CAC Score and Regional Measures of Calcium Distribution
Can regional measures of calcium distribution improve coronary artery calcium (CAC) scoring?
Data from MESA (Multi-Ethnic Study of Atherosclerosis) were used for the present analysis. Adults with a baseline Agatston CAC score >0 were included. Multivessel CAC was defined by the number of coronary vessels with CAC (scored 1-4, including the left main). The “diffusivity index” was calculated as 1 – (CAC in most affected vessel/total CAC), and was used to group participants into concentrated and diffuse CAC patterns. Area under the curve (AUC) and net reclassification improvement (NRI) analyses were performed for the primary outcomes of coronary heart disease (CHD) and cardiovascular disease (CVD).
A total of 3,262 adults (mean age 66 ± 10 years, 42% women) were included in the present analysis. During a median follow-up of 10.0 (9.5-10.7) years, 368 CHD and 493 CVD events occurred. The number of arteries with CAC was associated with increased CVD risk factors and increased risk of severity. The mean CAC score of the population was 291 ± 555 Agatston units, with a median and interquartile range of 86 (22–294). The mean number of vessels with CAC was 2.2 ± 1.0. The mean diffusivity index (% of CAC in the most affected vessel) was 24% ± 15 for two-vessel CAC, 38% ± 15 for three-vessel CAC, and 46% ± 13 for four-vessel CAC. Addition of information on the number of vessels with CAC significantly improved prediction of both CHD and CVD events (hazard ratio [HR], 1.9-3.5 for four-vessel vs. one-vessel CAC), AUC analysis (C-statistic improvement of 0.01-0.033), and NRI analysis (category-less NRI 0.10-0.45). While a diffuse CAC pattern was associated with worse outcomes in participants with ≥2 vessels with CAC (HR, 1.33-1.41; p < 0.05), adding this variable to the Agatston CAC score and number of vessels with CAC did not further improve global risk prediction.
The investigators concluded that the number of coronary arteries, consistent with diffuse disease, added to risk prediction for CHD and CVD events.
These data suggest that examining the number of coronary arteries in which CAC is present, together with the CAC score, is helpful in estimating risk of future events, but not for those with scores over 300. Thus, this information is most helpful in those with intermediate CAC scores.
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