Incorporating the number of coronary arteries with calcified plaque adds predictive value to the Agatston coronary artery calcium (CAC) score for coronary heart disease (CHD) and cardiovascular disease (CVD) events, according to data published in JACC: Cardiovascular Imaging.
“While elegant and simple, the Agatston score and other current CAC scoring algorithms do not account for the distribution of CAC within the coronary tree,” the study authors explained. “Therefore 2 patients with the same CAC score may have significantly different patterns of CAC involvement.”
Researchers evaluated 3262 patients (mean age: 66 ± 10 years; 42% women) from the MESA (Multi-Ethnic Study of Atherosclerosis) study who had baseline CACs >0 for a median follow-up period of 10 years. Within that time frame, there were 368 CHD and 493 CVD events.
Multi-vessel CAC was defined by the number of coronary vessels with CAC (scored 1-4) and the “diffusivity index” (1 – CAC in most affected vessel/total CAC) and was implemented to categorize patients by concentrated and diffuse CAC patterns.
Among all patients, the mean CAC score was 291 ± 555 Agatston Units and mean number of vessels with CAC was 2.2 ± 1.0. The percentage of CAC in the most affected vessel was 24% ± 15% for 2-vessel CAC, 38% ± 15% for 3-vessel CAC, and 46% ± 13% for 4-vessel CAC.
Adding the number of vessels with CAC helped better predict the number of CHD and CVD events in survival analysis (hazard ratio [HR]: 1.9-3.5 for 4-vessel vs 1-vessel CAC), area under the curve (AUC) analysis (C-statistic improvement of 0.01-0.033), and net reclassification improvement (NRI) analysis (category-less NRI 0.10-0.45).
While diffuse CAC patterns were associated with worse outcomes for patients with ≥2 vessels with CAC (HR: 1.33-1.41; P<.05), it is important to note that adding this variable to the traditional CAC score and number of vessels with CAC did not further improve global risk prediction.
Myocardial infarctions (n=154), resuscitated cardiac arrests (n=19), CHD deaths (n=65), revascularizations with angina (n=130), strokes (n=89), and other CV/other atherosclerotic deaths made up the total CHD and CVD events during follow-up. The authors noted that the event rates increased with more number of vessels with CAC. “Within subpopulations defined by the number of vessels with CAC, event rates were lowest in those with a concentrated CAC pattern, and progressively higher with an intermediate and diffuse pattern,” they stated.
There was a 2.5 to 3.5 fold increase in CHD risk and 2.0 to 2.5 fold increase in CVD risk with 4-vessel CAC compared with 1-vessel CAC in models adjusted for age, gender, and race, which adjusted for CAC as a categorical, continuous, and log-transformed variable (all P<.05).
Important to note, however, that improvement in risk stratification by adding the number of vessels was only seen in the intermediate CAC score range (1-300).
“The most important finding is that simple addition of the number of vessels with CAC to the traditional Agatston scores improves both AUC and the NRI for prediction of CHD and CVD events,” the authors wrote.
Perhaps most helpful to the clinician is that this addition does not require a re-measurement or a complicated calculation and it is available on all CAC scores that report on a per-vessel basis.
“While we await development of a new comprehensive CAC scoring algorithm,” researchers added, “clinicians may consider reporting and interpreting the number of vessels with CAC in addition to a total CAC burden score on routine ungated and gated non-contrast chest and cardiac CT scans, particularly when CAC burden is intermediate.”
Blaha MJ, Budoff MJ, Tota-Maharaj R, et al. Improving the coronary artery calcium score – addition of regional measures of calcium distribution: Multi-Ethnic Study of Atherosclerosis (MESA). JACC Cardiovasc Imaging. 2016. doi:10.1016/j.jcmg.2016.03.001.