Stress Testing
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Stressing the heart (by exercise or by use of stimulant
drugs to make the heart beat faster and more forcibly) can help identify
coronary artery disease. In coronary artery disease, blood flow through the
coronary arteries (which supply blood to the heart muscle) is partly or
completely blocked. If the coronary arteries are only partly blocked, the heart
may have an adequate blood supply when the person is resting but not when the
heart is working hard. Thus, testing the heart during stress can help identify
coronary artery disease.
Because exercise stress testing specifically monitors how the
heart is functioning, the testing helps doctors distinguish between problems
due to a heart disorder and those due to other problems that limit exercise,
such as lung disorders, anemia, and poor general fitness.
During stress testing, exercise or a drug is used to stress
the heart, typically making it beat faster, and the person is tested for signs
of inadequate blood flow to the heart. The person is also monitored for
symptoms that suggest inadequate blood flow to the heart, such as low blood
pressure, shortness of breath, and chest pain.
Most commonly in stress testing, electrocardiography (ECG)
is used to check for reduced blood flow in coronary arteries. Sometimes, more
accurate but more expensive tests, such as echocardiography and radionuclide
imaging, are done as part of stress testing.
No test is perfect. Sometimes these tests show abnormalities
in people who do not have coronary artery disease (a false-positive result).
Sometimes tests do not show any abnormalities in people who have the disease (a
false-negative result). In people without symptoms, especially younger people,
the likelihood of coronary artery disease is low, despite an abnormal test
result. In such cases, a positive result is usually more likely to be false
than true. These false-positive results may cause considerable worry and
medical expense. For these reasons, most experts discourage routine exercise
stress testing (such as for screening purposes before an exercise program is
begun or during an evaluation for life insurance) in people who do not have
symptoms.
How stress testing is done
To stress the heart using physical exercise, most people
Walk on a treadmill
Pedal an exercise bicycle
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Gradually, the pace of the exercise and the force required
to do it (workload) are increased. The ECG is monitored continuously, and blood
pressure is measured at intervals. Usually, the person being tested is asked to
keep going until the heart rate reaches between 80% and 90% of the maximum for
age and sex. If symptoms, such as shortness of breath or chest pain, become too
uncomfortable or if significant abnormalities appear on the ECG or blood
pressure recordings, the test is stopped sooner.
In some people, doctors will do tests other than ECG, such
as echocardiography and radionuclide imaging, right after the person completes
the exercise to detect whether the heart is receiving enough oxygen. These
tests are used when doctors have a greater suspicion that coronary artery
disease is present or when results from the ECG are unclear.
Testing can take 30 minutes to several hours, depending on
the type of stress test done. Exercise stress testing has a small risk. The chance
of its causing a heart attack or death is 1 in 5,000.
Doctors stress the heart using drugs (pharmacologic stress
testing) in people who cannot exercise enough to do the test. For this procedure,
a drug, can be is injected to simulate the effects of exercise on