No benefit from screening asymptomatic type 2 diabetics for CAD

Should patients with type 2 diabetes be screened for coronary artery disease if asymptomatic? In the DIAD study (Detection of Ischemia in Asymptomatic Diabetics), 1123 patients with type 2 diabetes and no symptoms of coronary artery disease (CAD) were randomly assigned to be screened with adenosine-stress myocardial perfusion imaging (MPI) or to no screening. The main outcome measure was the incidence of cardiac death or nonfatal myocardial infarction (MI) during long-term follow-up.

The cumulative cardiac event rate was 2.9% over a mean follow-up of 4.8 years for an average of 0.6% per year. Seven nonfatal MIs and eight cardiac deaths (2.7%) occurred among the screened group, and ten nonfatal MIs and seven cardiac deaths (3.0%) among the group that received no screening (p=.73). However, of the patients who underwent screening, those with normal results (n=409) and those with small MPI defects (n=50) had lower event rates than the 33 with moderate or large MPI defects (0.4% vs 2.4% per year, p=.001).

Therefore screening using SPECT appeared to make no difference to the rate of coronary events in this study, and the event rate overall was low, which translates into a high cost of screening per event prevented. Indeed a low event rate was also seen in the recent ACCORD (Action to Control Cardiovascular Risk in Diabetes), leading some to question whether diabetic patients should truly be labelled as having the same risk as patients who have already had coronary events. For example, the ARIC (Atherosclerosis Risk in the Community) study found a lower mortality rate amongst diabetics than amongst patients with known coronary disease.

· Young LH, Wackers FJ, Chyun DA, et al. Cardiac outcomes after screening for asymptomatic coronary artery disease in patients with type 2 diabetes. JAMA 2009; 301: 1547-1555.

· Wackers FJ, Young LH, Inzucchi SE, et al. Detection of silent myocardial ischemia in asymptomatic diabetic subjects: the DIAD study. Diabetes Care 2004; 27: 1954-1961