Stress testing measures the heart's function with electrocardiography (ECG) while the heart is under stress, either from exercise or from a medication used to stress the heart.
Stressing the heart (by exercise or by use of stimulant medications 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 medication 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
DR P. MARAZZI/SCIENCE PHOTO LIBRARY
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, such as dipyridamole, dobutamine, adenosine, or regadenoson is injected to simulate the effects of exercise on the heart.
