Coronary Calcification by Electron Beam Tomography: Comparison with Coronary Risk Factors and Angiography

The development and progression of coronary artery disease is the result of exposure to a variety of different risk factors. In larger populations, strong associations exist between risk factors and the development of both angiographic and clinical coronary artery disease. But, this relationship is extremely variable in individual subjects. Coronary calcification is a specific marker of coronary artery disease. Its formation and progression is determined by largely identical risk factors compared with angiographic coronary artery disease. Coronary calcification quantitated by electron beam tomography (EBT) thus enables the non-invasive assessment of whether the risk factor exposure has actually led to the development of coronary atherosclerosis in an individual subject. Whereas other non-invasive tests focus on the physiological consequences of coronary obstruction, EBT represents anatomic disease itself. Because the propensity of plaques to cause coronary obstruction partly depends on the degree of arterial remodelling, large plaques may not necessarily appear as high-grade stenoses angiographically. Indeed, angiography and EBT evaluate two facets of atherosclerotic plaque disease, i.e. luminal obstruction and calcified plaque itself. Coronary calcification is strongly associated with the presence, extent, and severity of angiographic coronary artery disease. A number of studies have shown that it is clearly superior in this respect compared with conventional risk factors. However, because of the indirect relationships between plaque formation and luminal obstruction, EBT does not permit the site-specific prediction of coronary stenoses. Recent investigations have focused on the ability of EBT to represent the extent of anatomic coronary artery disease, which is an important predictor of future cardiac events. The availability of a simple, non-invasive test for the direct visualization of coronary artery disease holds great promise regarding improved definitions of the relationships between risk factors and coronary atherosclerosis as well as regarding the diagnosis of non-obstructive coronary disease, which can nevertheless result in acute events.