Background:
Prior studies suggest that African Americans (AA) have lower prevalence of coronary artery calcium (CAC) compared to whites, yet CAC has similar ability to predict coronary heart disease (CHD) events. The role of CAC as a screening tool for CHD risk in AA is unclear. We compared the diagnostic accuracy for CHD prevalence using the CAC score and the Framingham Risk Score (FRS) in an adult population of AA.
Methods:
CAC was measured in 2944 participants in the Jackson Heart Study, an NHLBI funded study of AA based in Jackson, MS. Approximately 8% of this cohort had known cardiovascular disease (CVD) defined as prior MI, angina, stroke, PTCA, CABG or PVD. Logistic regression, ROC and net reclassification index (NRI) analysis were used adjusting for age, gender, SBP, total and HDL cholesterol, smoking status, DM and BMI. FRS was calculated and those with DM were classified as high risk.
Results:
The mean age was 60, 65% were females, 26% had DM, 50% were obese and 30% were current or former smokers. Prevalent CVD was associated with older age, higher SBP, lower HDL and total cholesterol, and higher CAC. CAC was independently associated with prevalent CVD in our multivariable model [OR (95% CI): 1.26 (1.17, 1.35), p< 0.0001]. In ROC analysis, CAC improved the diagnostic accuracy (c statistic) of the FRS from 0.617 to 0.757 (p < 0.0001) for prevalent CVD. The FRS classified 30% of the cohort as high risk, 38.5% as intermediate risk and 31.5% as low risk. FRS classfied 51% of subjects with prevalent CVD as high risk. Addition of CAC to FRS resulted in net reclassification improvement of 4% for subjects with known CVD and 28.5% in those without CVD (see figure).
Conclusion:
In AA, the CAC is independently associated with prevalent CVD and improves the diagnostic accuracy of FRS for prevalent CVD by 14%. Addition of CAC improves the NRI of those with prevalent CVD by 4% and the NRI of individuals without CVD by 28.5%. Determination of CAC in AA may be useful in identifying individuals at risk of CVD and reclassifying individuals with low and intermediate FRS.
Diagnostic Value of Coronary Artery Calcium Score for Cardiovascular Disease in African Americans: The Jackson Heart Study
