LONDON – Coronary artery calcium as assessed by CT scan, widely considered the best marker of cardiovascular risk, just got significantly better.
The standard measure of coronary artery calcium (CAC) has been the Agatson score, which evaluates plaque calcium volume. But new evidence from the large, multicenter, prospective, observational Multi-Ethnic Study of Atherosclerosis (MESA) demonstrates that plaque calcium density is independently and inversely associated with both CHD and stroke risk. In other words, greater calcium density is protective against cardiovascular disease and counteracts the increased risk associated with greater calcium volume, Dr. Michael H. Criqui said at the annual congress of the European Society of Cardiology.
“We no longer believe in the Agatson score. We took a look at it and found out that at any given level of plaque calcium volume, a higher density score is protective. So when we look at our scans now, we no longer use the Agatson. We take the volume, then measure density separately, and we calculate a score that’s based on both,” explained Dr. Criqui, professor and chief of the division of preventive medicine at the University of California, San Diego.
Session moderator Dr. Sidney C. Smith Jr., was favorably impressed by the new analysis.
“Somehow we need to get this information in front of the guideline committees for the ESC, ACC [American College of Cardiology], and AHA [American Heart Association], because this is very interesting,” said Dr. Smith, professor of medicine at the University of North Carolina, Chapel Hill.
The MESA analysis included 3,398 adults followed for an average of 10.3 years. During that time 264 incident CHD events and 126 hard stroke events occurred.
“You find that as the calcium volume gets higher, the CHD risk gets much higher – up to fourfold higher for the fourth quartile. But we all knew that before. The new concept is that as your density score gets higher your risk goes way down. In the fourth quartile of density, you have only half the risk of developing a coronary event at any given calcium volume,” according to Dr. Criqui.
This confirms an earlier preliminary report by Dr. Criqui and coinvestigators based upon 7.6 years of MESA follow-up (JAMA. 2014 Jan 15;311:271-8). The number of cardiovascular events in the update is 47% greater than in the initial report, considerably strengthening the findings.
The predictive power of the combined CAC volume and density score was underscored by the finding that the area under the receiver operating curve for CHD events was 0.674. To put that in perspective, when the investigators applied the ACC/AHA risk calculator tool to the MESA data, the area under the receiver operating characteristic curve was less impressive at 0.654. Combining the risk prediction score and the CAC volume/density score further increases the predictive power, he noted.
Plaque calcium density was similarly predictive in men and women, in younger and older adults, and in all four ethnic groups participating in MESA: Hispanics, African Americans, non-Hispanic whites, and Asians.
For CHD, the hazard ratio was 1.83 for each standard deviation of CAC volume and 0.71 for each standard deviation of CAC density. For stroke, the impacts were slightly less: a hazard ratio of 1.46 for each standard deviation of CAC volume and 0.83 for each standard deviation of density.
Asked if any biomarkers are related to CAC density, Dr. Criqui replied, “Preliminary data show that most of the risk factors we know are bad for us, like diabetes and smoking, are associated with lower CAC density. And the things that are good for us, like exercise and statins, are associated with higher density.”
He and his coworkers are now looking at plaque calcium density versus volume in the abdominal and thoracic aorta to learn if the same relationships seen in the coronary arteries hold true.
MESA is funded by the National Heart, Lung, and Blood Institute. Dr. Criqui reported having no financial conflicts of interest.