Background The microanatomic features of the atherosclerotic plaque at risk of disruption include a large lipid core, a high macrophage content, and a thin cap. The relation between lipid core size, plaque size, and cap thickness either with each other or with the degree of stenosis has yet to be evaluated in human coronary arteries.

Methods and Results Atherosclerotic coronary plaques (n=160) were obtained from 31 subjects who died suddenly of ischemic heart disease. In coronary arteries perfused with formol saline at a pressure of 100 mm Hg, stenosis was measured by comparison of the minimal lumen size at the site of a plaque with that of the lumen in an adjacent normal segment of artery. Plaque size, the size of the lipid core, and the thickness of the cap were measured in histological sections. Lipid core size ranged from 0% to 82% of overall plaque size. Seventeen percent of plaques had a core size of >50%. Linear regression showed no relation of core size to stenosis (r=.21). Absolute plaque size bore no relation to core size (r=.14). Minimal cap thickness was not related to core size (r=.06). Ten percent of plaques predicted to be angiographically invisible had cores of >50%.

Conclusions Two major determinants of plaque vulnerability, core size and cap thickness, are not statistically related. Neither of these two factors that confer vulnerability are related to absolute plaque size or to the degree of stenosis.