtypes depending on whether the ostium originates from the right or left sinus of Valsalva. Each type is designated into three groups (I, II, III) depending on the anatomical course of the artery (Table 1). Lastly, a designation was established between the anomalous artery and its relationship to the aorta and pulmonary artery (anterior [A], posterior [P], and in-between [B] patterns).

Our patient’s coronary artery anomaly does not fall easily into any of these categories, presumably because there were no identified variants of this kind, further confirming the rarity of this anatomic entity. Under this schema, the closest category that our patients’ coronary anatomy represented was that of the LIIA anomaly. In the review by Yamanaka and Hobbs, 11 patients were noted to have LIIA anomalies (incidence of 0.0009%).² However, other reported series have considered an LIIA anomaly to include an RCA that originates as a branch of the LAD.⁶ In a 2012 review, less than 30 cases were identified with this anomaly in the literature, with a majority being males (65%) and only four patients were below the age of 40 upon diagnosis.⁷ Although the use of taxonomy may obfuscate the reported cases of this entity, the literature still clearly reports this to be an extremely rare coronary artery anomaly.

The clinical significance of coronary artery anomalies varies and is related to their anatomic course. Many of these anomalies are found as incidental findings and often remain asymptomatic. However, some variants may present with symptoms of exertional angina, dyspnea, palpitations, syncope, ventricular fibrillation, myocardial infarction, and sudden cardiac death, especially following exercise.^7-9 These symptoms have been most notably reported with a coronary artery originating from the pulmonary artery and a single coronary artery originating from the left or right sinus of Valsalva with an inter-arterial course.⁹

The clinical significance of an anomalous RCA arising from the mid LAD is unknown. A review by Wilson et al suggests a benign course, without increased incidence of coronary artery disease (CAD).⁴ However, there are also conflicting reports by Yamanaka and Hobbs characterizing a single coronary artery as a potentially malignant variant, along with ectopic origin from the pulmonary artery or from the opposite sinus, not traveling between the great vessels, and coronary artery fistulae.² There are reports of increased susceptibility to CAD in patients with an anomalous RCA.^8,9 However, the overall correlation between CAD and coronary anomalies remains uncertain.¹⁰ Coronary arteries with an abnormal origin and course have been considered to be more prone to atherosclerosis.^7,11 The exact pathophysiologic basis for angina, myocardial infarction, and sudden death is unclear. One proposed mechanism involves mechanical compression of the anomalous artery between the aorta and pulmonary root/great vessels, especially with exercise.^2,5,12 Other high-risk features include presence of coronary vasospasm, an acute angle of takeoff, a slit-like orifice, and intramural course.^7,10 Taylor et al, in their study of 242 autopsy patients with isolated coronary artery anomalies, identified cardiac death in 142 cases (59%), with sudden death occurring in 78 cases (32%).¹³ They further noted that amongst sudden cardiac deaths, 45% occurred with exercise. Among those with an anomalous origin of the RCA, 25% died suddenly and in most cases were asymptomatic. The anomaly was also found to be commonly associated with exercise-related death (46%). In all cases, exercise consisted of aerobic activity (running, marching, calisthenics, basketball, and soccer).

Our patient reported a marked decrease in exercise tolerance. It is possible that her decreased functional capacity and syncope were related to diminished vascular supply to the RCA territory. Her nuclear stress perfusion study demonstrated mild reversible perfusion deficits in the basal inferior wall, corresponding to the RCA distribution. Given her unremarkable electrophysiologic studies and bland neurologic workup, it is not likely that her syncope was attributable to an arrhythmia or a neurologic cause. Despite the benign anterior course of her anomalous coronary artery, it is conceivable that the paucity of vascular supply to her RCA distribution was responsible for her symptoms.

There are a number of diagnostic modalities that are helpful for the evaluation of anomalous coronary arteries, including echocardiography, invasive coronary angiography, coronary CT angiography, and magnetic resonance angiography (MRA). Coronary angiography has traditionally been the gold standard in detection of diseases such as CAD and coronary vessel anomalies, but detection of three-dimensional anatomy can be difficult. Additionally, it may be difficult to selectively cannulate anomalous vessels and identify their course. Coronary CT angiography has multiple benefits, including high spatial resolution, rapid examination time, and the ability to provide complementary three-dimensional information.^7,10,14 Coronary MRA can also be useful, particularly in identifying the proximal course of anomalous coronary arteries.¹⁵ However, coronary CT angiography provides superior spatial resolution, with the ability to track the distal course of anomalous vessels with high accuracy.

In symptomatic patients with anomalous coronary arteries and documented myocardial ischemia or ventricular tachyarrhythmias, surgical intervention is indicated. In asymptomatic patients, the management is less clear. Many centers refer patients with an intramural course of the anomalous vessel for surgery.^16,17 Surgical intervention can include coronary artery bypass grafting, or “unroofing” or marsupialization of the anomalous vessel.¹⁸ However, it is less clear what the surgical options are in the case of the RCA originating from the mid LAD. Despite the lack of data, there is agreement that patients with anomalous coronary arteries be closely screened for ischemia and tachyarrhythmias, and counseled about physical activity, as many cases of sudden cardiac death are related to exercise and aerobic activity.

Conclusion

An anomalous RCA originating from the mid-LAD is truly a rare entity, with very few cases reported in the literature. We report here an interesting case of the RCA originating from the mid LAD, resulting in paucity of vascular supply to the right ventricle and myocardial ischemia on perfusion imaging. Although there is no clear data regarding management of this extremely rare variant of anomalous coronary artery, careful screening for ventricular tachyarrhythmias and exercise counseling should be conducted. This case highlights the utility of multimodality imaging, including invasive coronary angiography, coronary CT angiography, electrophysiologic testing and perfusion imaging in detecting an exceedingly rare clinical entity. 

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