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Back To Vidyya Routine Exercise Tests Predict Death Risk

Study Shows Combining Tests' Results More Effective Than Electrocardiogram

Two results from routine exercise tests can be combined to predict risk of death from all causes in adults over a five-year period, according to a Cleveland Clinic study published today in the Journal of the American Medical Association.

"Although exercise testing has been commonly used for decades, doctors have been focusing primarily on the electrocardiogram, instead of other, simpler measures which actually give more useful information," said Michael S. Lauer, M.D. "When the exercise test is interpreted correctly, it may well be one of the most powerful and cost-effective measures of health we have."

Dr. Lauer is Director of Clinical Research in the Department of Cardiology at The Cleveland Clinic Foundation. He also directs the Exercise Testing Laboratory. Dr. Lauer has received funding from the American Heart Association for exercise test research. He has not received funding from private corporations interested in exercise testing.

Cleveland Clinic investigators studied 9,454 patients who underwent exercise testing between 1990 and 1998. The patients were followed on average for five years, during which time 312 died. Two stress test results that accurately predicted mortality risk were the amount the heart rate fell during the first minute after exercise and the length of time that the patient exercised until exhaustion.

The first measurement is heart rate recovery, Dr. Lauer explained. That measurement is taken by recording the heart rate when the patients complete the test and again one minute later. The investigators found that in 20 percent of the patients, the heart rate fell by 12 beats per minute or less. Those patients were four times as likely to die, compared with patients whose heart rates fell by more than 12 beats per minute.

The other measurement is a treadmill score that is largely dependent on the amount of time a patient exercised on the treadmill. Patients had to be able to exercise for at least five to eight minutes on a progressively accelerating treadmill. This score ranked at high risk in 21 percent of patients; they also had a four-fold increased mortality risk.

"What was particularly interesting was what we observed when we combined both readings," Dr. Lauer said.

The risk of death was approximately 3 percent per year for the 10 percent of patients for whom both findings were abnormal, Dr. Lauer said. By comparison, that risk dropped to approximately 1 percent per year for the 27 percent of patients whose exercise test results showed one abnormal finding. Two-thirds of patients tested showed normal findings for both heart recovery and treadmill score. Their risk of death was 0.2 percent. Dr. Lauer said the test functioned as a way to predict death regardless whether the patient was tested after complaining of chest pains or other symptoms or was tested as part of a routine physical.

The exercise test is one of the most common non-invasive tests administered in the United States each year. Physicians traditionally have concentrated on the electrocardiogram obtained during the test, using it to determine whether the test is normal or not. Patients with abnormal electrocardiograms might be referred for other tests and specialists' evaluation.

"In fact, we found that the electrocardiogram tracings were the least useful piece of information obtained," Dr. Lauer said. "Our findings, along with those of researchers from other institutions, suggest that it is time that we radically change the way we read exercise tests, and in that way, better serve our patients."

Most patients who have a normal treadmill score and a normal heart rate likely do not need further tests or medication, Dr. Lauer noted. Patients who have abnormalities may then be candidates for further testing or treatment, Dr. Lauer observed.

"For many years, the idea of a 'screening' exercise test didn't make much sense to many of us in cardiology," Dr. Lauer said. "The current findings suggest, however, that there may be a good role for screening exercise tests, but only as long as we pay more attention to exercise time and heart rate changes, rather than the electrocardiogram."

Dr. Lauer joined the Cleveland Clinic in 1993. He received his MD from the Albany Medical College in Albany, N.Y., and completed training in Internal Medicine, Cardiology, and Clinical Effectiveness at Harvard Medical School, the Harvard School of Public Health, Massachusetts General Hospital, and Beth Israel Hospital, all in Boston. He specializes in clinical cardiology, exercise testing and cardiovascular epidemiology.

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Editor: Susan K. Boyer, RN
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