Diabetic patients without coronary artery calcium (CAC) are at a relatively low risk for coronary heart disease (CHD) despite the duration of their diabetes, according to new a new study in JAMA Cardiology.
The research suggests CAC scores could be a useful addition to global assessment tools for CHD risk stratification in patients with diabetes and metabolic syndrome. Adding CAC scores to Framingham Risk Score (FRS), ethnicity/race and socioeconomic status improved risk classification by 23 percent in people with diabetes, 22 percent in those with metabolic syndrome and 25 percent in individuals with neither condition.
Lead researcher Shaista Malik, MD, PhD, MPH, and colleagues followed 6,751 patients for an average of 11.1 one years and assessed CHD events as a composite of MI, resuscitated cardiac arrest and CHD death. The study population was 62 years old on average, 53 percent women and ethnically diverse—38.5 percent white, 27.5 percent African-American, 22.1 percent Hispanic and 11.9 percent Chinese.
“Many individuals with diabetes are at lower CHD and ASCVD (atherosclerotic cardiovascular disease) risk than is widely understood and are not at high risk or CHD risk equivalents,” Malik et al. wrote. “Our results also indicate that CAC scoring adds significant clinical utility in further stratifying and reclassifying risk in persons with MetS (metabolic syndrome) and diabetes beyond global risk assessment using the FRS or ASCVD Pooled cohort risk score. Moreover, we found that the severity of CAC appears to be a more important clinical prognostic indicator than measures of disease severity, such as insulin use, glycemic control, and diabetes duration.”
In multivariable analyses, CAC scores were independently associated with 30 percent greater CHD risks in individuals with diabetes and metabolic syndrome and a 37 percent greater risk for people with neither condition. The researchers noted a stepwise growth in risk as CAC scores increased.
CAC is measured by noncontrast CT and can be used to identify subclinical atherosclerosis. But according to the authors, “most prior studies that examined risk classification have excluded those with diabetes because the diagnosis of diabetes carries a label of CHD risk equivalency, whereas prediction models offer less clinical utility.”
Even though CAC and other risk factors were only measured at baseline for this study, Malik and colleagues reported the absence of CAC in patients with long-standing diabetes was associated with similarly low rates of CHD events as those with shorter durations of diabetes. For people with diabetes but no CAC at baseline, the CHD event rate was 3.7 per 1,000 person-years.
“Although diabetes is known to accelerate the aging process, future studies need to focus on the factors that provide resilience among patients with lack of subclinical disease despite long-standing diabetes,” the authors wrote.
The authors noted patients and physicians were made aware of their CAC imaging results, which may have caused them to attempt to modify risk factors. But if this were the case, it would only lessen the strength of the study’s findings.