SOURCE: American Diabetes Association

June 08, 2008 12:30 ET

Silent Ischemia in Diabetes Not as Common Nor Threatening as Thought

Favorable 5-Year Outcome for Asymptomatic People With Type 2 Without Evidence of Coronary Artery Disease; Expensive Screening Not Needed When Standard Clinical Care and Follow-Up Attentive

SAN FRANCISCO, CA--(Marketwire - June 8, 2008) - Results of a nearly five-year study of more than 1,100 older adults with type 2 diabetes -- a group that is at risk for heart attacks or sudden death -- may let them breathe a little easier, according to a report presented here today at the American Diabetes Association's 68th Annual Scientific Sessions.

"We found that silent myocardial ischemia -- restriction of blood flow to the heart -- occurred in only 22% of the asymptomatic adults with type 2 diabetes that we screened, a far lower percentage than expected," said Frans J. Wackers, MD, PhD, Professor Emeritus, Diagnostic Radiology and Medicine, Yale University School of Medicine, in a recent interview. He led the Detection of Ischemia in Asymptomatic Diabetics (DIAD) study, which was conducted to assess the prevalence of such ischemia and discern whether expensive coronary artery disease screening used in the study should be offered to all people with type 2 diabetes. His conclusion: it's not justified.

"Over the course of the study, all participants continued to be seen by their own physicians, and the physicians of 30% of the unscreened control group independently found reason to recommend various diagnostic and treatment procedures, such as stress testing, cardiac catheterization, angioplasty, and bypass surgery, to their patients," said Dr. Wackers. "Since these control patients likely had an equal prevalence of ischemia to those who were screened, standard clinical care and attentive follow-up appear to be sufficient to detect those at risk and in need of intensive cardiologic care." After nearly five years, there was essentially no difference between the groups -- with the overall cumulative rate of cardiac events only 2.8%, which was much lower than anyone had expected.

Silent Ischemia

According to the National Institutes of Health, heart disease and stroke account for about 65% of deaths in people with diabetes. Adults with diabetes have heart disease death rates about 2 to 4 times higher than those without diabetes. Too many people arrive at hospitals with a heart attack -- their diabetes sometimes undiagnosed and with no prior warning that they have a cardiac problem. Some studies have shown that a diabetes diagnosis as an adult yields the same risk for a future cardiovascular event as a person without diabetes who has previously had one heart attack. The normal warning sign of a shortage of blood flow to the heart is the chest pain called angina. However, due to a common form of nerve damage in people with diabetes called neuropathy, that "warning" pain is often not felt or may only be experienced at such a low level that it is not perceived as a warning.

How widespread such silent myocardial ischemia is in people with diabetes has long been debated, with some studies suggesting the figure was as high as 60%. However, other researchers believed that studies showing high estimates were "contaminated" because they included people who went to the hospital for problems related to the heart.

DIAD Design

DIAD was designed to avoid problems seen in prior studies. Working with 14 diabetes clinics in the U.S. and Canada, study investigators recruited 1,123 adults with type 2 diabetes who had no cardiac symptoms, no previously diagnosed coronary artery disease, and normal electrocardiograms (ECGs). Participants were aged 55 to 75 years at the outset, with a mean diabetes duration of 8.7 years. Patients were randomly assigned to either the screening or control (no screening) group.

The Screening

The screening test used in the DIAD study was adenosine stress myocardial perfusion imaging (MPI), a standard test cardiologists perform to evaluate patients at high risk for coronary disease. The stress is not induced by walking on a treadmill, but by a medication called adenosine. Adenosine does not increase your heart rate. Rather, it dilates blood vessels leading into the heart, increasing blood flow, therefore simulating exercise for the patients.

The patient is given a 4-minute intravenous infusion with a radioisotope tag. If any area of the heart does not display increased blood flow, as it should under stress, then it will have less radioisotope displayed, which is an indicator of a defect. Three-dimensional radionuclide SPECT (single photon emission computed tomography) imaging of the heart, which takes about 45 minutes, enables the cardiologist to evaluate the significance of any defect.

All of this is done with the patient comfortably lying down. While this is a standard test, it requires an experienced person to interpret the results, and the test can cost up to several thousand dollars, depending on the area of the country where it is performed.

Detailed Findings

Of those screened at the outset, 22% had silent myocardial ischemia, of which only 6% of the defects were considered severe.

"When we sent the results to their physicians, we were afraid that all of these patients would be referred to cardiologists, which would damage the results of our study," said Dr. Wackers. "We honestly reported that we did not know what the findings meant, and we did not recommend treatment." The result was that only a small number of the ischemic patients were referred by their physicians for cardiac evaluation; some were found to have coronary artery disease and some went on to have bypass surgery.

All DIAD study participants were called every six months to check on their health, i.e. to determine whether they had developed any symptoms of cardiac problems, such as congestive heart failure, heart attack, or death.

"Over 4.8 years, there was essentially no difference between the two groups," reported Dr. Wackers. "Screening did not improve outcomes." The rate of cardiac events was a half percent per year, much lower than anyone had been expecting, for a cumulative rate of cardiac events of 2.8%. He believes this low rate is in small measure due to the cardiac procedures undertaken by a small number of ischemic patients -- both among the screened and the controls; 7% in both groups had bypass surgery. Nonetheless, the overall results bode well.

However, over the course of the study, the percentage of participants who were being treated by their physicians with aspirin, statins, and anti-hypertensive medications rose from 40% at the outset of the study to 75% at the close. "I think that rather than the surgical interventions, this optimized treatment explains why both groups did so well."

"Therefore, asymptomatic people with diabetes who do not have evidence of coronary artery disease have favorable five-year outcomes," he concludes. "The situation is not as bad as we thought, and we don't have to spend millions of dollars to screen everyone with diabetes with stress adenosine MPI, but they do have to be followed closely, with diagnosis and treatment done when any symptoms or other indications arise."

Nearly 21 million Americans have diabetes, a group of serious diseases characterized by high blood glucose levels that result from defects in the body's ability to produce and/or use insulin. Diabetes can lead to severely debilitating or fatal complications, such as heart disease, blindness, kidney disease, and amputation. It is the fifth leading cause of death by disease in the U.S. Type 2 diabetes involves insulin resistance -- the body's inability to properly use its own insulin. Type 2 occurs mainly in adults who are overweight and ages 40 and older.

The American Diabetes Association is the nation's leading voluntary health organization supporting diabetes research, information and advocacy. Founded in 1940, the Association has offices in every region of the country, providing services to hundreds of communities. For more information, please call the American Diabetes Association at 1-800-DIABETES (1-800-342-2383) or visit www.diabetes.org. Information from both these sources is available in English and Spanish.

Abstract #169-OR

NOTE TO EDITOR:

Visit http://www.diabetes.org/adablog to read blog posts from the Association's Scientific Sessions from former USA Today reporter, Anita Manning.

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