Coronary artery calcium scores and risk for cardiovascular events in women classified as "low risk" based on Framingham risk score: the multi-ethnic study of atherosclerosis (MESA).

Objective: To assess coronary artery calcium (CAC) score and subsequent risk for coronary heart disease (CHD) and cardiovascular (CVD) events among asymptomatic women judged to be at low risk by the Framingham risk score (FRS), a common approach for determining 10-year absolute risk for CHD. Based on population survey data, 95% of American women are considered at low risk based on FRS.

Methods: The Multi-Ethnic Study of Atherosclerosis (MESA) included 3601 women aged 45 to 84 years at baseline. The CAC score was measured by coronary computed tomography. Cox proportional hazard models were used to examine the CHD and CVD risk associated with CAC score among women classified as "low risk" based on FRS.

Results: Excluding women with diabetes and those older than 79 years, 90% of women in MESA (mean +/- SD age, 60 +/- 9 years) were classified as "low risk" based on FRS. The prevalence of CAC (CAC score > 0) in this low-risk subset was 32% (n = 870). Compared with women with no detectable CAC, low-risk women with a CAC score greater than 0 were at increased risk for CHD (hazard ratio, 6.5; 95% confidence interval, 2.6-16.4) and CVD events (hazard ratio, 5.2; 95% confidence interval, 2.5-10.8). In addition, advanced CAC (CAC score > or = 300) was highly predictive of future CHD and CVD events compared with women with nondetectable CAC and identified a group of low-risk women with a 6.7% and 8.6% absolute CHD and CVD risk, respectively, over a 3.75-year period.

Conclusions: The presence of CAC in women considered to be at low risk based on FRS was predictive of future CHD and CVD events. Advanced CAC identified a subset of low-risk women at higher risk based on current risk stratification strategies.