Location, distribution of calcium may improve coronary artery calcium scoring for cardiovascular events

Determining the number of coronary arteries with calcified plaque adds significantly to the traditional Agatston coronary artery calcium (CAC) score for the prediction of cardiovascular events, particularly when traditional scores are in the intermediate range (1 to 300), a study found.

Because Agatston CAC scoring does not include information on the location and distributional pattern of calcified plaque, researchers sought to determine whether including such measures might add to the traditional score by improving its ability to predict cardiovascular events.

Researchers studied 3,262 individuals with a baseline CAC >0 from the Multi-Ethnic Study of Atherosclerosis (MESA). Multivessel CAC was defined by the number of coronary vessels with CAC (scored 1 to 4, including the left main). In participants with CAC in ≥2 vessels, researchers calculated a diffusivity index representing the degree of dispersion of CAC within the coronary tree. A higher diffusivity index represented a more diffuse pattern of CAC, while a smaller diffusivity index represented a great percentage of the total CAC in a single artery. The diffusivity index was calculated as 1−(CAC in most affected vessel/total CAC).

Mean age of the population was 66±10 years, with 42% women. Median follow-up was 10.0 years, and there were 368 coronary heart disease (CHD) and 493 cardiovascular disease (CVD) events during follow-up. Results appeared in the April JACC: Cardiovascular Imaging.

Considerable heterogeneity existed between CAC score group and number of vessels with CAC (P<0.01), the authors wrote. Adding the number of vessels with CAC significantly improved prediction of CHD and CVD events in survival analysis, area under the curve analysis, and net reclassification improvement analysis.

The researchers noted that while a diffuse CAC pattern was associated with worse outcomes in participants with ≥2 vessels with CAC (HR, 1.33 to 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.

“This simple measure of multi-vessel CAC does not require re-measurement or a complicated calculation, and is available on all CAC scores that report CAC on a per-vessel basis,” the authors wrote. “Our results therefore point to a parsimonious method for improving CAC scoring, and have direct implications for clinical risk prediction and for future development of improved CAC scoring.”