Feb. 24, 1999 DALLAS -- Researchers say that taking images of the heart using radioactive material after a traditional treadmill test may better identify those who are able to exercise for long periods of time, but are still at increased risk for heart attack, death, or the need for bypass surgery or balloon angioplasty.
While prior studies suggest that patients who demonstrate exercise endurance have a negligible risk of future heart problems, researchers say in a study published in Circulation: Journal of the American Heart Association that this is not always true.
"Overall, those who can exercise longer are a lower risk group for heart attacks than patients who aren't able to exercise as much," says the report's lead author, Sofia N. Chatziioannou, M.D., Ph.D., assistant professor and nuclear medicine specialist at Baylor College of Medicine and the St. Luke's Episcopal Hospital/Texas Heart Institute in Houston, Texas. "But we can identify through MPI those at relatively high risk of having a heart attack, sudden death, or the need for bypass surgery or balloon angioplasty to open clogged vessels."
Scientists say there is a subgroup of people who can exercise for long periods of time, but are still at significantly higher risk for heart problems. This group can be identified, they say, with the use of a test called treadmill myocardial perfusion imaging (MPI). The test uses small amounts of radioactive material to measure blood flow to the heart.
In MPI, after a person jogs on a treadmill, he or she is injected with radioactive material. According to Chatziioannou, doctors then utilize a "picture" or "scan" of the heart called a radioisotope image to see where and how much of the radioactive material is flowing to the heart.
Blood flow to the heart can be reduced by coronary artery blockages, fatty deposits or plaques lining the blood vessels. If a plaque ruptures, it can unleash a blood clot that can trigger heart attack or stroke.
The test identified those who were at risk for heart attack, death or need for heart surgery or balloon angioplasty but in whom the signs of heart disease on the standard treadmill exercise test were not useful, according to the researchers.
"People with abnormal MPI had an eight times higher chance of having a significant heart problem within one and a half years, compared to those with normal blood supply, even if they were able to exercise well," says Chatziioannou. "Almost four percent of those with abnormal test results died within this period, while nobody with a normal MPI test died."
While MPI may be more accurate, according to researchers, it is also five times more expensive than a regular treadmill test. Chatziioannou says MPI is a widely used diagnostic procedure and is available at most hospitals and many clinics.
"While there are likely specific subgroups who benefit from MPI, we don?t have enough clinical evidence to say that everybody should have MPI," says Chatziioannou.
The researchers compared MPI to a standard treadmill test. During exercise, the heart has to pump blood throughout the body more rapidly than when the individual is sedentary, so a treadmill exercise test is a good indicator of how well the heart is working. A person with heart disease may have an abnormal heart rate or electrocardiogram (ECG) -- a heart test which shows its electrical activity -- during the treadmill test.
The scientists selected 388 people who exercised for more than nine minutes without stopping. Of these, 337 were men and 51 women, whose ages ranged from 26 to 83. A total of 224 had heart disease. The scientists compared the results of ECG and the MPI scans taken immediately after treadmill testing with what happened to patients in the following months.
Of the 388 study participants, 231 had normal MPI and 157 showed abnormal blood flow. Similarly, 299 people had negative ECGs during exercise and 89 had positive tests. Nineteen patients had bypass surgery or balloon angioplasty as a result of their initial screenings and were not included in the further analysis.
Of the remaining 369 patients, 16 required bypass surgery or angioplasty, two suffered nonfatal heart attacks, and three died from heart attacks. About 2 percent of patients -- four of 230 -- with normal MPI, and 12.2 percent -- 17 of 139 -- with abnormal scans had some sort of heart problem. Five of 81 patients (6.2 percent) with positive ECGs during exercise and 16 of 288 (5.5 percent) with negative ECGs experienced heart problems.
Chatziioannou notes, however, that only 13.1 percent of the study participants were women, and as a result, it remains an open question whether the findings apply equally to women. "We think our findings apply mainly to men," she says.
Co-authors are Warren H. Moore, M.D.; Patrick V. Ford, M.D.; Ronald E. Fisher, M.D., Ph.D.; Vei-Vei Lee, M.S.; Carina Alfaro-Franco, M.D.; and Ramesh D. Dhekne, M.D.
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