According to the World Health Organization, coronary artery disease (CAD) is one of the leading causes of death worldwide, accounting for 17 million deaths per year. Although it was once considered a “western disease,” today more than 60% of cases occur in developing countries.

While a number of non-invasive diagnostic tests, such as nuclear scanning and echocardiography, provide valuable information about the heart and coronary arteries, the gold standard for the detection and evaluation of CAD is coronary angiography, which is performed nearly 1.5 million times a year in the U.S. Despite its undisputed clinical value, coronary angiography is costly, invasive, and poses some risks, therefore it is indicated only for patients determined to be at high risk for CAD.

A NON-INVASIVE ALTERNATIVE
Because early detection and treatment of CAD can significantly reduce morbidity and mortality, there has been an ongoing, widespread interest in finding a non-invasive alternative to coronary angiography that is equal to, if not better than, the current gold standard. The modality showing the greatest promise is cardiac computed tomography (CT).

When the first CT scanners were introduced into clinical practice in the 1970s, cardiac imaging was not feasible, as the time required to acquire an image—approximately five minutes—ruled out a motionfree image of the heart and coronary vessels.

Over the ensuing decades, CT technology has improved dramatically. High spatial and temporal resolution—which are required for clinically useful cardiac imaging—have been achieved with the introduction of multiple rows of detectors (from 4 to 16 and, most recently, 64), faster gantry rotation, and sophisticated ECG cardiac-gating techniques.

Massachusetts General Hospital recently became the first hospital in New England to acquire and begin using a 64-slice, multi-detector CT (MDCT) scanner, which is used exclusively for the evaluation of cardiac patients. This state-of-the-art technology virtually freezes the heart’s detail and clarity. This is achieved in a single breathhold with a scan time of just 8-12 seconds, a radiation exposure equivalent to a chest CT scan, and a door-to-door time of approximately 15 minutes.

INDICATIONS
Presently, the indications for the use of Mass General’s 64-slice cardiac CT scanner are to:
• rule out significant CAD (e.g., as part of a routine pre-operative exam) in patients with low and regular heart rates
• rule out CAD in patients with atypical chest pain and an intermediate risk of CAD
• evaluate patients with inconclusive ECG stress tests
• visualize anomalous coronary arteries
• establish the patency of bypass grafts
• visualize the cardiac anatomy for congenital malformations, pulmonary venous return, and masses
• detect and quantify coronary plaque

EXCLUSION CRITERIA
• arrhythmias
• pregnancy
• impaired renal function
• allergy to the iodinated contrast agent
• myeloma

Although not yet established through clinical trials, it is anticipated that as a result of earlier diagnosis and treatment, cardiac CT will reduce morbidity and mortality among patients with suspected CAD.

A ROLE IN PATIENT MANAGEMENT
Current evidence suggests that cardiac CT may also have an important role in the management of patients with established CAD. It is the only non-invasive technique in widespread clinical use that can obtain information about the amount and composition of plaques in the coronary arteries, which are the cause of most acute coronary events. Thus, cardiac CT could become a valuable tool for evaluating patients who have had a mild myocardial infarction to determine whether they are candidates for aggressive treatment aimed at reducing their risk of a subsequent coronary event or sudden cardiac death.

Investigators in the Massachusetts General Hospital Department of Radiology and Division of Cardiology have been actively involved in cardiac CT research during the past five years, and have published numerous papers on their work (see Selected References). Research currently under way by this group is focused on a variety of new potential applications for cardiac CT. These include functional studies of myocardial perfusion and the role this technology may play in triaging ED patients with acute chest pain.

Undoubtedly the applications of cardiac CT will increase as investigators at Mass General and elsewhere continue to study its potential and as the technology continues to improve. But there is no question that this state-of-the-art technology is already having a major impact on patient care.

SELECTED REFERENCES
Hoffman U, Moselewski F, Cury R, Ferencik M, Jang I, Diaz L, Abbara S, Brady T, Achenbach S. Predictive value of 16-slice multi-detector spiral CT to detect significant obstructive coronary artery disease in patients at high risk for CAD: patient vs. segment-based analysis. Circulation 2004; 110:2638-2643.

Achenbach S, Moselewski F, Ropers D, Ferencik M, Hoffman U, MacNeill B, Pohle K, Baum U, Anders K, Jang I, Daniel W, Brady T. Detection of calcified and non-calcified coronary atherosclerotic plaque by contrast-enhanced, submillimeter multidetector spiral CT:
a segmentbased comparison to IVUS. Circulation 2004;109:14-17

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