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Cardiac Imaging |
1 From the Departments of Radiology (J.D., R.C.A.) and Cardiology (S.K.), Vanderbilt University, Nashville, Tenn; Department of Diagnostic Radiology, University of Maryland School of Medicine, 22 S Greene St, Baltimore, MD 21201 (C.S.W.); Department of Radiology, University Hospital, Cleveland, Ohio (R.C.G.); Department of Radiology, Indiana University School of Medicine, Indianapolis, Ind (C.A.M.); Meharry Medical College, Nashville, Tenn (M.L.J.); and Philips Medical Systems, Cleveland, Ohio (K.R.). Received February 17, 2004; revision requested April 23; revision received July 15; accepted August 18. Address correspondence to C.S.W. (e-mail: cwhite@umm.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Eighteen patients underwent imaging with a four- or 16-section multi–detector row CT unit by using retrospective electrocardiographic (ECG) gating after infusion of 120–150 mL of intravenous contrast material. Section thicknesses of 0.8–3.0 mm were achieved during breath holding, and images were reconstructed with a 50% overlap. Volumetric reconstructions were obtained for each patient. Each study was assessed retrospectively for the origin and course of the anomalous coronary artery by two thoracic radiologists; decisions were made in consensus. Institutional review board exemption and informed consent waiver was granted at each institution. The study was compliant with the Health Insurance Portability and Accountability Act.
RESULTS: Seventeen patients were referred because of equivocal findings at cardiac catheterization or echocardiography; in one, the anomalous coronary artery was incidental. A total of 20 anomalous vessels were found. Twelve patients with 14 variant vessels had an anomalous origin of a left coronary artery (right cusp, 13; noncoronary cusp, one). In four patients, an anomalous right coronary artery originated from the left side; one patient had a single coronary artery arising from the right cusp. In one patient, a left coronary artery-to-vein fistula was observed. In 10 patients, the anomalous vessel passed between the aorta and the main pulmonary artery or right ventricular outflow track. In each case, the origin of the anomalous coronary artery and its course in relationship to the great vessels were unequivocally demonstrated. Volumetric images were useful for showing the three-dimensional orientation of the anomalous coronary artery with respect to the great vessels and cardiac chambers.
CONCLUSION: Multi–detector row CT angiography provided accurate depiction of vessel origin and course in this review of 20 anomalous coronary arteries. The results of this study suggest that CT is a viable noninvasive modality for delineating coronary arterial anomalies, particularly if findings at coronary angiography are equivocal.
© RSNA, 2005
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Conventionally, evaluation of coronary artery anomalies is performed by using catheter-based angiography. However, the precise course of the vessel may not be adequately defined with this technique. Magnetic resonance (MR) imaging has often been used to delineate the anomalous coronary artery in equivocal cases; however, MR imaging can be limited by low spatial resolution and artifacts and can be technically challenging (4). Recently, the development of multi–detector row computed tomography (CT) has permitted better definition of the coronary vessels with CT. Thus, the purpose of our study was to retrospectively determine the imaging features of anomalous coronary arteries depicted at multi–detector row CT angiography in 18 patients seen at four institutions.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Record Review
The medical records were reviewed by the lead investigator at each institution (Vanderbilt University, J.D.; University of Maryland Hospital, C.S.W.; University Hospitals, R.C.G.; Indiana University, C.A.M.). Information was recorded with regard to medical history and whether prior cardiac catheterization or ECG had been performed. In addition, the results of any surgical procedures were noted. The decision as to whether to recommend coronary artery bypass graft surgery was documented. An institutional review board exemption and informed consent waiver was granted for this study at each institution. Our study was compliant with the Health Insurance Portability and Accountability Act.
Imaging
CT scans were obtained in each patient by using four- (n = 11) or 16- (n = 7) section multi–detector row CT scanners (MX8000 or MX8000IDT; Phillips Medical Systems, Best, the Netherlands). For all but one patient, retrospective ECG-gated images were obtained through the heart during one or two breath holds. Details of the scanning protocols for the four- and 16-section CT scanners are provided in Table 1. The average scanning time was 30 seconds, with 3–4 additional minutes for preprocedural placement and adjustment of ECG leads. Reconstructions at various phases of the cardiac cycle were performed. Among patients who underwent ECG gating, the 75% phase during diastole was found to be optimal in the analysis of anomalies of the left coronary artery. Anomalies of the right coronary artery were evaluated at the 37.5%, 50%, or 75% phase of the cardiac cycle, depending on which showed the least amount of motion. Between 120 and 150 mL of iodinated contrast material was injected through an 18–20-gauge intravenous catheter into an antecubital vein at a rate of 3–4 mL/sec. A timing bolus was performed with 20 mL of contrast material, or automated bolus timing was used, as described in Table 1. ß-Blockers were not used to control heart rate.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Twelve patients (14 vessels) had an anomalous origin of a left coronary artery (13 vessels from the right cusp, and one from a noncoronary cusp) (Fig 1). In two of these 12 patients, there were separate anomalies of the left anterior descending and circumflex arteries. Four patients demonstrated an anomalous origin of the right coronary artery from the left side. One patient had a single coronary artery arising from the right cusp (Fig 2). In the last patient, a left coronary artery-to-vein fistula was identified.
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In each case, multi–detector row CT angiography unequivocally demonstrated the origin of the anomalous coronary artery and its course in relation to the great vessels. CT was also effective in delineating the angulation or kinking of the vessel with respect to its point of origin (Fig 3).
Although the transverse images were sufficient to determine the arterial origin and course, reconstructed images provided useful supplemental information. Maximum intensity projection, thin-slab multiplanar reformations, and volumetric images were useful for depicting the three-dimensional spatial orientation of the anomalous vessel with respect to the great vessels and cardiac chambers.
In the patient with the arteriovenous fistula, CT showed the junction between the dilated proximal left circumflex artery and the great cardiac vein, as well as the more normal-appearing left circumflex artery distal to the arterial–venous junction. A volume-rendered image demonstrated the tortuous and ectatic vessel coursing along the posterior surface of the heart (Fig 6). The arteriovenous fistula was presumed to be congenital.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTSDISCUSSIONREFERENCES |
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Approximately 20% of coronary artery anomalies produce life-threatening symptoms, including arrhythmias, syncope, myocardial infarction, or sudden death. Indeed, congenital coronary artery anomalies are the second most common cause of sudden death due to structural heart disease in young athletes (6). In particular, an anomalous vessel that crosses between the aorta and the main pulmonary artery, either a left coronary artery originating from the right sinus or a right coronary artery emanating from the left sinus, may be associated with a poorer outcome (7,8). It is postulated that the acute angulation or slitlike ostium associated with this type of anomaly may lead to myocardial ischemia. During intense physical activity, the aortic wall stretches and dilates to support the increased cardiac output, which further compresses the slitlike ostium of the anomalous vessel against the main pulmonary artery (9). Demonstration of traversal of the coronary artery between the aorta and the main pulmonary artery may be an indication for coronary artery bypass surgery (10). It is important to differentiate an intervascular course, in which the anomalous vessel courses directly between the aorta and the main pulmonary artery, from an intraseptal course, which may appear similar but in which the anomalous vessel passes more inferiorly within the muscular septum. The latter course is associated with a comparatively benign course. CT can often help differentiate these two entities by showing that the anomalous vessel passes within the septal muscle inferior to the plane of the pulmonic valve.
At angiography, the precise course of the anomalous vessel may be difficult to delineate due to its complex three-dimensional geometry displayed in two dimensions fluoroscopically. In the hands of an experienced angiographer, the proper diagnosis can be suggested at cardiac catheterization. The rarity of these anomalies results in limited experience for many angiographers, and this, in turn, causes a large percentage of coronary artery anomalies to be categorized incorrectly at coronary catheterization (11). Thus, noninvasive imaging may prove valuable for confirming the diagnosis.
Noninvasive imaging of the coronary arteries presents substantial obstacles. The proximal coronary vessels measure only 4 mm in diameter, with tapering of the more distal vessels. The arteries are tortuous and are subject to both respiratory and cardiac motion by virtue of their epicardial location. The two major techniques used to noninvasively image the coronary arteries are MR angiography and CT angiography.
Substantial investigative work has been performed with regard to the use of MR imaging and MR angiography in the evaluation of the coronary arteries (12). Multiple two- and three-dimensional strategies have been attempted, but the spatial resolution of the technique has been insufficient to permit its widespread adoption in the setting of atherosclerotic coronary disease. As shown in several studies, MR angiography provides an accurate assessment of the course of anomalous coronary arteries and can be used as an adjunctive technique when results of coronary angiography are equivocal (4,13,14).
Nevertheless, MR imaging has several disadvantages in the assessment of the diminutive coronary arteries. The technique cannot be performed for patients with pacemakers or defibrillating devices, and it may be difficult to perform for claustrophobic patients. MR imaging is best performed with ECG gating, which may not be achievable in patients with certain arrhythmias. Finally, the spatial resolution of MR imaging is substantially inferior to that of the newest generation of CT scanners. Notwithstanding these limitations, MR imaging continues to be a plausible noninvasive alternative for imaging anomalous coronary arteries, as evidenced by a recent MR angiography study with a three-dimensional free-breathing sequence (15).
Early reports of the use of CT for coronary artery evaluation have emphasized electron-beam technology. Ropers et al (16) used ECG-gated electron-beam CT with 3-mm collimation and three-dimensional reconstructions to assess 60 patients, 30 of whom had coronary artery anomalies. Two observers successfully categorized each patient as to the presence or absence of coronary anomalies. Twenty-nine of the 30 anomalies were characterized accurately. Although this study demonstrated the feasibility of CT, electron-beam CT is not widely available and is limited by relatively poor z-axis resolution.
More recently, a number of developments in helical CT technology have substantially enhanced its utility in the evaluation of the coronary arteries (17). Current multi–detector row CT technology, consisting of at least four to 16 detector rows, enables rapid coverage of the coronary territory, generally in a single breath hold. The more rapid coverage permits thinner collimation, often with sections of 1 mm or less. A faster gantry rotation (500 msec or less), combined with the use of partial reconstruction algorithms, has led to more rapid imaging. Currently, a temporal resolution of 50–200 msec is achievable depending on heart rate. With overlapping reconstruction during the cardiac cycle, eight to 10 cardiac phases can be obtained. The better temporal resolution and the ability to choose the optimal cardiac phase result in a near cessation of physiologic motion.
An accurate diagnosis may be achievable, even in the absence of an optimal CT study. As demonstrated with one case in this study, proximal coronary artery images of diagnostic quality may be acquired without ECG gating. Intravenous contrast material was used in each case in this series, but it may not be required to depict coronary anomalies if there is sufficient epicardial fat to provide intrinsic tissue contrast. These issues may be clinically relevant because adequate ECG gating is not possible in all patients, and allergy or renal insufficiency may prevent the use of intravenous contrast material. To date, and to our knowledge, the use of multi–detector row CT in the detection of anomalous coronary arteries has been described only in case reports (18,19).
As demonstrated in the present series, multi–detector row CT angiography was able to delineate clearly the origin and course of the anomalous coronary artery. In no case was the proximal course of the coronary vessel ambiguous. In general, the entire study, including lead placement, was completed within 5 minutes, which is substantially faster than is typically achieved with MR imaging. The small section thickness permitted volumetric reconstructions of high quality. Although these images were not crucial in the diagnosis of the anomaly, they were valuable for depicting the relationships among the coronary vessel, great vessels, and ventricles. Such images give the surgeons a better understanding of the complex anatomy before repair.
An important consideration is the high effective radiation dose (9 mSv) to which a patient undergoing multi–detector row CT angiography is exposed. By comparison, the estimated radiation dose with electron-beam CT and diagnostic coronary arteriography is 1–2 mSv and 3–10 mSv, respectively (20,21). Although the radiation dose is of concern, investigators have shown the potential to substantially decrease the radiation exposure with multi–detector row CT angiography by reducing the dose during the systolic portion of the cardiac cycle (22).
Our study is limited both by its retrospective nature and a relatively small number of patients. Another drawback is the lack of a reference standard technique to prove that our consensus CT findings were correct. In all but two of our patients, an equivocal coronary angiogram, the purported reference standard, was the stated indication for CT. Although direct visualization at surgery is confirmatory, the anomalous coronary course is often obscured by epicardial fat (Cardarelli M, oral communication, 2004). Thus, surgery cannot be considered a consistently reliable standard reference technique. Because of the indeterminate coronary angiogram and lack of an external reference standard, a direct comparison between multi–detector row CT angiography and coronary angiography was not possible.
In the present series, multi–detector row CT angiography provided accurate depiction of vessel origin and course in this review of 20 anomalous coronary arteries. Most patients were referred after an equivocal coronary angiogram. The results of this study suggest that CT is a viable noninvasive modality in the delineation of coronary arterial anomalies, particularly if results of coronary angiography are equivocal.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, C.S.W.; study concepts and design, J.D., C.S.W., R.C.G., C.A.M.; literature research, C.S.W.; clinical studies, J.D., C.S.W., R.C.G., C.A.M.; data acquisition, J.D., C.S.W., R.C.G., C.A.M., K.R.; data analysis/interpretation, all authors; statistical analysis, C.S.W.; manuscript preparation, all authors; manuscript definition of intellectual content, J.D., C.S.W., R.C.G., C.A.M.; manuscript editing and revision/review, all authors; manuscript final version approval, J.D., C.S.W., R.C.G., C.A.M.
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