Coronary Artery Imaging: Clinical Results

Identification of Anomalous Coronary Arteries

As discussed in Chapter 23 , using current whole-heart imaging with or without gadolinium contrast, the native proximal coronary arteries can be reliably visualized in nearly all subjects. Although unusual (<1% of the general population ) and most often benign, congenital coronary anomalies in which the anomalous segment courses anterior to the aorta and posterior to the pulmonary artery are well-recognized causes of myocardial ischemia and sudden cardiac death in children and young adults. These adverse events commonly occur during or immediately after intense exercise and are believed to be related to compression of the anomalous segment, vessel kinking, or coexistent eccentric ostial stenoses.

The ability of coronary artery CMR to reliably identify the major coronary arteries and their relationship to the ascending aorta and pulmonary artery immediately provides for its application for the identification and characterization of anomalous CAD. The spatial resolution requirements for identifying anomalous coronary vessels are less stringent than for defining native vessel stenoses, allowing for lower resolution and faster CMR imaging.

Projection x-ray angiography had traditionally been the imaging test of choice for the diagnosis and characterization of these anomalies. However, the presence of an anomalous vessel is sometimes suspected only after the procedure, particularly in a situation in which there was unsuccessful engagement of a coronary artery. In addition, the uncommon use of a pulmonary artery catheter has made characterization of the anterior or posterior trajectory of the anomalous vessels more difficult to appreciate on projection x-ray angiography.

Coronary artery CMR has several advantages compared with both coronary MDCT and x-ray angiography in the diagnosis of these coronary anomalies. In addition to being noninvasive and not requiring ionizing radiation or iodinated contrast agents, coronary artery CMR provides a definitive three-dimensional (3D) “road map” of the mediastinum ( Fig. 24.1 ). Early studies applied two-dimensional (2D) breath-hold segmented k -space gradient echo coronary artery CMR, although most centers now use targeted 3D or whole heart free-breathing navigator coronary artery CMR because of the superior reconstruction capabilities afforded by 3D datasets, with similar results. The ability to acquire these data using CMR without the use of ionizing radiation is likely to be of particular benefit in the generally younger population.

In addition, noncontrast coronary artery CMR is likely preferred to avoid potential long-term issues related to retention of gadolinium.

There have been at least eight published series of patients who underwent a comparison of coronary artery CMR at 1.5 T or 3 T with x-ray angiography for suspected anomalous CAD. These studies have uniformly reported excellent accuracy, including several instances in which coronary artery CMR was determined to be superior to x-ray angiography ( Table 24.1 ). Data also suggest coronary artery CMR evidence of a coronary anomaly carries important prognostic information with the identification of the anomalous segment originating from the opposite sinus of Valsalva (see Fig. 24.1 ) as conveying an adverse prognosis. As a result, CMR is considered a class I indication for suspected anomalous CAD. At experienced CMR centers, clinical coronary artery CMR is the preferred test for patients in whom anomalous disease is suspected, those with known anomalous disease that must be further clarified, and those with coronary anomalies associated with other cardiac anomalies (e.g., tetralogy of Fallot). Although MDCT has also been shown to be efficacious for this indication, coronary artery CMR is often preferred because there is no need for ionizing radiation or intravenous contrast.

Coronary Artery Aneurysms and Kawasaki Disease

Coronary artery aneurysms are relatively uncommon, but have received increasing attention because of their common occurrence in pediatric and young adult patients with a history of mucocutaneous lymph node syndrome (Kawasaki disease), a generalized vasculitis of unknown etiology usually occurring in children age >5 years. The prevalence of Kawasaki disease is highest among children of East Asian countries, with the greatest prevalence in Japan. Infants and children with this syndrome may show evidence of myocarditis or pericarditis, with nearly 20% having coronary artery aneurysms. These aneurysms ( Fig. 24.2 ) are the source of both short-term and long-term morbidity and mortality. Fortunately, one-half of the children with coronary aneurysms during the acute phase of the disease have a normal-appearing coronary lumen on catheter-based x-ray angiography 2 years later. Transthoracic echocardiography is often adequate for diagnosing and following these proximal and mid-vessel aneurysms in very young children, but this modality is deficient after adolescence and in obese children. These young adults are therefore often referred for serial catheter-based x-ray coronary angiography, with the accumulation of significant radiation exposure over time. Coronary artery CMR data from two series of adolescents and young adults with coronary artery aneurysms have confirmed the high accuracy of coronary artery CMR for both the identification and the characterization (diameter and length [ Fig. 24.3 ]) of these aneurysms with addition of cine ventricular function and late gadolinium enhancement (LGE) for a comprehensive cardiac assessment. Although not specifically examined in long-term follow-up studies, these data suggest that coronary aneurysms can now be effectively followed with serial CMR studies, including vessel wall inflammation. Similar data have been reported for ectatic coronary vessels.