Stress testing evaluates the heart's function, the movement of its walls as it contracts, and the amount of blood flow it receives using electrocardiography (ECG), echocardiography, radionuclide imaging, or magnetic resonance imaging (MRI) while the heart is under stress, either from exercise or from a medication used to simulate the effects of exercise.
Stressing the heart (by exercise or by use of medications either to make the heart beat faster and more forcibly, or to directly increase blood flow to the heart muscle as during exercise) can help identify coronary artery disease. If the coronary arteries are partly blocked by coronary artery disease, the heart muscle 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.
Cardiac stress testing is similar to cardiopulmonary exercise testing, but the focus of cardiac stress testing is usually to identify coronary artery disease, while the focus of cardiopulmonary exercise testing is usually to understand the cause of symptoms or to evaluate exercise capacity in people with known heart or lung 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 or directly increasing blood flow to the heart muscle, 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.
The tests that can be done to identify inadequate blood flow include electrocardiography, echocardiography, radionuclide imaging, and MRI. Each has its advantages and disadvantages.
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. These false-positive results are more common with stress electrocardiography and stress echocardiography and 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
This photo shows a man undergoing exercise stress testing on a treadmill.
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.
For people who cannot achieve a high enough heart rate during exercise, a medications such as dipyridamole, dobutamine, adenosine, or regadenoson is injected to simulate the effects of exercise on the heart. Medications may increase how fast and strong the heart beats or they may artificially open the coronary arteries to increase blood flow to the heart.
The imaging method chosen by the doctor (echocardiography, radionuclide imaging, or MRI) will be performed before and after the stress (exercise or medication).
Testing can take 30 minutes to several hours, depending on the type of stress test done. Exercise stress testing has a small risk. Cardiac stress testing may cause a heart attack or death in a very small percentage of people tested.
