Congenital absence of right coronary artery without any other associated anomalies

Presentation

A 61-year-old female was referred to cardiology clinic for evaluation of atypical chest pain. She has history of chronic smoking, hypercholesterolemia, hypertension, and anxiety, and had been complaining of vague right-sided chest discomfort. Exercise Thallium perfusion scanning revealed a less than 10% reversible defect in the anteroapical region of the left anterior descending artery (LAD) territory. Due to her risk factors and a positive nuclear stress test, she was sent for cardiac catheterization.

Evaluation and diagnosis

Coronary angiography demonstrated a normal looking LM coronary artery giving rise to LAD and a large caliber left circumflex (LCx). The left anterior descending artery was normal and the LCx showed mild luminal irregularities. The distal LCx continued beyond the atrioventricular groove into right coronary artery territory to terminate close to base of the heart. We were unable to find the ostium of the RCA using a Judkins RCA 4.0 catheter. Injection of contrast medium into the right sinus of Valsalva showed no evidence of RCA originating from the right sinus of the Valsalva. There was no significant stenosis in any of the coronary arteries (Figures 1-3).

Figure 1. Coronary angiogram of left coronary tree

showing continuation of distal left circumflex artery in

right coronary artery territory.

Discussion

Coronary anomalies are relatively common, with a reported incidence of 0.2% to 1.3% in the general population. ^1,2,11 Most anomalies are clinically insignificant; however, some anomalies have been associated with adverse outcomes like angina, dyspnea, syncope, acute myocardial infarction, and even sudden death. Clinicians face the challenge of precisely identifying these anomalies associated with adverse outcomes. In this context, recognition of an anomalous origin of the coronary artery from the opposite sinus is particularly relevant due to the significantly increased mortality rate for an anomalous left coronary artery arising from the right sinus (57%) and RCA arising from the left sinus (25%).¹²

Single coronary arteries are very rare, with an autopsy incidence of 0.29%.² Forty percent of the anomalies occur in association with other congenital cardiac abnormalities.³ An RCA originating from the LM coronary artery accounts for only 0.65% of these anomalies.¹ Congenital absence of RCA has been described previously in a 38-year-old female with nonobstructive hypertrophic cardiomyopathy where RCA arose as an extension of terminal portion of LCx¹³ and in another 78-year-old female with obstructive hypertrophic cardiomyopathy where RCA arose as an extension of terminal portion of LAD.¹⁴ McMahon at al¹⁵ reported atresia of the proximal RCA in a 2-year-old boy that was associated with fistula from LAD to mid portion of the RCA. Our case represents first reported congenital absence of RCA without associated structural cardiac abnormalities.

Figure 2. Aortogram showing absence of origin of right

coronary artery.

Right coronary artery anomalies are of controversial significance. Virmani and associates found that in 21 patients with this anomaly, 10 died of cardiac causes, of which 5 were sudden (eg, 4 with no signs of atherosclerosis).¹⁶ There are 2 mechanisms of ischemia that have been proposed for these anomalies. The great vessels, which dilate during exercise, may externally compress the coronary artery.^5-6 The second proposed mechanism suggests that valve-like ridges and the acute angulation of the artery as it traverses from the left to the right sinus may induce ischemia.⁶

In this case of absent RCA, the dominant LCx supplied the RCA territory. Since the left coronary artery assumed abnormal course, there was no concern for abnormal external compression causing ischemia. Due to the absence of coronary obstruction, the 10% anteroapical defect noted on perfusion imaging was attributed to a false positive test. Patient was reassured and advised for risk factor modification.

Figure 3. Coronary angiogram showing distal left

circumflex artery in right coronary artery territory.

In conclusion, congenital absence of RCA is a rare finding. At the current time, diagnosis of congenital coronary anomalies is made by coronary angiography. In the future noninvasive modalities including electrocardiographic-gated multidetector computed tomography (MDCT)⁷ and magnetic resonance imaging can also be used to make a definitive diagnosis.