Nuclear Stress Test

What is a nuclear stress test?

A nuclear stress test is a noninvasive imaging test that uses a tiny amount of radioactive material, known as a tracer. The tracer, which is injected into your arm, travels to your heart. The tracer emits a certain type of energy called gamma rays that can be detected by a special camera. The information is processed and reconstructed by computers to produce a clear picture of your heart. These images can show damage to the heart muscle and blood flow problems. There are many different names for this test. It is sometimes called a thallium test or a sestamibi test these are the two most common tracers used or your doctor may refer to it as radionuclide imaging, SPECT (which stands for single photon emission computed tomography), or myocardial perfusion imaging.

Some heart problems only show up when the heart is working hard (or stressed). A nuclear stress test is done while you exercise to see if there are any areas of your heart that do not get enough blood and oxygen when under stress. In women unable to exercise, a nuclear stress test may be performed using chemicals that mimic the effect of exercise on the heart.

Who might have a nuclear stress test?

Nuclear stress tests are generally used in women with symptoms suggestive of heart disease such as chest pain or shortness of breath, or those at risk for heart disease who had a previous abnormal test such as an ECG.

Who should not have a nuclear stress test?

If you are pregnant or breastfeeding, you should not have any kind of radiation procedure. If you have been diagnosed with inflammation of the heart muscle (myocarditis), recent lung infection, a birth defect causing a pinched or narrow aorta, severe narrowing of the aortic valve, or severe heart failure, you should also not have a nuclear stress test.

Test Procedure

How do I prepare for a nuclear stress test?

You should not smoke, eat, or drink anything for about four to six hours before the test. You may be asked to avoid caffeine for up to 24 hours before the test. If you have diabetes, you should discuss dietary concerns for the day of the test with your healthcare provider to moderate your blood sugar levels. Talk to your doctor about any medications or dietary supplements that you are taking because they may affect the accuracy of the test. You may have to stop taking or reduce the dosage of certain medications before the test. You may be unable to resume taking some medications until the tracer is cleared from your body (about 24 hours). You should wear comfortable, loose clothing and shoes appropriate for exercising.

What does a nuclear stress test entail?

You will strip from the waist up (you can keep your bra on) and put on a hospital gown. You will be hooked up to an ECG so that your heart rate can be monitored small sticky patches with wires attached will be taped to your body. The ECG also allows the technician to time the pictures for when the heart is moving the least; this reduces the chances of blurred images. To determine your target heart rate, the nurse will note your age, height, weight, and what medications you currently take. Depending on where the test is performed, the next step may vary. You will wear a blood pressure cuff for the exercise portion (running or walking on a treadmill). The exercise part may be done first, then the radioactive tracer is injected and pictures are taken. You may feel the needle prick when the intravenous (IV) line is inserted into your arm to administer the radioactive material. You will lie on the scanner bed with your arms overhead and a large camera will rotate 180 degree around you while taking multiple pictures. You must hold still when the pictures are taken to reduce the likelihood of blurring. After a few hours when your heart rate is back to normal, additional pictures are taken.

In one widely used test method, a radioactive tracer (usually thallium) is injected, and images are taken about 10 minutes later. You then exercise on a treadmill until you reach your predetermined target heart rate or until you ask to stop because of fatigue or pain. If you are unable to exercise, you will undergo a chemical stress test where a drug will be given to mimic the effects of exercise on the heart. When you reach your target heart rate with either chemical or exercise stress, a small amount of a different radioactive tracer (usually sestamibi) is injected. Fifteen to 30 minutes later, more pictures are taken. The first pictures taken show how blood flows to the heart during rest. The second set shows how the heart performs during exertion. Areas of the heart with normal blood flow appear light. Areas with reduced blood flow (indicating a blockage) absorb less of the tracer and appear dark.

How long does a nuclear stress test last?

The duration of the test will vary because of the different methods used. You should speak to your healthcare provider to find out how long your particular test will take. In most cases, it will take at least a few hours. At some facilities, the exercise portion and resting portion may be performed on different days.

What happens after a nuclear stress test?

After the test, you can eat, drink, and resume normal activities. You should drink plenty of fluids to flush the tracer from your body. If you don’t exercise regularly, you may experience chest pain, tiredness, muscle aches, and shortness of breath afterwards. If you had a chemical stress test, you may experience some minor side effects from the medication including nausea, heart palpitations, numbness in the arms or legs, flushing, chest pain, or headaches. A preliminary report may be available right after the test, but the complete results will not be ready for a day or more.

Test Results

What does a negative (normal) nuclear stress test indicate?

Women with a negative (normal) nuclear stress test have a low risk of developing future heart problems including heart attack. In women who have been diagnosed with heart disease, a normal nuclear stress test suggests a less than 1% annual risk of dying or having a heart attack. Women with diabetes and a normal nuclear stress test have a low risk of heart problems in the next 2 years, but their risk may rise sharply after that so they should have a follow-up test sooner than a woman without diabetes.

What does a positive (abnormal) nuclear stress test indicate?

The tests can be mildly, moderately, or severely abnormal. The risks of future problems increase with each category. Some but not all studies suggest that women with a positive (abnormal) test have a higher risk of dying or having a heart attack than men with an abnormal test, particularly when the test is severely abnormal. Your healthcare provider will discuss the results with you and prescribe further tests or treatments.

If you had nuclear stress test that involved exercise, your fitness level and response to exercise can tell a lot about your risk for future heart problems; see Exercise ECG for details.

Are nuclear stress tests accurate?

Images may be blurred in women who are obese, have smaller hearts, or large breasts. If you are obese or have large breasts, the extra tissue may muffle the radioactive energy of the tracer, making it appear that it is not being absorbed as well. This could cause a false positive result the test indicates a problem but in reality there is none. Modern nuclear stress tests include computer programs that correct for some of this blurring and muffling. In addition, timing the pictures for when the heart is moving the least (ECG gating) improves the quality of the nuclear stress test image. When these techniques are used, nuclear stress testing has a similar accuracy in men and women.  Of the radioactive tracers used, thallium is less accurate in women than sestamibi because it is more likely to be muffled by breast tissue.

Risks & Limitations

Are there any risks associated with nuclear stress tests?

The tests involves exposure to radiation. The amount of radiation you are exposed to during cardiac diagnostic tests is considered safe. The benefits of the test far outweigh any potential risks, and the technicians are trained to minimize your radiation exposure. For information on radiation safety, see National Institutes for Health Radiation Fact Sheet.

Does the nuclear stress test have any limitations?

If you are obese or have large breasts, the tissue may muffle the radioactive energy of the thallium or sestamibi, making it appear that it is not being absorbed as well, leading to a false positive—the tests detects a problem but in reality there is none. Some obese patients may be too heavy for the scanner table; the weight limit is about 300 pounds (lbs).

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