Silent ischemia is common in asymptomatic patients with type 2 diabetes

More than one in five patients older than 50 years with type 2 diabetes who have no symptoms of coronary artery disease (CAD) had silent myocardial ischemia on stress myocardial perfusion imaging, according to authors of the Detection of Ischemia in Asymptomatic Diabetics (DIAD) study. Furthermore, traditional cardiac risk factors were not associated with abnormal stress tests.

According to the authors, led by Frans J.Th. Wackers, MD, professor and director, cardiovascular nuclear imaging and exercise laboratories, Yale University, New Haven, Conn., “…this study indicates that totally asymptomatic patients with diabetes have at least an intermediate probability of CAD, a prevalence that may justify screening by noninvasive testing such as stress myocardial perfusion imaging.”

As reported in Diabetes Care (2004;27[8]:1954-1961), the DIAD study was designed to assess the prevalence and clinical predictors of silent myocardial ischemia in asymptomatic patients with type 2 diabetes using adenosine-stress single-photon emission-computed tomography (SPECT) myocardial perfusion imaging. All patients were recruited from diabetes and primary care outpatient practices. For this analysis, 522 patients aged 50 to 75 years with type 2 diabetes in whom angina was ruled out by questionnaire underwent SPECT imaging. Patients were under reasonable metabolic control (mean A1c = 7.1%) at entry. Fifteen percent of the study group was African American, a group that was lacking in prior screening studies, note the authors.

Overall, 113 patients (22%) of the cohort had abnormal SPECT studies, including regional perfusion abnormalities in 16% and markedly abnormal perfusion images with moderate or large stress defects in 6%. In addition, 6% had normal myocardial perfusion but had other significant test abnormalities, such as transient ST-segment depression, left ventricular dysfunction, or transient ischemic left ventricular dilation.

The strongest predictor of an abnormal stress test was a diminished heart rate response to the Valsalva maneuver. Moderate or large perfusion abnormalities were strongly associated with a decreased Valsalva response, male sex, and symptoms of autonomic neuropathy. Traditional cardiac risk factors or inflammatory or prothrombotic markers were not predictive of silent ischemia or perfusion abnormalities.

The authors note that the American Diabetes Association (ADA) recommends screening (by stress testing) of patients with two or more CAD risk factors, but in this study, “markedly abnormal myocardial perfusion results occurred with

equal frequency among patients with two or more and less than two risk factors.” Selecting only those patients for screening who had met ADA guidelines would have failed to identify 41% of the patients with silent ischemia.

They add that cardiac autonomic function testing “may have an important role in the CAD risk assessment of patients with type 2 diabetes because of the important association shown in this study.”