Coronary artery disease is a major cause of morbidity and mortality in patients with diabetes. This population has a high incidence of silent myocardial ischemia. As a result, coronary artery disease is usually more advanced at diagnosis in these patients than in the general population. By allowing earlier treatment, earlier diagnosis of coronary artery disease could significantly lower the death rate in this population. Earlier diagnosis of coronary artery disease may be achieved by screening for silent myocardial ischemia. In this study, Janand-Delenne and colleagues sought to define a high-risk diabetic population that could benefit from routine screening for silent myocardial ischemia.
The authors divided diabetic patients without symptoms of cardiovascular disease into two groups: patients with type 1 diabetes (formerly known as insulin-dependent diabetes) and patients with type 2 diabetes (formerly known as non–insulin-dependent diabetes). The patients were then screened for silent myocardial ischemia. First, an exercise electrocardiograph (ECG) was conducted. If the patient was able to complete the exercise test and the findings were normal, silent myocardial ischemia was considered to be ruled out. If the exercise testing was inconclusive or the patient was unable to complete it, thallium myocardial scintigraphy (TMS) was performed. If the findings of either test were positive, silent myocardial ischemia was confirmed or ruled out by coronary angiography.
Exercise ECG was successfully completed in 61.5 percent of patients, including 82 percent of patients with type 1 diabetes and 50 percent of patients with type 2 diabetes. Exercise ECG results were positive in 9.6 percent of patients. In patients unable to complete the ECG, TMS was performed. The TMS results were positive in 19 percent of these patients. A total of 10.9 percent of patients with type 1 diabetes had positive tests, with a 4.2 percent incidence of significant coronary stenosis (defined as greater than 50 percent vessel narrowing). In the type 2 diabetes group, 18.4 percent had positive screening tests, and angiography showed significant stenosis in 12.7 percent of patients.
The authors next classified patients who tested positive for silent myocardial ischemia on the basis of type of diabetes and sex. By far, the highest level of significant coronary artery stenosis was detected in men with type 2 diabetes, who exhibited a 20.9 percent incidence of significant stenosis. All other groups ranged between 2.3 and 7.4 percent significant stenosis by angiography. The authors correlated these results with a positive predictive value for these two screening tests for silent myocardial ischemia. They found that the positive predictive value of screening was 87.5 percent in men with type 2 diabetes but much lower in all other groups.
Based on these findings, about one in five asymptomatic male patients with type 2 diabetes will have silent myocardial ischemia with significant coronary stenosis. The authors believe, therefore, that routine screening for silent myocardial ischemia would be useful in this patient population. In addition, the increased risk of silent myocardial ischemia in this population necessitates active patient education to decrease some of the other risk factors for coronary artery disease.