A nuclear stress test uses radioactive dye and an imaging machine to create pictures showing the blood flow to your heart. The test measures blood flow while you are at rest and are exerting yourself, showing areas with poor blood flow or damage in your heart.
The test usually involves injecting radioactive dye, then taking two sets of images of your heart — one while you're at rest and another after exertion.
A nuclear stress test is one of several types of stress tests that may be performed alone or in combination. Compared with an exercise stress test, a nuclear stress test can help better determine your risk of a heart attack or other cardiac event if your doctor knows or suspects that you have coronary artery disease.
You may need a nuclear stress test if a routine stress test didn't pinpoint the cause of symptoms such as chest pain or shortness of breath. A nuclear stress test may also be used to guide your treatment if you've been diagnosed with a heart condition. Your doctor may recommend a nuclear stress test to:
Diagnose coronary artery disease. Your coronary arteries are the major blood vessels that supply your heart with blood, oxygen and nutrients. Coronary artery disease develops when these arteries become damaged or diseased — usually due to a buildup of deposits containing cholesterol and other substances (plaques).
If you have symptoms such as chest pain or shortness of breath, a nuclear stress test can help determine if you have coronary artery disease and how severe the condition is.
- Guide treatment of heart disorders. If you've been diagnosed with coronary artery disease, a nuclear stress test can help your doctor find out how well treatment is working. It may also be used to help establish the right treatment plan for you by determining how much exercise your heart can handle.
A nuclear stress test is generally safe, and complications are rare. As with any medical procedure, there is a risk of complications, including:
- Allergic reaction. Though rare, you could be allergic to the radioactive dye that's injected during a nuclear stress test.
- Abnormal heart rhythms (arrhythmias). Arrhythmias brought on during a stress test usually go away shortly after you stop exercising or the medication wears off. Life-threatening arrhythmias are rare.
- Heart attack (myocardial infarction). Although extremely rare, it's possible that a nuclear stress test could cause a heart attack.
- Dizziness or chest pain. These symptoms can occur during a stress test. Other possible signs and symptoms include nausea, shakiness, headache, flushing, shortness of breath and anxiety. These signs and symptoms are usually mild and brief, but tell your doctor if they occur.
- Low blood pressure. Blood pressure may drop during or immediately after exercise, possibly causing you to feel dizzy or faint. The problem should go away after you stop exercising.
Your doctor will give you specific instructions on how to prepare for your nuclear stress test.
Food and medications
You may be asked not to eat, drink or smoke for a period of time before a nuclear stress test. You may need to avoid caffeine the day before and the day of the test.
Ask your doctor if it's safe for you to continue taking all of your prescription and over-the-counter medications before the test, because they might interfere with certain stress tests.
If you use an inhaler for asthma or other breathing problems, bring it to the test. Make sure your doctor and the health care team member monitoring your stress test know that you use an inhaler.
Clothing and personal items
Wear or bring comfortable clothes and walking shoes. Don't apply oil, lotion or cream to your skin on the day of your nuclear stress test.
A nuclear stress test may be performed in combination with an exercise stress test, in which you walk on a treadmill. If you aren't able to exercise, you'll receive a drug through an IV that mimics exercise by increasing blood flow to your heart. A nuclear stress test can take two or more hours, depending on the radioactive material and imaging tests used.
Before a nuclear stress test
First, your doctor will ask you some questions about your medical history and how often and strenuously you exercise. This helps determine the amount of exercise that's appropriate for you during the test. Your doctor will also listen to your heart and lungs for any abnormalities that might affect your test results.
During a nuclear stress test
Before you start the test, a technician inserts an intravenous (IV) line into your arm and injects a radioactive dye (radiopharmaceutical or radiotracer).
The radiotracer may feel cold when it's first injected into your arm. It takes about 20 to 40 minutes for your heart cells to absorb the radiotracer. Then, you'll lie still on a table and have your first set of images taken while your heart is at rest.
A nurse or technician will place sticky patches (electrodes) on your chest, legs and arms. Some areas may need to be shaved to help them stick. The electrodes have wires connected to an electrocardiogram machine, which records the electrical signals that trigger your heartbeats. A cuff on your arm checks your blood pressure during the test. You may be asked to breathe into a tube during the test to show how well you're able to breathe during exercise.
If you can't exercise, your doctor will inject the drug into your IV line that mimics exercise by increasing blood flow to your heart. Possible side effects may be similar to those caused by exercise, such as flushing or shortness of breath. You might get a headache.
For an exercise stress test, you'll probably walk on a treadmill or ride a stationary bike. You'll start slowly, and the exercise gets more difficult as the test progresses. You can use the railing on the treadmill for balance. Don't hang on tightly, as this may skew the results.
You'll continue exercising until either your heart rate has reached a set target, you develop symptoms that don't allow you to continue or you develop:
- Moderate to severe chest pain
- Severe shortness of breath
- Abnormally high or low blood pressure
- An abnormal heart rhythm
- Certain changes in your electrocardiogram
You and your doctor will discuss your safe limits for exercise. You can stop the test anytime you're too uncomfortable to continue.
You'll have another injection of radiotracer when your heart rate peaks. About 20 to 40 minutes later, you'll lie still on a table and have a second set of images made of your heart muscle. The dye shows any areas of your heart receiving inadequate blood flow.
Your doctor will use the two sets of images to compare the blood flow through your heart while you're at rest and under stress.
After a nuclear stress test
After you stop exercising, you might be asked to stand still for several seconds and then lie down for a period of time with the monitors in place. Your doctor can watch for any abnormalities as your heart rate and breathing return to normal.
When the test is complete, you may return to normal activities unless your doctor tells you otherwise. The radioactive material will naturally leave your body in your urine or stool. Drink plenty of water to help flush the dye out of your system.
Your doctor will discuss your nuclear stress test results with you. Your results could show:
- Normal blood flow during exercise and rest. You may not need further tests.
- Normal blood flow during rest, but not during exercise. Part of your heart isn't receiving enough blood when you're exerting yourself. This might mean that you have one or more blocked arteries (coronary artery disease).
- Low blood flow during rest and exercise. Part of your heart isn't getting enough blood at all times, which could be due to severe coronary artery disease or a previous heart attack.
- Lack of radioactive dye in parts of your heart. Areas of your heart that don't show the radioactive dye have tissue damage from a heart attack.
If you don't have enough blood flow through your heart, you may need to undergo coronary angiography. This test looks directly at the blood vessels supplying your heart. If you have severe blockages, you may need a coronary intervention (angioplasty and stent placement) or open-heart surgery (coronary artery bypass).