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'
"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.