Aims: Little is known regarding the risk of atherosclerotic cardiovascular disease (ASCVD) conferred by changes in the volume and density of ascending thoracic aorta calcium (ATAC) over time. We evaluated changes in ATAC volume and density scores and incident ASCVD events.
Methods and results: The Multi-Ethnic Study of Atherosclerosis is a prospective cohort study of individuals without baseline clinical ASCVD. Ascending thoracic aorta calcium was measured from baseline and follow-up (mean interval 2.4 years) cardiac computed tomography (CT). Cox proportional hazard regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) per standard deviation for events after the follow-up exam adjusted for ASCVD risk factors, baseline ATAC and coronary artery calcium (CAC) volume and density, and changes in CAC volume and density. Among 5887 participants, 296 (5.0%) had detectable ATAC at baseline, follow-up, or both exams. A total of 403 events occurred over 9.5 years. An increase in ATAC volume was associated with coronary heart disease (CHD) (HR 1.90, 95% CI 1.14-3.16), ASCVD (HR 1.93, 95% CI 1.26-2.94), and ischaemic stroke (HR 2.14, CI 1.21-3.78). An increase in ATAC density was inversely associated with CHD (HR 0.29, 95% CI 0.14-0.60) and ASCVD (HR 0.42, 95% CI 0.23-0.76), but not stroke (HR 0.61, CI 0.23-1.61).
Conclusion: Ascending thoracic aorta calcium is uncommon on serial cardiac CT. However, changes in ATAC volume and density are both associated with incident ASCVD events, but in opposite directions. Serial assessments in those with baseline ATAC may provide insight into an individual's trajectory of ASCVD risk.