The denser coronary artery plaque is, the lower the risk may be of coronary heart disease (CHD) and cardiovascular disease (CVD), according to a study published in the Jan. 15 issue of JAMA. This finding suggests that the current method of predicting risk, the Agatson coronary artery calcium (CAC) score, may need to be re-evaluated.

“Current scoring systems assume that denser heart plaque (CAC) is more hazardous, but we found the opposite," lead author Michael H. Criqui, MD, MPH, of the University of California, San Diego, in La Jolla, said in a press release.

The investigators used data from the Multi-Ethnic Study of Atherosclerosis (MESA), a study of adults aged 45 to 84 from four different ethnic groups with no history of known CVD from six communities across the U.S. They determined a CAC density score for each of the 3,398 participants. Each had a baseline CT scan that found a CAC score greater than zero. As outcomes, they determined the incidence of CHD and all CVD events.

Patients were followed up for an average of 7.6 years. There were a total of 175 CHD events. CAC volume was independently associated with CHD (hazard ratio [HR] 1.81 per standard deviation [SD] increase) absolute risk increase of 6.1 per 1,000 person-years. For CVD the HR was 1.68 per SD increase, absolute risk increase of 7.9 per 1,000 person-years.

CAC density scores were independent and inverse, with an HR of 0.73 per SD increase for CHD, a decrease in absolute risk of 5.5 per 1,000 person-years and an HR of 0.71 per SD increase for CVD, a decrease in absolute risk of 8.2 per 1,000 person-years.

The authors noted that one of the study’s limitations was the assessment of CAC density, which they called “crude.” Despite this limitation, they argued that their findings suggest the importance of considering CAC density.

In addition to CAC volume, they argued, “[t]he role of CAC density should be considered when evaluating current CAC scoring systems.”