SAN DIEGO, CA — Coronary artery calcium (CAC) density scores may be useful to more accurately predict cardiovascular disease risk in patients deemed to be at intermediate risk based on Framingham risk scores, a new study suggests. However, the improvement in risk prediction was modest, and the findings do not imply that lower-risk individuals should undergo CAC testing, an accompanying editorial cautions.
The observational study, based on a median of 7.6 years of follow-up of participants in the Multi-Ethnic Study of Atherosclerosis (MESA), was presented at last week's American Heart Association 2013 Scientific Sessions and simultaneously published online November 18, 2013 in the Journal of the American Medical Association.
A total of 13.9% of patients who were first classified as being at intermediate risk of CVD events were reclassified as being at low or high risk, based on their CAC-density scores. Therefore, "the role of CAC density should be considered when evaluating current CAC scoring systems," the authors, led by Dr Michael H Criqui (University of California, San Diego), conclude.
However, importantly, the authors "do not recommend widespread CAC testing based on this improved risk-assessment method," Dr Philip Greenland (Northwestern University, Chicago, IL), points out in an accompanying editorial. "Although CAC-density scoring can be useful for increasing the discrimination of CAC testing at little or no cost, the evidence on CAC testing in general is not sufficient to justify wider testing based on these relatively modest findings," he writes.
What Does Calcium Density Tell Us?
CAC scores determined by computed-tomography (CT) scans are strong predictors of whether an individual will have CVD, and increasing evidence suggests that greater calcium density in plaques might be protective for this outcome, the authors write.
More than half of middle-aged adults in the US have CAC, and by age 70, more than 90% have CAC.
The researchers hypothesized that, among the participants in the MESA trial, who came from six geographically diverse areas of the US, at any given volume of plaque burden, patients who had greater CAC-density scores would have a lower risk of incident CVD events.
They obtained data from 3394 individuals who participated in MESA and had CAC scores above 0 at baseline in 2000–2002. The participants were of multiple ethnicities, 45 to 84 years old, and free of known CVD at baseline.
During follow-up, there were 175 coronary heart disease events (MI, resuscitated cardiac arrest, or death from CHD) and 90 other CVD events (stroke or death from stroke).
As the researchers had hypothesized, at any CAC-volume score, increases in CAC-density scores were linked with a significantly lower risk of CHD and CVD.
"The data presented here—that CAC density was inversely related to CVD events at a given CAC volume and that CAC volume was more predictive when adjusted for CAC density—are novel observations," Criqui and colleagues write. Measurements of CAC and CAC density appear to be particularly useful in correctly classifying risk in individuals who appear to have an intermediate risk of CVD, they add.
CAC Testing Remains "Reasonable" for Intermediate-Risk Patients
According to recent American Heart Association/American College of Cardiology guidelines, measurement of CAC is considered "reasonable" to assess CVD risk in asymptomatic patients deemed to be at intermediate risk—that is, patients who have a 10% to 20% risk of a CVD event in the next 10 years—Greenland writes.
"A normal (ie, zero) CAC score in such a patient could be sufficiently reassuring to avoid drug treatments, whereas an elevated CAC score could encourage the use of long-term statins and aspirin," he notes.
The study by Criqui and colleagues showed that CAC-density readings could improve the classification of patients deemed to be at intermediate risk of CVD. However, even with the added value of CAC-density scores, it is too early to justify wider use of CAC testing in lower-risk patients, according to Greenland. Further study examining cost and effectiveness of CAC screening is needed to help guide clinical practice and policy decisions.
Criqui reports receipt of a grant to his institution from the National Institutes of Health/National Heart, Lung, and Blood Institute (NIH/NHLBI). Disclosures for the coauthors are listed in the paper. Greenland reports receipt of a grant from the NIH/NHLBI.
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