Identification of patients at increased risk of first unheralded acute myocardial infarction by electron-beam computed tomography

Background-There is a clear relationship between absolute calcium scores (C S) and severity of coronary artery disease. However, hard coronary events h ave been shown to occur across all ranges of CS. Methods and Results-We conducted 2 analyses: in group A, 172 patients under went electron-beam CT (EBCT) imaging within 60 days of suffering an unheral ded myocardial infarction. In group B, 632 patients screened by EBCT were f ollowed up for a mean of 32 +/- 7 months for the development of acute myoca rdial infarction or cardiac death. The mean patient age and prevalence of c oronary calcification were similar in the 2 group; (53 +/- 8 versus 52 +/- 9 years and 96% each). In group B, the annualized event rate was 0.11% for subjects, with CS of 0, 2.1% for CS 1 to 99, 4.1% for CS 100 to 400, and 4. 8%: for CS > 400, and only 7%; of the patients had CS >400. However, mild, moderate, and extensive absolute CSs were distributed similarly between pat ients with events in both groups (34%, 35%, and 27%, respectively, in group A and 44%, 30%, and 22% in group B). In contrast, the majority of events: in both groups occurred in patients with CS >75th percentile (70% in each g roup). Conclusions-Coronary calcium is present in most patients who suffer acute c oronary events. Although the event rate is greater for patients with high a bsolute CSs, few patients have this degree of calcification on a screening EBCT. Conversely, the majority of events occur in individuals with high CS percentiles. Hence, CS percentiles constitute a more effective screening me thod to stratify individuals at risk.