SNOWMASS, COLO. – The use of coronary artery calcium screening in the subset of asymptomatic diabetes patients at higher clinical risk of CAD appears to offer a practical strategy for identifying a subgroup in whom costlier stress cardiac imaging may be justified, , said at the Annual Cardiovascular Conference at Snowmass.
The ultimate goal is to reliably identify those patients who have asymptomatic diabetes with significant CAD warranting revascularization or maximal medical therapy for primary cardiovascular prevention.
“Coronary artery calcium is a simple test that’s accessible and inexpensive and can give us a quick read on the extent of atherosclerosis in the coronary arteries,” said Dr. di Carli, professor of radiology and medicine at Harvard University in Boston. “There’s good data that in diabetic patients there’s a gradation of risk across the spectrum of calcium scores. Risk increases exponentially from a coronary artery calcium score of 0 to more than 400. The calcium score can also provide a snapshot of which patients are more likely to have flow-limiting coronary disease.”
Atherosclerotic cardiovascular disease is the biggest contributor to the direct and indirect costs of diabetes, and diabetes experts are eager to avoid jacking up those costs further by routinely ordering stress nuclear imaging, stress echocardiography, cardiac magnetic resonance, and other expensive noninvasive imaging methods unless they can be shown to lead to improved outcomes. There is general agreement on the value of noninvasive imaging in diabetic patients with CAD symptoms. However, the routine use of such testing in asymptomatic diabetic patients has been controversial.
Indeed, according to the 2017 American Diabetes Association Standards of Medical Care in Diabetes: “In asymptomatic patients, routine screening for coronary artery disease is not recommended as it does not improve outcomes as long as atherosclerotic cardiovascular disease risk factors are treated (). That’s a Level A recommendation.
But Dr. di Carli is among many cardiologists who believe this statement paints with too broad a brush. He considers it an overgeneralization that’s based on the negative results of two randomized trials of routine screening in asymptomatic diabetics: DIAD, which utilized stress single-photon emission CT (SPECT) imaging (), and FACTOR-64, which relied upon coronary CT angiography ( ). Both studies found relatively low yields of severe CAD and showed no survival benefit for screening. And of course, these are also costly and inconvenient tests.
The problem in generalizing from DIAD and FACTOR-64 to the overall population of asymptomatic diabetic patients is that both studies were conducted in asymptomatic patients at the lower end of the cardiovascular risk spectrum. They were young, with an average age of 60 years. They had a history of diabetes of less than 10 years, and their diabetes was reasonably well controlled. They had normal ECGs and preserved renal function. Peripheral artery disease (PAD) was present in only 9% of the DIAD population and no one in FACTOR-64. So this would not be expected to be a high-risk/high-yield population, according to Dr. di Carli, executive director of the cardiovascular imaging program at Brigham and Women’s Hospital, Boston.
An earlier study from the Mayo Clinic identified the clinical factors that can potentially be used to identify a higher-risk cohort of asymptomatic diabetic patients in whom high-tech noninvasive testing for significant CAD may be justified, he continued. This was a nonrandomized study of 1,427 asymptomatic diabetic patients without known CAD who underwent SPECT imaging. Compared with the study populations in DIAD and FACTOR-64, the Mayo Clinic patients had a longer duration of diabetes and substantially higher rates of poor diabetes control, renal dysfunction, hypertension, and dyslipidemia. One-third of them had PAD.
Fifty-eight percent of the 1,427 patients in the Mayo cohort proved to have an abnormal SPECT imaging scan, and 18% had a high-risk scan. In a multivariate analysis, the investigators identified several factors independently associated with a high-risk scan. Q waves were present on the ECGs of 9% of the asymptomatic diabetes patients, and 43% of that subgroup had a high-risk scan. Thirty-eight percent of patients had other ECG abnormalities, and 28% of them had a high-risk scan. Age greater than 65 was associated with an increased likelihood of a high-risk SPECT result. And 28% of patients with PAD had a high-risk scan.
On the other hand, the likelihood of a high-risk scan in the 69% of subjects without PAD was 14% ().
The 2017 ADA guidelines acknowledge this and similar evidence by providing as a relatively weak Level E recommendation: “Consider screening for CAD in the presence of any of the following: atypical cardiac symptoms (e.g., unexplained dyspnea, chest discomfort); signs of symptoms of associated vascular disease including carotid bruits, transient ischemic attack, stroke, claudication, or PAD; or electrogram abnormalities (e.g., Q waves).”
Dr. di Carli would add to that list age older than 65, diabetes duration of greater than 10 years, poor diabetes control, and a high burden of standard cardiovascular risk factors. And he proposed the coronary artery calcium (CAC) score as a sensible gateway to selective use of further screening tests, citing as support a report from the National Institutes of Health–sponsored Multi-Ethnic Study of Atherosclerosis (MESA).
The MESA investigators assessed CAC in 6,603 persons aged 45-84 free of known CAD at baseline, including 881 with diabetes. Participants were subsequently followed prospectively for an average of 6.4 years. Compared with diabetes patients who had a baseline CAC score of 0, those with a score of 1-99 were at a risk factor– and ethnicity-adjusted 2.9-fold increased risk for developing coronary heart disease during the follow-up period. The CHD risk climbed stepwise with an increasing CAC score such that subjects with a score of 400 or higher were at 9.5-fold increased risk ().
Using CAC measurement in this way as a screening tool in asymptomatic diabetes patients with clinical factors placing them at higher risk of significant CAD is consistent with appropriate use criteria for the detection and risk assessment of stable ischemic heart disease. The criteria were provided in a 2014 joint report by the American College of Cardiology, American Heart Association, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Failure Society of America, Heart Rhythm Society, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, and Society of Thoracic Surgeons.
The report rates CAC testing as “May Be Appropriate” for asymptomatic patients of intermediate or high global risk. As such, CAC “can be an option for further evaluation of potential SIHD [stable ischemic heart disease] in an individual patient when deemed reasonable by the patient’s physician,” according to the appropriate use criteria guidance, which was created with the express purpose of developing standards to avoid overuse of costly cardiovascular testing ().
Dr. di Carli reported having no financial conflicts.