Diagnostic modalities for the evaluation of anomalous left main coronary arteries

1. Introduction 

Anatomic aberrations of the coronary arteries are observed in approximately 1% of the population, with the majority being incidentally discovered during cardiac catheterization [1]. The clinical significance of these anomalies depends not only on the site of origin, but also on its anatomical course. The diagnosis of an anomalous coronary artery and defining its course is of great importance, given the potential clinical implications for certain variants. For instance, an interarterial (between aorta and pulmonary artery) course of an anomalous coronary artery has been associated with a significant increase in the risk of angina, syncope, or even sudden death [2], [3]. The refinements in noninvasive techniques such as transesophageal echocardiography, computed tomographic (CT) angiography, and cardiac magnetic resonance imaging (MRI) have allowed for the identification of these vessels and their courses. We present 3 cases of an anomalous left main coronary artery (LMCA) that arises from the right sinus of Valsalva. Various noninvasive diagnostic imaging modalities were used to define its anatomic course.

2. Case 1 

A 48-year-old Caucasian woman with a history significant for an unknown congenital heart defect repaired at age 11 years was admitted to the hospital for increasing shortness of breath, ultimately requiring mechanical ventilation. As part of the work-up to investigate the etiology of her respiratory failure, a transthoracic echocardiogram was performed. Using a Hewlett Packard 5500 ultrasound system, left ventricular hypertrophy with a subaortic membrane and a left ventricular ejection fraction of 65% was noted. Additionally, there appeared to be a large anomalous coronary artery coming off the right semilunar cusp of the aortic valve. Given these findings, a transesophageal echocardiogram (TEE) was performed, which confirmed the presence of a large subaortic membrane (mean pressure gradient of 45 mmHg and a peak gradient of 85 mmHg), in addition to a surgical patch over the membranous septum at the level of the left ventricular outflow tract, suggesting the presence of a prior repair. Furthermore, a large common coronary trunk giving origin to the left and right coronary arteries was noted to arise from the right coronary sinus of Valsalva and course posteriorly behind the aorta (Fig. 1). After extubation, the patient underwent cardiac MRI, which also visualized the coronary anomaly (Fig. 2). This anatomy was confirmed by coronary angiography (Fig. 3).

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Fig. 1. Case 1. TEE demonstrating a common coronary artery trunk (arrowhead) arising from the right sinus of Valsalva (A) with the LMCA (arrowheads) coursing posteriorly behind the aorta (B). AV=aortic valve; LA=left atrium; RA=right atrium; RV=right ventricle.

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Fig. 2. Case 1. Coronal section. MRA (gradient echo image) revealing anomalous origin of the LMCA. Ao=aorta; LA=left atrium; LAD=left anterior descending artery; LCx=left circumflex artery; LMCA=left main coronary artery; RA=right atrium; RVOT=right ventricular outflow tract.

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Fig. 3. Case 1. Left anterior oblique projection. Coronary angiogram depicting the common coronary artery trunk (CCI) giving rise to the right coronary artery (RCA) and the LMCA. Please see Fig. 2 for abbreviations.

The patient was referred to cardiovascular surgery for repair of the left ventricular outflow tract obstruction and aortic root. A detailed finding of the coronary anatomy was relayed to the surgeons to ensure that these vessels would not be inadvertently injured during surgery. The patient did not undergo concomitant coronary artery bypass grafting due to the noninterarterial course.

3. Case 2 

A 39-year-old African-American man, with a history of tobacco and cocaine abuse, was admitted with a 2-day history of substernal, nonradiating chest pressure. Chest X-ray and electrocardiographic examination was unremarkable. Serial cardiac biomarker measurements were elevated. A cardiac catheterization was performed revealing an anomalous takeoff of the LMCA from the right aortic sinus of Valsalva. With a pulmonary artery catheter in place, it appeared that the LMCA coursed between the aorta and the pulmonary trunk (Fig. 4). There was otherwise no evidence of obstructive coronary artery disease. A CT scan of the chest with intravenous contrast confirmed the anomalous takeoff and course (Fig. 5). Consequently, coronary artery bypass grafting was performed using a left internal mammary arterial graft to the left anterior descending coronary artery. The procedure was uneventful, and the patient was discharged in stable condition.

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Fig. 4. Case 2. Coronary angiogram with pulmonary artery (PA) catheter in position revealing anomalous LMCA coursing between the aorta and pulmonary artery (interarterial course). Please see Fig. 2 for abbreviations.

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Fig. 5. Case 2. Axial image chest CT (4-slice MDCT) with contrast demonstrating an interarterial course of the anomalous LMCA from the right sinus of Valsalva. PA=pulmonary artery. Please see Fig. 2 for remaining abbreviations.

4. Case 3 

A 58-year-old African-American woman with Type 2 diabetes mellitus, hypertension, former tobacco abuse, and asthma presented for elective cardiac catheterization for further evaluation of disabling angina. She reported a 1-year history of intermittent, nonradiating substernal chest tightness with associated dyspnea. There were no identifiable precipitating factors. The electrocardiogram was nondiagnostic. Cardiac catheterization revealed an anomalous origin of the LMCA coming off the right coronary cusp, sharing an ostium with the right coronary artery (RCA). Using a pulmonary artery catheter, angiography showed that the LMCA appeared to course between the aorta and the pulmonary artery. The coronary arteries were otherwise angiographically normal. The left ventricular ejection fraction was approximately 55%. A chest CT using intravenous contrast confirmed the abnormal anatomy of the coronary arterial system (Fig. 6). The patient underwent coronary artery bypass surgery with a left internal mammary arterial graft to the left anterior descending coronary artery. The patient was discharged home on the fifth postoperative day.

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Fig. 6. Case 3. Axial image chest CT with contrast demonstrating an interarterial course of the LMCA. PA=pulmonary artery. Please see Fig. 2 for remaining abbreviations.

5. Discussion 

We present 3 cases of an anomalous takeoff of the LMCA. In the latter 2 cases, the LMCA was coursing between the aorta and the pulmonary artery. This anomaly is the least frequent among coronary anomalies but carries serious prognostic implications, with sudden death occurring up to 27% of cases [4]. It has been reported that high-risk anatomy involves abnormalities of the initial coronary artery segment or coursing of the anomalous artery between the pulmonary artery and aorta [5]. Sudden and exercise-related death has been mainly associated with the origin of the LMCA from the right coronary sinus [6]. The mechanism of sudden death is not fully explained, but may be due to compression of the LMCA between the distended aorta and pulmonary artery during exertion [4]. However, this theory has fallen out of favor, given that the pressure in the arterial system is significantly higher during diastole than the pressure in the pulmonary circulation. A more commonly accepted explanation is the “kinking” of LMCA during increased flow through both the aorta and the pulmonary artery [7]. A slit-like orifice of the anomalous LMCA, intramural course of the proximal vessel, coronary vasospasm, and replacement-type fibrosis have also been described as potential etiologies causing myocardial ischemia and ventricular tachyarrhythmias.

Coronary angiography remains the gold standard for the identification of anomalous coronary arteries and their course. However, recent technological advances have provided noninvasive alternatives for the assessment of these anomalies with similar, if not better, accuracy. Coronary magnetic resonance angiography (MRA) is a very useful imaging modality and may eventually replace coronary angiography as the gold standard for detecting coronary artery anomalies [8], [9], [10]. Nonetheless, MRA is occasionally limited by the ability to achieve adequate “gating” for image acquisition, and the image quality is such that the middle and distal coronary segments cannot be reliably visualized [11]. This is especially difficult given the constant motion of the heart during the cardiac cycle and respiration.

Multidetector row computed tomography (MDCT) coronary angiography is another evolving technique that allows for better temporal and spatial resolution compared to MRA [12]. Currently, 4- and 16-slice systems are mainly in use. 64-slice systems are currently being evaluated for coronary CT angiography use. It still requires gated acquisition of the image and the administration of 100–150 ml of intravenous contrast for satisfactory images. Potential shortfalls to high-quality image acquisition and interpretation are the presence of calcified segments, motion and noise artifact, and overlying vessels that limit adequate image interpretation (i.e., great cardiac vein obscuring coronary segments) [13], [14]. Both MDCT and MRA have the capability of three-dimensional reconstruction of the image for better delineation of the coronary anatomy.

Transesophageal echocardiography has been proposed by some investigators as a reliable method for detecting anomalous origins of coronary arteries. In one study, all 11 patients described had adequate images of the origin of the LMCA, while the RCA proved to be more challenging [15]. Doppler evaluation of the coronary flow is an advantage for TEE over other noninvasive modalities, although this is operator dependent and requires a high level of skill. The inability to evaluate the middle and distal segments of the coronaries is a significant limitation of TEE. Given the better image quality of MRA and MDCT, the use for a more invasive approach, such as transesophageal echocardiography, is of limited utility in the assessment of anomalous coronary arteries.

In conclusion, the ability of noninvasive imaging modalities to reliably detect and characterize coronary anomalies is an asset in the practitioner's diagnosis armamentarium and allows for better patient management. Futhermore, the unique nature of the information provided by each modality suggests that these techniques are best considered as complementary rather than exclusive alternatives.