Validation of the Atherosclerotic Cardiovascular Disease Pooled Cohort Risk Equations
What is the calibration and discrimination of the American College of Cardiology (ACC)/American Heart Association (AHA) Pooled Cohort risk equations in a contemporary US population?
This study population included adults ages 45-79 years enrolled in the REGARDS (Reasons for Geographic and Racial Differences in Stroke) study between January 2003 and October 2007, and followed up through December 2010. The investigators studied participants for whom atherosclerotic cardiovascular disease (CVD) risk may trigger a discussion of statin initiation (those without clinical atherosclerotic CVD or diabetes, low-density lipoprotein cholesterol (LDL-C) level between 70 and 189 mg/dl, and not taking statins; n = 10,997). The main outcome measure was predicted risk and observed adjudicated atherosclerotic CVD incidence (nonfatal myocardial infarction, coronary heart disease [CHD] death, nonfatal or fatal stroke) at 5 years because REGARDS participants had not been followed up for 10 years. Additional analyses, limited to Medicare beneficiaries (n = 3,333), added atherosclerotic CVD events identified in Medicare claims data.
There were 338 adjudicated events (192 CHD events, 146 strokes). The observed and predicted 5-year atherosclerotic CVD incidence per 1,000 person-years for participants with a 10-year predicted atherosclerotic CVD risk of <5% was 1.9 (95% confidence interval [CI], 1.3-2.7) and 1.9, respectively, risk of 5% to <7.5% was 4.8 (95% CI, 3.4-6.7) and 4.8, risk of 7.5% to <10% was 6.1 (95% CI, 4.4-8.6) and 6.9, and risk of ≥10% was 12.0 (95% CI, 10.6-13.6) and 15.1 (Hosmer-Lemeshow χ2 = 19.9, p = 0.01). The C index was 0.72 (95% CI, 0.70-0.75). There were 234 atherosclerotic CVD events (120 CHD events, 114 strokes) among Medicare-linked participants, and the observed and predicted 5-year atherosclerotic CVD incidence per 1,000 person-years for participants with a predicted risk of <7.5% was 5.3 (95% CI, 2.8-10.1) and 4.0, respectively, risk of 7.5% to <10% was 7.9 (95% CI, 4.6-13.5) and 6.4, and risk of ≥10% was 17.4 (95% CI, 15.3-19.8) and 16.4 (Hosmer-Lemeshow χ2 = 5.4, p = 0.71). The C index was 0.67 (95% CI, 0.64-0.71).
The authors concluded that in this cohort of US adults, observed and predicted 5-year atherosclerotic CVD risks were similar, indicating that these risk equations were well calibrated in the population for which they were designed to be used, and demonstrated moderate to good discrimination.
In this large, contemporary, population-based cohort of US adults, the recently published ACC/AHA Pooled Cohort risk equations appeared to overestimate atherosclerotic CVD risk. However, differences in the observed and predicted atherosclerotic CVD risk were small when limited to participants without diabetes, with an LDL-C level between 70 and 189 mg/dl, and who were not already taking statins. Calibration in this group is particularly important because it represents the primary population for whom high predicted risk is intended to trigger a discussion about statin initiation. Furthermore, the observed and predicted atherosclerotic CVD risks were much more similar when evaluated in participants with Medicare insurance coverage, including the atherosclerotic CVD events identified in Medicare claims. In addition to demonstrating good calibration, the Pooled Cohort risk equations had good discrimination. These findings would support the validity of the Pooled Cohort risk equations to inform clinical management decisions.
Keywords: Cholesterol, Stroke, Atherosclerosis, Cholesterol, LDL, Hydroxymethylglutaryl-CoA Reductase Inhibitors, Cardiovascular Diseases, ACC Annual Scientific Session
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