Coronary artery calcium score improves cardiovascular risk prediction in persons without indication for statin therapy

BACKGROUND: Recent revision to the Canadian Cardiovascular Society (CCS) guidelines on cardiovascular disease (CVD) risk stratification provides expanded recommendations for statin therapy. If CVD risk in the remaining individuals can further be stratified and discriminated by additional risk assessment using coronary artery calcium (CAC) scoring is unknown.

METHODS AND RESULTS: In a retrospectively analyzed subgroup comprising 1934 participants from the Heinz Nixdorf Recall study, who did not meet criteria for statin therapy based on current CCS guidelines, traditional CVD risk variables and CAC were measured. Between 2000 and 2008, incident CVD events, i.e. coronary deaths, non-fatal myocardial infarction, coronary revascularization, stroke and CV death were determined. Those 43 participants who experienced 55 CVD events (5-year risk to first event: 2.2% (1.6-3.0%)) had higher CAC scores than those who did not (p<0.0001). In multiple Cox regression analysis including age, sex, total-/HDL-cholesterol ratio, and antihypertensive medication, log2(CAC+1) remained an independent predictor of CVD events (HR=1.21 (1.09-1.33), p<0.001). Measures of discrimination improved with the addition of CAC into the model: the incremental discrimination improvement was 0.0167, p=0.014. Net reclassification improvement using risk categories of 0-<3%, 3-10% and >10% was 25.1%, p=0.01, largely driven by a 32.6% correct up-classification in persons with events. Yet, only 38 (2%) of participants were identified being at high risk using CAC imaging in addition to traditional risk factor assessment.

CONCLUSION: Adding CAC to traditional risk assessment in persons without indication for statin therapy improves discrimination. However, reclassification to the high risk category and overall event rates seem too low to justify liberal CAC testing in all these individuals.