Why is Atherosclerotic Cardiovascular Disease Risk Overestimated by the ACC/AHA Pooled Cohort Equation?

The 2013 ACC/AHA Cholesterol Guidelines expand the recommendations for statin use to populations previously felt to be at lower risk. Central to risk-estimation in these guidelines is a new equation for determination of atherosclerotic cardiovascular disease (ASCVD) risk. However, this risk model has been criticized overestimating ASCVD risk in validation studies of the model. Using the Women's Health Study, Cook et al. sought to determine the reasons for risk-overestimation by the ACC/AHA model. Among 27,542 women, 632 experienced an ASCVD event, defined as any myocardial infarction, any stroke, or death from a cardiovascular cause. The average 10-year predicted risk was 3.6% in comparison to an observed risk of 2.2%. When stratified by risk, the ratio between predicted to actual rates was greater for lower risk groups (less than 7.5% risk; ratio 1.90 or higher) than higher risk groups (greater than or equal to 7.5% risk; ratio over 1.4). Statin use and revascularization rates increased over the period of the cohort study, particularly among …