Relation between the Framingham Risk Score, coronary calcium, and incident coronary heart disease among low-risk men

The Prospective Army Coronary Calcium Project is evaluating the predictive value of coronary artery calcium (CAC) in unselected, healthy, lower-risk, 40- to 50-year-old men. Although this study has found that coronary calcium is predictive of future coronary heart disease (CHD), criteria are needed to narrow the screening population to those in whom CAC measurement is most efficient (vs unselected screening of low-risk men). In 1,634 unselected volunteer men (mean age 42 years, mean 10-year CHD Framingham risk score [FRS] 4.6%, CAC prevalence 22.4%), we evaluated the independent relation between CAC and incident CHD over 5.6 years including hard events (hospitalized unstable angina, myocardial infarction, and CHD death) and coronary revascularization. The cohort was analyzed in tertiles of FRS for the relation between CAC and CHD outcomes. FRS tertile cutpoints were 0% to 3% (n = 547), >3% to 5% (n = 547), and >5% (n = 540) 10-year CHD risk. Over a mean follow-up of 5.6 +/- 1.5 years (range 1.0 to 8.3), there were 22 total CHD events, including 14 hard events and 8 revascularizations. Most events occurred in the highest FRS tertile (n = 14) versus the middle (n = 6) and lowest (n = 2) risk tertiles (p = 0.005). CAC and CHD events increased across FRS tertiles. Only in the highest FRS tertile was there a significant relation between CAC and CHD outcomes (hazard ratio 9.3). In conclusion, CAC screening could be of benefit in refining risk assessment of low-risk men, but only when the FRS exceeds approximately 5%.