Coronary Calcium as an Indicator of Coronary Artery Disease

Abstract

Due to biological factors (mainly arterial remodeling) and the methodological limitations of a contour method, coronary angiography may underestimate both the extent and the severity of atherosclerosis (TopoL and Nissen 1995). But, angiography remains the clinical standard method for defining coronary anatomy in patients. Angiography and electron beam computed tomography (EBCT) evaluate two facets of atherosclerotic plaque disease, that is, luminal narrowing and calcified plaque itself. This was emphasized by a recent study in 49 patients with normal or near-normal angiograms, of whom 28 (57%) had quantifiable coronary calcium (Schmermund et al. 1998b). Coronary calcium in these patients was usually observed in the form of “spotty” calcium as defined by Kajinami et al. (1997). Some coronary segments with spotty calcium showed an increased lumen caliber, probably due to exaggerated compensatory remodeling. Accordingly, atherosclerotic plaque formation in these patients did not entail luminal narrowing, but rather even resulted in a seemingly paradoxical increased lumen in some cases. While other noninvasive tests focus on the physiological consequences of coronary obstruction, EBCT represents anatomic disease itself (Fig. 4.5.1) (ERBEL 1996). Indeed, early stages of atherosclerotic plaque formation that may oftentimes go undetected by angiography are reliably visualized by EBCT (Schmermund et al. 1998b; Baumgart et al. 1997).