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Stress Testing

by Michael J. Shea, MD

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.

Stress testing has two components. Exercise or a drug is used to stress the heart, 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 coronary artery disease, such as low blood pressure, shortness of breath, and chest pain.

To stress the heart, most people walk on a treadmill or pedal an exercise bicycle. Gradually, the pace of the exercise and the force required to do it (workload) are increased. The electrocardiogram (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. Testing takes about 30 minutes. Exercise stress testing has a small risk. The chance of its causing a heart attack or death is 1 in 5,000.

People who cannot exercise enough to do the test can be evaluated using pharmacologic stress testing. For this procedure, a drug, such as dipyridamole , dobutamine , or adenosine , is injected to simulate the effects of exercise on the heart.

Most commonly in stress testing, 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 (see Other Tests for Heart and Blood Vessel Disorders : Radionuclide Imaging).

No test is perfect. Sometimes, these tests show abnormalities in people who do not have coronary artery disease (a false-positive result), and 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.

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