Screening for Asymptomatic CAD in Diabetic Patients Does Not Reduce Cardiac Events

April 15, 2009

April 15, 2009 (New Haven, Connecticut) — Screening for asymptomatic coronary artery disease in patients with type 2 diabetes fails to significantly reduce future cardiac events, according to the results of a new study [1]. In light of the findings, the researchers conclude that routine screening for inducible ischemia in asymptomatic patients with diabetes mellitus should not be advocated.

"Routine screening is not justified because what you end up finding is relatively mild, and screening did not make a difference," senior investigator Dr Frans Wackers (Yale University School of Medicine, New Haven, CT) told heartwire . "Both groups, whether they had screening or not, did equally well. Also, the event rate we observed is very low, so the cost of screening to prevent myocardial infarction would be very high. It isn't cost-effective."

The results of the study, known as the Detection of Ischemia in Asymptomatic Diabetics (DIAD) trial, are published in the April 15, 2009 issue of the Journal of American Medical Association.

Screening is Controversial

Speaking with heartwire , Wackers said that the current standard of care for patients with diabetes is to reduce cardiovascular risk factors. There has been a growing interest, however, in the early detection of asymptomatic coronary artery disease with screening in these patients.

"We always have had the feeling that we're behind the curve in patients with diabetes--in particular, that these patients might not have the same symptoms as other heart-disease patients," said Wackers. "The notion is that we have to do something to detect the disease in these patients much earlier, so that we can treat it earlier and have better outcomes."

In this prospective study, the DIAD investigators randomized 1123 diabetic patients with no coronary artery disease symptoms to screening with adenosine-stress radionuclide myocardial perfusion imaging (MPI) or to no screening. Investigators reported in 2004 that ischemic abnormalities were detected in 25% of patients [2], but the silent myocardial ischemia was not "terribly alarming," said Wackers. Severe abnormalities on the stress test occurred in approximately 6% of patients.

Patients were then followed for an average of 4.8 years. Overall, the cumulative cardiac event rate was just 2.9% during follow-up, or an average of 0.6% per year. There were 15 events in the screening group and 17 events among those who weren't screened, a statistically nonsignificant difference. Similarly, there was no difference in any of the secondary end points, which included angina, heart failure, stroke, and revascularizations.

Wackers noted that the overall rate of coronary revascularization was low in both groups, at 5.5% in the screened group and 7.8% in the unscreened group, so this did not explain the low rates of cardiac events in the study. Most likely, he told heartwire , changes in the guidelines for the treatment of diabetic patients that occurred during the course of the study affected the event rates. Patients with diabetes are now treated similarly to patients with coronary artery disease, and in this study were prescribed aspirin, statins, and antihypertensive drugs and received recommendations for lifestyle modification.

"At five years, we saw that between 70% and 80% of patients were receiving primary-prevention care, and although we can't prove it, it is very likely that this aggressive treatment had something to do with the very low cardiac event rate observed in this study," said Wackers.

Instead of screening, diabetic patients without symptoms of coronary artery disease should be followed closely, said Wackers. Only if something changes should the patient receive diagnostic testing and be treated accordingly, he said.

Cardiac event rates did differ significantly according to the results of the stress MPI test. In the screened cohort, the 459 subjects with normal results and small MPI defects had significantly lower cardiac event rates than the 33 individuals with moderate or large defects. However, the event rate among these subjects is still low at 2.4% per year, and the moderate or large MPI defects on screening had a positive predictive value of just 12%.

Low Event Rates

Dr Sanjay Kaul (Cedars Sinai Medical Center, Los Angeles, CA), who commented on the results of the study for heartwire , noted that the DIAD trial is the first to prospectively address the issue of systematic screening for inducible ischemia in an unselected, unbiased, asymptomatic patient population with type 2 diabetes mellitus.

"While SPECT accurately characterized high- and low-risk patients, it failed to identify patients with improved outcomes," commented Kaul. "These observations, together with the potentially prohibitive cost considerations, argue against recommending and implementing stress SPECT imaging as a screening program in millions of asymptomatic subjects with type 2 diabetes mellitus at the present time. It does, however, provide support for 'unconditional treatment' as an effective strategy in this population."

The recently published Action to Control Cardiovascular Risk in Diabetes (ACCORD) also reported low event rates, 1.4% per year, which makes DIAD consistent with that trial, said Kaul. These low event rates, coupled with findings from the Health Professionals Follow-up Study and the Atherosclerosis Risk in Communities Study, where there was lower reported coronary or cardiovascular disease mortality among diabetics than among patients with prior coronary heart disease, "challenge the notion of diabetes being classified as a CHD equivalent," added Kaul.

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