CT Measurements May Help Predict Incident Cardiovascular Events

January 15, 2014

Using CT to measure coronary artery calcium may aid physicians in predicting the chances of incident cardiovascular events.

Computed tomography measurements of coronary artery calcium (CAC) has a strong predictive value for incident cardiovascular events, according to a study published in JAMA.

New data has been suggesting that increased plaque calcium density may be protective for cardiovascular disease, so researchers from California, Washington, Pennsylvania, and Tennessee, used data obtained from the prospective, observational MESA study (Multi-Ethnic Study of Atherosclerosis) to determine the independent associations of the CAC volume and density with incident cardiovascular disease events. The researchers hypothesized that greater CAC density would be inversely related to incident cardiovascular disease events.

A total of 3,398 men and women, aged 45 to 84, participated in the study. They were from four race/ethnicity groups (non-Hispanic white, African American, Hispanic, and Chinese). All were free of known cardiovascular disease at baseline, had CAC greater than 0 on their baseline CT, and were followed up through October 2010. The CAC measurements were obtained twice for each patient, both with the same method used by that facility.

The subjects were followed from baseline to first cardiovascular disease event, loss to follow-up, or the ninth follow-up call. The two endpoints were hard coronary heart disease (CHD), which was defined as myocardial infarction, resuscitated cardiac arrest, or CHD death; and hard cardiovascular disease, defined as hard coronary heart disease, stroke, or stroke death.

The results showed that at a median of 7.6 years of follow-up, there were a total of 265 cardiovascular disease events. “With both lnCAC volume and CAC density scores in the same multivariable model, the lnCAC volume score showed an independent association with incident [coronary heart disease], with a hazard ratio (HR) of 1.81 (95 percent CI, 1.47 to 2.23) per standard deviation (SD = 1.6) increase, absolute risk increase 6.1 per 1,000 person-years, and for [cardiovascular disease] an HR of 1.68 (95 percent CI, 1.42 to 1.98) per SD increase, absolute risk increase 7.9 per 1,000 person-years,” the authors wrote. “Conversely, the CAC density score showed an independent inverse association, with an HR of 0.73 (95 percent CI, 0.58 to 0.91) per SD (SD = 0.7) increase for [coronary heart disease], absolute risk decrease 5.5 per 1,000 person-years, and an HR of 0.71 (95 percent CI, 0.60 to 0.85) per SD increase for [cardiovascular disease], absolute risk decrease 8.2 per 1,000 person years.”

There was significantly improved risk prediction with the addition of the density score to a model containing the volume score for both coronary heart disease and cardiovascular disease  in the intermediate cardiovascular disease risk group.

“CAC is present in more than half of middle-aged US residents and by age 70, the probability of CAC exceeds 90 percent,” the authors noted. “Many patients have had serial CAC scans to evaluate progression. The use of the Agatston score in assessing CAC progression is problematic since an increase in CAC could be due to an increase in volume, an increase in density, or both.”  The Agatston method is the current standard methodology for scoring the amount of CAC from CT scans. The Agatston score is weighted upward for greater CAC density because the score the product of the within-slice CAC plaque area and a plaque-specific density factor of 1, 2, 3, or 4, summed for all cardiac CT slices.

The researchers concluded that CAC volume was positively and independently associated with coronary heart disease and cardiovascular disease risk. At any level of CAC volume, CAC density was inversely and significantly associated with coronary heart disease and cardiovascular disease risk. The role of CAC density should be considered when evaluating current CAC scoring systems.