American College of Cardiology/American Heart Association expert consensusdocument on electron-beam computed tomography for the diagnosis and prognosis of coronary artery disease

Coronary artery calcification is part of the development of atherosclerosis ; it occurs exclusively in atherosclerotic arteries and is absent in the no rmal vessel wall. Electron-beam computed tomography (EBCT), the focus of th is document, is a highly sensitive technique for detecting coronary artery calcium and is being used with increasing frequency for the screening of as ymptomatic people to assess those at high risk for developing coronary hear t disease (CHD) and cardiac events, as well as for the diagnosis of obstruc tive 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 calc ium score has been advocated by some as a potential surrogate for age in ri sk-assessment models. EBCT has also been proposed as a useful technique for assessing the progres sion or regression of coronary artery stenosis in response to treatment of risk factors such as hypercholesterolemia. EBCT uses an electron beam in st ationary 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 breathholding sequences. Current EBCT soft ware permits quantification of calcium area and density. Histological studi es 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 correl ated 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 19 99 and also used information obtained when possible from at-tides in press and data sets from EBCT research centers. We also reviewed the Blue Cross/B lue Shield (BC/BS) Technology Evaluation Center (TEC) assessment of EBCT fo r screening asymptomatic patients for CAD and for diagnosing CHD in symptom atic patients. Three members of this Writing Group attended the recent AI-I A Prevention V Conference on "Identification of the High-Risk Patient for P rimary Prevention," and one of our members is also a participant in the des ign of the National Institutes of Health/National Heart, Lung, and Blood In stitute (NIH/NHLBI) forthcoming Multiethnic Study of Atherosclerosis (MESA) , which will include a prospective assessment of EBCT in asymptomatic peopl e. We performed meta-analysis on the relationship between CHD and calcium prev alence in patients undergoing EBCT and cardiac catheterization to determine the diagnostic accuracy of EBCT in catheterized patients. We also performe d a meta-analysis of published data in order to compare the diagnostic char acteristics of the available alternative tests for detecting angiographic o bstructive CAD. The studies demonstrate a high sensitivity of EBCT for CAD, a much lower specificity, and an overall predictive accuracy of approximat e to 70% in typical CAD patient populations. The test has proven to have a predictive accuracy approximately equivalent to alternative methods for dia gnosing CAD but has not been found to be superior to alternative noninvasiv e methods leg, SPECT [single photon emission computed tomography] imaging). The majority of the members of the Writing Group, would not recommend EBCT for diagnosing obstructive CAD because of its low specificity thigh percen tage of false-positive results), which can result in additional expensive a nd unnecessary testing to rule out a diagnosis of CAD. The 1999 ACC/AHA Cor onary Angiography Guideline Committee reached a similar conclusion (1). Because the severity of coronary atherosclerosis is known to be associated with risk of coronary events, coronary calcium scores should likewise corre late with risk for coronary events. However, for a test to be most valuable when asymptomatic patients are screened, it should increase the likelihood of CHD above the probability determined by standard and readily available assessments, such as the Framingham risk model based on levels of blood pre ssure, cholesterol, high-density lipoprotein (HDL) cholesterol, cigarette s moking, plasma glucose, and age. The published literature does not complete ly answer the question of whether the EBCT calcium score is additive to the Framingham score for defining CHD risk in asymptomatic patients. In one re cent large study (2), the addition of EBCT data provided no incremental val ue to the risk determined by the Framingham and National Cholesterol Educat ion Program risk factors in a direct comparison. There have been other stud ies that examine this point (2-4), but those reports did not adequately tes t whether EBCT scores were incremental to the other risk factor data. This is an area of important current investigation, including the NIH/NHLBI's ME SA study. It is possible that a positive calcium score might be valuable in determining whether a patient who appears to be at intermediate CHD risk i s actually at high risk. Conversely, a low or absent EBCT calcium score may also prove useful in determining a low likelihood of developing CHD. This may be particularly beneficial in elderly asymptomatic patients in whom the management of other risk factors may be modified according to the calcium score. Selected use of coronary calcium scores when a physician is faced wi th the patient with intermediate coronary disease risk may be appropriate. However, the published literature does not clearly define which asymptomati c people require or will benefit from EBCT. Additional appropriately design ed studies of EBCT for this purpose are strongly encouraged. In the setting of this degree of uncertainty, EBCT screening should not be made available to the general public without a physician's request. The usefulness of EBCT in determination of changing calcium scores that cor relate with regression or progression of CHD is currently being studied int ensively. However, the test-to-test variability and the interrater reliabil ity of the calcium score measurement in the same individual studied at clos e intervals in time have been deterrents to the recommendation of serial EB CT scans for determining the response of coronary artery stenosis lesions t o medical interventions designed to cause regression of disease. The Writin g Group concluded that this is a promising use of EBCT, but the small numbe r of published studies require corroboration before EBCT can be widely reco mmended for this purpose. Our conclusions are consistent with the recommendation of the Agency for He alth Care Policy and Research-funded BC/BS TEC, the Prevention V Conference report of the AHA (Dr Philip Greenland), and the MESA project currently be ing planned by the NIH/NHLBI. The latter study will evaluate EBCT and other techniques in the long-term assessment of CHD risk in 6500 apparently heal thy people. As additional data are obtained, our conclusion might require r evision. This Writing Group encourages further properly designed outcomes research u sing EBCT and additional studies of the role of EBCT and patient follow-up for assessing progression or regression of CHD.