During the past 2 decades, a number of innovative techniques have been introduced within diagnostic cardiology that have resulted in improved test performance (ie, sensitivity) for the detection of obstructive CAD. Improvements in test accuracy in the area of diagnostic cardiology have been uniformly associated with higher test costs. Historically, as new technology was developed, it was expected that users would pay for newer, more high-tech imaging tests without any justification of the incremental cost of the new technology. The resulting economic pressures placed on physicians in the current era of healthcare reform are forcing a rethinking of the medical applications of a number of testing modalities. The evaluation of CHD can utilize many testing modalities. The Writing Group accepted the principle that the future of any new technology must now undergo a rigorous evaluation before routine use and application in daily clinical decision making.

The limited diffusion of new technologies (eg, EBCT and contrast-enhanced echocardiography) in today’s healthcare market indicates that clinicians and healthcare administrators are making more cautious choices about new technology by awaiting a greater compendium of results applied throughout a wide variety of patient subsets. Although a new test may be less expensive than others previously available, in some cases, tests with low specificity may result in add-on tests that lead to additional costs without improving patient outcomes.

Coronary artery calcification is part of the development of atherosclerosis; it occurs exclusively in atherosclerotic arteries and is absent in the normal vessel wall. Electron-beam computed tomography (EBCT) is a highly sensitive technique for detecting coronary artery calcium and is being used with increasing frequency for the screening of asymptomatic people to assess those at high risk for developing coronary heart disease (CHD) and cardiac events, as well as for the diagnosis of obstructive coronary artery disease (CAD) in symptomatic patients.
The use of EBCT has the greatest potential for further determination of risk, particularly in elderly asymptomatic patients and others at intermediate risk. The calcium score has been advocated by some as a potential surrogate for age in risk-assessment models. EBCT has also been proposed as a useful technique for assessing the progression or regression of coronary artery stenosis in response to treatment of risk factors such as hypercholesterolemia.

^ Back to Top

EBCT uses an electron beam in stationary tungsten targets, which permits very rapid scanning times. Serial transaxial images are obtained in 100 ms with a thickness of 3 to 6 mm for purposes of detecting coronary artery calcium. Thirty to 40 adjacent axial scans are obtained during 1 to 2 breath-holding sequences. Current EBCT software permits quantification of calcium area and density. Histological studies support the association of tissue densities of 130 Hounsfield units (HU) with calcified plaque. However, a plaque vulnerable to fissure or erosion can be present in the absence of calcium. Also, sex differences play a role in the development of coronary calcium, the prevalence of calcium in women being half that of men until age 60 years.
EBCT calcium scores have correlated with pathological examination of the atherosclerotic plaque. This American College of Cardiology (ACC)/American Heart Association (AHA) Writing Group reviewed the literature on EBCT published between 1988 and 1999 and also used information obtained when possible from articles in press and data sets from EBCT research centers. We also reviewed the Blue Cross/Blue Shield (BC/BS) Technology Evaluation Center (TEC) assessment of EBCT for screening asymptomatic patients for CAD and for diagnosing CHD in symptomatic patients. Three members of this Writing Group attended the recent AHA Prevention V Conference on "Identification of the High-Risk Patient for Primary Prevention," and one of our members is also a participant in the design of the National Institutes of Health/National Heart, Lung, and Blood Institute (NIH/NHLBI) forthcoming Multiethnic Study of Atherosclerosis (MESA), which will include a prospective assessment of EBCT in asymptomatic people.

Source: American College of Cardiology/American Heart Association Expert Consensus Document on Electron-Beam Computed Tomography for the Diagnosis and Prognosis of Coronary Artery Disease