ABSTRACT
BACKGROUND: Coronary artery calcium testing using noncontrast cardiac computed tomography is a guideline-indicated test to help refine eligibility for aspirin in primary prevention. However, access to cardiac computed tomography remains limited, with carotid ultrasound used much more often internationally. We sought to update the role of aspirin allocation in primary prevention as a function of subclinical carotid atherosclerosis. METHODS AND RESULTS: The study included 11 379 participants from the MESA (Multi-Ethnic Study of Atherosclerosis) and ARIC (Atherosclerosis Risk in Communities) studies. A harmonized carotid plaque score (range, 0-6) was derived using the number of anatomic sites with plaque from the left and right common, bifurcation, and internal carotid artery on ultrasound. The 5-year number needed to treat and number needed to harm as a function of the carotid plaque score were calculated by applying a 12% relative risk reduction in atherosclerotic cardiovascular disease (ASCVD) events and 42% relative increase in major bleeding events related to aspirin use, respectively. The mean age was 57 years, 57% were women, 23% were Black, and the median 10-year ASCVD risk was 12.8%. The 5-year incidence rates (per 1000 person-years) were 5.5 (4.9-6.2) for ASCVD and 1.8 (1.5-2.2) for major bleeding events. The overall 5-year number needed to treat with aspirin was 306 but was 2-fold lower for individuals with carotid plaque versus those without carotid plaque (212 versus 448). The 5-year number needed to treat was less than the 5-year number needed to harm when the carotid plaque score was ≥2 for individuals with ASCVD risk 5% to 20%, whereas the presence of any carotid plaque demarcated a favorable risk-benefit for individuals with ASCVD risk >20%. CONCLUSIONS: Quantification of subclinical carotid atherosclerosis can help improve the allocation of aspirin therapy.