I the past decade, treatment of patients with coronary artery disease has increasingly focused on altering the properties of the atherosclerotic plaque. Until recently, there has been no noninvasive method to detect the presence of coronary artery plaque in the absence of flow-limiting stenoses. The development of a new generation of computed tomography (CT) scanners capable of detecting small amounts of coronary calcium represents an important advance in the noninvasive identification of higher risk patients with nonobstructive atherosclerosis. Patients with excessive coronary calcium based on ageand genderspecific reference values are at higher risk for obstructive and nonobstructive coronary disease, and probably for coronary events as well.1–6 Although most experts agree that asymptomatic patients with excessive coronary calcium should receive intensified preventative care, there are few data upon which to make treatment recommendations. Although there is controversy as to which patients should undergo this screening test, the emergence of for-profit imaging centers and direct-to-consumer advertising has led to significant numbers of self-referred patients with abnormal test results seeking treatment advice. Unfortunately, many existing treatment algorithms based on calcium score include recommendations for unproven therapies such as antioxidant vitamins and recommendations for expensive testing including stress testing, angiography, and coronary revascularization. The Dallas Heart Disease Prevention Project is a large cross-sectional epidemiologic study designed to study the gene-environment interactions causing cardiovascular disease in the ethnic populations of Dallas County. As part of this study, approximately 3,000 randomly selected Dallas County residents aged 30 to 60 years will undergo electron beam CT (EBCT). Although 1 goal of this study is to better understand how to interpret EBCT results, the study ethics committee mandated that participants be informed of test results and their physicians be provided guidelines for interpretation. Until clinical trial data become available, there are no “evidence-based” guidelines for the prevention of cardiovascular events based on EBCT results, particularly in the case of asymptomatic patients. Thus, as part of this project, we have developed guidelines that incorporate the calcium score with current National Cholesterol Education Panel (NCEP) guidelines. There are 2 accepted modalities for detection of coronary calcium, EBCT and helical CT. EBCT has slightly shorter image acquisition time, but there have been no definitive studies comparing the 2 modalities to determine which is superior for the detection of coronary calcium. With use of EBCT during a single breath-hold, the patient’s heart is imaged in 3-mm cross-sectional slices. The resolution of the scan allows identification of coronary arteries, and the coronary calcium is readily visible in contrast to the soft tissues of the heart. Several commercially available software analysis packages allow easy identification of calcium deposits and calculation of calcium deposit area. The area of the calcified plaque is then multiplied by a coefficient based on peak x-ray density yielding a plaque-specific calcium score. The total calcium score is the sum of the scores for each individual plaque. The degree of calcium of the coronary arteries correlates directly with the degree of coronary athersclerosis when the total calcium score is related to the total amount of plaque in the coronary tree.1,4,7–9 However, areas of calcium on EBCT do not necessarily represent significant coronary stenoses. Most of the data relating calcium scores with presence and degree of atherosclerosis come from studies of symptomatic populations. Generalizing these results to an asymptomatic population may not be appropriate because of differences in disease prevalence. However, in asymptomatic subjects the reported sensitivity of EBCT in detecting obstructive coronary approaches 90%, and the average reported specificity is 55%.1 Particularly in younger adults (,40 years), significant atherosclerosis can be present without any detectable calcium by EBCT.1,10 Although the sensitivity of the test increases with age, the specificity of the test decreases with age because calcification occurs gradually in an age-independent process. Women develop calcium on average at later ages than men, and median calcium scores for women are similar to median scores of men aged #10 years.10 Because coronary calcium increases with age and From the Department of Internal Medicine, Division of Cardiology, The University of Texas Southwestern Medical School, Dallas, Texas. The report was supported by grants from the Donald W. Reynolds Foundation, Las Vegas, Nevada; and the American Heart Association Texas Affiliate, Austin, Texas. Manuscript received October 30, 2000; revised manuscript received and accepted January 22, 2001. Address for reprints: Thomas C. Andrews, MD, Consultants in Cardiology, 1300 West Terrell Avenue, Suite 500, Fort Worth, Texas 76104. E-mail: tandrews@hcin.net.
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Mar 1, 2008
William R Davis + 1
Open Access
