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Rethinking
the Treadmill Test
Excerpt
By Alison McCook,
Reuters Health
One of the most commonly used tests
to determine heart risk--the treadmill exercise test--may yield
just as much information after exercise as it does during the
workout, a new study suggests.
People with certain heart rate
irregularities that appear immediately after exercise have an
increased risk of dying within five years compared with those
who don't have such problems, according to the report in Thursday's
issue of The New England Journal of Medicine.
These findings suggest that exercise
tests, used for 50 years to detect heart disease, yield as much
information after the test is over as while it is taking place.
The finding may help doctors pick up certain heart abnormalities
in those at risk, including people with diabetes and those with
chest pain.
"There is a second part of the
exercise test, and that is the period after exercise," study author
Dr. Michael S. Lauer told Reuters Health.
In the current study, Lauer and
his colleagues found that people with a series of irregular heart
beat patterns called premature ventricular complexes (PVCs) that
appear after exercise are 50% more likely to die in a five year
period than people without those abnormalities.
Many people with PVCs are not aware
they have heartbeat irregularities, Lauer said. Most adults are
at low risk of this condition, he noted, but for those who are--such
as people with symptoms like chest pain, and certain conditions
like diabetes--a simple exercise test can tell.
"The exercise test is an enormously
powerful tool," said Lauer, of the Cleveland Clinic Foundation
in Ohio.
During the current study, 29,244
adults underwent exercise testing, in which researchers measured
their heart rate, blood pressure, and cardiac electrical activity
during and after the use of a treadmill.
Lauer and his team checked to see
if any of the participants developed frequent PVCs, defined as
changes in the heart's electrical activity that can result in
irregular and potentially deadly abnormalities in the heart rhythm.
About 7% of study participants
showed signs of PVCs during exercise, after exercise, or both.
Those with heart abnormalities that appeared during exercise,
however, showed no increased risk of death relative to those without
PVCs.
Lauer explained that the heart
is subject to a lot of electrical stimulation during exercise,
and it is the job of the brain to tell the organ to slow down
once exercise stops. The brain quiets the heart via the vagus
nerve, he said; but as the current study findings show, this attempt
to quell the heart after exercise does not always work.
"In a lot of people, that calming
mechanism is not working properly," he said.
This inability to calm the heart
may prevent the organ from reacting well to other stresses, he
suggested. For instance, a heart that has a block in the artery
that feeds it can experience a reduction in blood flow. A heart
with a healthy vagus nerve may overcome this particular stress,
he said, but a heart with an unhealthy vagus nerve may not.
If a person has PVCs after a period
of exercise, Lauer recommended that he receive an echocardiogram
to determine if he needs treatment to correct problems in the
heart's pumping ability. In addition, Lauer said that doctors
should urge patients with PVCs to control all other conditions
that put them at risk, such as high blood pressure and diabetes.
In an accompanying editorial, Drs.
Gregory D. Curfman of the journal and L. David Hillis of the University
of Texas Southwestern Medical Center in Dallas note that the current
results, by demonstrating the importance of monitoring patients
after the exercise test, "bring a new dimension to cardiac exercise
testing."
SOURCE: The New England Journal
of Medicine 2003;348:781-790,775-776.
Reference
Source 89
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