June 10, 2011
Dear Mayo Clinic:
My husband's doctor suggested he should do a nuclear stress test that will look at his heart. What does it involve? Are there any risks? He is 68.
A nuclear stress test measures blood flow to the heart muscle both at rest and during stress on the heart. Nuclear stress tests are usually done to evaluate the possible presence of coronary artery disease. The test can be done while a person is exercising or by using a drug that increases blood flow to the heart. Any stress test has some potential risks, but the possibility of having complications due to a nuclear stress test is quite small.
Many people use the term "stress test" to refer to a stress electrocardiogram. This test requires a person to walk on a treadmill while heart rhythm, blood pressure and breathing are monitored with an electrocardiogram. A nuclear stress test includes all the components of a stress electrocardiogram, but it also involves taking two sets of heart images — one at rest and another after exercise.
For a nuclear stress test, sticky patches (electrodes) are placed on the chest, legs and arms. The electrodes are connected by wires to an electrocardiogram machine. The electrocardiogram records the electrical signals that trigger heartbeats. A blood pressure cuff is placed on one arm to monitor blood pressure during the test.
The person being evaluated then begins walking slowly on the treadmill. As the test progresses, the speed and incline of the treadmill increases. In general, the person undergoing the test exercises until she or he either shows evidence on the electrocardiogram of a heart problem or experiences symptoms such as chest pain, shortness of breath or fatigue.
Typically, a specific heart rate isn't used as a target during nuclear stress tests because changes in heart rate during exercise vary significantly from one person to another, depending on age and other factors such as fitness level, medications or underlying medical conditions.
People who are unable to exercise may instead be injected with a medication that increases blood flow to the heart muscle — similar to what exercise does.
Once the maximum level of exercise is reached, a radioisotope is injected into the patient's bloodstream. The radioisotope mixes with the blood and travels to the heart. A special scanner similar to an X-ray machine — which can detect the radioactive material — is used to create images of the heart muscle during stress. That image is compared to a picture of the heart at rest. The resting heart image usually is obtained before the test, but in some cases it may be done afterward.
As with any medical procedure, some risks are associated with a nuclear stress test, but they are uncommon. Possible risks include low blood pressure during or after exercise that causes dizziness or light-headedness and abnormal heart rhythms triggered by exercise that may require treatment. Some people worry that a stress test could cause a heart attack. Although that is possible, it's very rare.
To decrease the risks, doctors carefully evaluate patients before a stress test to make certain they can safely undergo the procedure. In addition, during the test, your husband would be closely monitored to ensure his safety.
A nuclear stress test can be a helpful part of evaluating chest pain and other symptoms of coronary artery disease. The test results can give your husband's doctor useful information to identify possible heart problems and, if necessary, develop a treatment plan. Although a small amount of risk is involved, in most cases the benefits of having a nuclear stress test far outweigh those risks.
— Raymond Gibbons, M.D., Cardiovascular Diseases, Mayo Clinic, Rochester, Minn.