Cardiac computed tomography and myocardial perfusion imaging for risk stratification in asymptomatic diabetic patients: A critical review

Diabetes is a major cause of mortality and morbidity worldwide, and its prevalence is increasing at alarming proportions. Coronary artery disease (CAD) accounts for 70% of the deaths among diabetic patients. Patients with diabetes have a 2-to-4-fold higher risk of cardiac events than their nondiabetic counterparts. In fact, the risk of myocardial infarction in diabetic patients without previous CAD is comparable to the risk of reinfarction in nondiabetic subjects with previous CAD. Furthermore, patients with diabetes are less likely to survive a first myocardial infarction (MI) than those without diabetes, and those who survive the first MI face a higher risk of reinfarction. Hence it is crucial to diagnose CAD at an early subclinical stage in patients with diabetes, so that high-risk patients can be targeted for aggressive management. The search for a robust, noninvasive technique to screen asymptomatic diabetic patients has been a focus of research, and the potential role of noninvasive techniques such as coronary artery calcium (CAC) imaging and myocardial perfusion imaging (MPI) has triggered controversy and several interesting debates. On the one hand, any strategy involving the use of screening may spiral healthcare budgets out of control, and there is no strong evidence from prospective, randomized trials that a particular strategy can improve clinical outcomes. Diamond et al, in their recent essay on this controversial subject, highlighted the great difficulty in conducting a prospective, randomized trial to evaluate the cost-effectiveness of screening asymptomatic diabetic subjects. They estimated that such a trial would require the randomization of 80,000 subjects followed for 5 years, i.e., a huge investment of resources in view of the small differences in projected outcomes. On the other hand, in diabetic patients, CAD is often asymptomatic and can be well-advanced by the time of presentation. Therefore, it may be negligent to ignore these patients when diabetes is considered a “surrogate” for CAD. It is worth noting here that lack of evidence of effect does not necessarily imply evidence of lack of effect. In the absence of prospective trials exploring the clinical effectiveness and cost-effectiveness of screening strategies for asymptomatic diabetic subjects, we examined the available evidence from several studies that may provide a basis for future trials.