A coronary artery calcium (CAC) scan can identify patients with type 2 diabetes who are at particularly high risk of a cardiovascular event as well as those with lower risk, according to a recent study in Diabetes Care, published online December 10, 2012.
The finding challenges the notion that all patients with type 2 diabetes have the same cardiovascular risk, says the study’s lead investigator, Donald Bowden, PhD. He says that measuring CAC is key to predicting the specific level of risk.
“People at very high risk are 11 times more likely to die from cardiovascular diseases as compared to those at low risk,” says Dr. Bowden, Professor of Biochemistry and Genomics and Personalized Medicine Research, Wake Forest University, Winston-Salem, North Carolina. Assigning a more precise risk level should help in the selection and intensity of therapy and also improve outcomes.
In the community-based Diabetes Heart Study, 1,123 persons with type 2 diabetes aged 34 to 86 years had CAC measured at baseline and were followed up for an average of 7.4 years for cardiovascular mortality. Sixteen percent of those enrolled were African American. Participants were recruited from internal medicine and endocrinology clinics in western North Carolina.
They were divided into five groups according to their baseline CAC scores derived from computed tomography scans (CAC scores 0–9, 10–99, 100–299, 300–999, and ≥1,000). Eighty-six participants had a CAC score ≥10).
Over the follow-up period, an assessment of death certificates revealed 92 cardiovascular disease (CVD) deaths. The incidence of CVD mortality increased as CAC scores increased.
Using the subjects with a CAC score of 0 to 9 as the reference group, the odds of CVD death were as follows among those with a score of:
- 10 to 99: 2.93 times
- 100 to 299: 3.17 times
- 300 to 999: 4.41 times
- 1,000 or more: 11.23 times
According to Dr. Bowden, the CAC score can be used as an adjunct to the Framingham risk score to reclassify CVD risk in patients with type 2 diabetes. The addition of CAC to the Framingham predictive model resulted in reclassification of 28% of the sample.
“Overall, 161 individuals in the entire cohort were reclassified to a higher risk category, with an event rate of 13.7%, and 159 were reclassified to a lower risk category, with an event rate of 6.9%,” the authors wrote.
Among intermediate-risk individuals, 53 (10%) were reclassified as high risk, and 144 (28%) were classified as low risk. In a model using the Framingham risk score alone, 54% of the cohort was classified in the highest or lowest risk categories, compared with 61% in a model that used the Framingham risk score plus CAC.
They concluded, “These findings suggest that CAC is a more reliable indicator of CVD risk than the established cardiovascular risk factors, probably because measuring the atherosclerotic plaque burden takes into account risk factors (both known and unknown) and their possible interactions.”
In an e-mail correspondence with Dr. Bowden, he wrote, “While standards of care for diabetes patients do indeed recommend statins, when we started the study only 50% of the subjects were on statins. This has now risen to 75%—better but still not enough. CAC is a very direct measurement of disease burden. The score and the CT image can /should have a high impact on patients that will improve recommended lifestyle changes and maintaining good medication.”
He added that when to use CAC is open to debate. “In our case we would assert that CAC is a much more powerful predictor of events and death than other conventional clinical measures,” he said. “The cost of the CT scan is $150 to $300, depending upon the provider—frankly, small change in clinical medicine.” Because CAC is a measure of what is happening in the “target” organ (the heart), “these kinds of data should motivate better care and intervention.”
The study was supported in part by the General Clinical Research Center of Wake Forest Baptist Medical Center, with a grant from the National Institutes of Health.