Use of coronary artery calcium testing to guide aspirin utilization for primary prevention: Estimates from the multi-ethnic study of atherosclerosis

Background-Aspirin for the primary prevention of coronary heart disease (CHD) is only recommended for individuals at high risk for CHD although the majority of CHD events occur in individuals who are at low to intermediate risk. Methods and Results-To estimate the potential of coronary artery calcium (CAC) scoring to guide aspirin use for primary prevention of CHD, we studied 4229 participants from the Multi-Ethnic Study of Atherosclerosis who were not on aspirin at baseline and were free of diabetes mellitus. Using data from median 7.6-year follow-up, 5-year number-needed-totreat estimations were calculated by applying an 18% relative CHD reduction to the observed event rates. This was contrasted to 5-year number-needed-to-harm estimations based on the risk of major bleeding reported in an aspirin metaanalysis. Results were stratified by a 10% 10-year CHD Framingham Risk Score (FRS). Individuals with CAC<100 had an estimated net benefit with aspirin regardless of their traditional risk status (estimated 5-year number needed to treat of 173 for individuals >10% FRS and 92 for individuals =10% FRS, estimated 5-year number needed to harm of 442 for a major bleed). Conversely, individuals with zero CAC had unfavorable estimations (estimated 5-year number needed to treat of 2036 for individuals >10% FRS and 808 for individuals =10% FRS, estimated 5-year number needed to harm of 442 for a major bleed). Sex-specific and age-stratified analyses showed similar results. Conclusions-For the primary prevention of CHD, Multi-Ethnic Study of Atherosclerosis participants with CAC=100 had favorable risk/benefit estimations for aspirin use while participants with zero CAC were estimated to receive net harm from aspirin.