Nuclear Stress Tests: Uses, Risks, and Understanding Results

A nuclear stress test is an imaging test that requires you to be injected with a small radioactive tracer that helps doctors determine how well your heart is functioning. The tracer will lose its radioactivity through natural decay in about a day or two.

Also known simply as a stress test, a nuclear stress test can show how well your heart is pumping and how well blood is flowing through it while you exercise on a treadmill or stationary bike. Depending on the imaging technology used, the nuclear stress test may be referred to as cardiac positron emission tomography (PET), cardiac single photo emission computed tomography (SPECT), or myocardial perfusion imaging (MPI).

This article discusses the purpose, types, and potential risks of a nuclear stress test. It will also help you prepare by knowing what to expect before, during, and after the procedure.

Purpose of a Nuclear Stress Test

A nuclear stress test helps your healthcare provider visualize what is happening in your heart when you exercise. A nuclear stress test is different than a regular stress test. A regular stress test uses an ECG to record your heart rate and rhythm, while a nuclear stress test captures images of your heart.

The nuclear stress test uses a radioactive tracer to make a picture. The tracer is a very small amount of radioactive material that is delivered into your body through an intravenous (IV) line. 

What the Test Is Looking For

The nuclear stress test creates two images. The first shows how blood flows to your heart when you are resting. The second shows the blood flow during exercise.

The test can show:

• The presence, location, and size of a prior heart attack
• The presence, location, and size of blockages that are serious enough to affect blood flow during exercise

The images can tell your provider different things about your heart health:

• A normal test result will show blood being evenly distributed to the heart in both images.
• If both images show a fixed patch of poor blood flow, that means the person had a heart attack at some point.
• If an area of poor blood flow is seen on the exercise image, but not on the rest image, it means there is probably a blockage in one of the coronary arteries. The blockage is causing a temporary drop in blood flow.

Who Needs a Nuclear Stress Test

A nuclear stress test is an important tool for diagnosing or monitoring heart problems like coronary artery disease (CAD) or congestive heart failure (CHF).

Your provider may order a nuclear stress test if you have certain symptoms of CAD, such as:

• Chest pain
• Shortness of breath (dyspnea)

The test can also find blockages and help your provider judge how bad they are.

If you already have been diagnosed with CAD, your provider might want you to have the test because the results can help them come up with a treatment plan for you.

If you are being treated for CAD, the test can help your provider understand how well your treatment is working. It will also help your provider decide what kinds of daily activities and exercise you should be doing.

The nuclear stress test does not involve inserting medical instruments into your body. This means it is non-invasive. The test is thought to be the most accurate and non-invasive way to diagnose coronary artery blockages.

CAD can also be diagnosed with an invasive test called cardiac catheterization—a procedure where a tube called a catheter is inserted into a blood vessel in the heart.

Risks and Contraindications

When performed by experienced providers, the nuclear stress test is very safe. Still, there are known risks.

Radiation Exposure

During a typical nuclear stress test, you are exposed to 11 millisieverts of radiation. This is about three times the dose of radiation that you get just from going about your normal, day-to-day life for one year.

A dose of 11 millisieverts is considered a small amount of radiation exposure. By itself, it should not increase your lifetime risk of cancer by any measurable amount.

The risk of radiation exposure to other people after a nuclear stress test is low. However, some healthcare providers recommend no close contact with children or babies for one to two days after a nuclear stress test. Out of an abundance of caution, you may also want to avoid close contact with pets.

Test-Related Complications

Possible risks of having a nuclear stress test that you should be aware of include:

• Cardiac arrhythmias: Exercise-induced heart arrhythmias occur when your heart beats too fast, too slow, or irregularly. Arrhythmias are usually not dangerous. They almost always go away when the person stops exercising. While arrhythmias are a risk of stress testing, their presence can also help with diagnosis. If you're worried about them, keep in mind that if dangerous arrhythmias happen during modest exercise, the safest way to find out about them is in a controlled setting under the care of a provider.
• Chest pain, dizziness, or other symptoms: In people with serious CAD, modest exercise can cause symptoms of insufficient blood flow to the heart muscle (cardiac ischemia). While it is a risk of the test, it can also be useful for providers to see exercise-related symptoms during the test. In fact, in people who are being assessed for exercise-related symptoms, one of the goals is to reproduce the symptoms during the test.
• Allergic reaction: Some people may have an allergic reaction to the radioactive tracer, but this is very rare.
• Heart attack: It's very rare, but if a person has a critical blockage, exercise might produce a heart attack.

Who Should Not Get the Test?

Some people should not do nuclear stress testing.

If you have the following conditions, your provider may not want you to have the test:

• Uncontrolled heart failure
• Heart attack within the past 2 days
• Unstable angina
• Uncontrolled life-threatening cardiac arrhythmias
• Severe valvular heart disease
• Active endocarditis
• Acute aortic dissection
• A recent pulmonary embolus or deep vein thrombosis

Pharmacologic Stress Testing

People with physical limitations that make exercise difficult or impossible can have pharmacologic stress testing instead of exercise stress testing. This is done with drugs that cause the same stress on the heart as exercise.

The types of drugs used may include:

• Vasodilators such as Adenocard (adenosine) or Persantine (dipyridamole)
• Inotropic drugs, usually Dobutrex (dobutamine)

Vasodilators are usually preferred for the pharmacologic stress test. These are medications that dilate or open the blood vessels. Your provider will choose the best drug for your case if exercise is not an option.

Before the Test

It is normal to have some anxiety about having a nuclear stress test. Knowing how to prepare and what to expect may help relieve your nerves.

Timing and Location

Most nuclear stress tests are performed in a hospital outpatient department.

You will probably be asked to show up at least 30 minutes before the scheduled test. You can expect to be at the hospital for at least four hours.

What to Wear

Since you will be exercising, bring comfortable, loose-fitting clothing and shoes that fit well. Many people bring gym clothes and walking or running shoes.

Most testing facilities will provide a place for you to change your clothes.

Food and Drink

You will be asked to not have any food or drink four to six hours before your test. You will also be asked not to smoke for four to six hours before you arrive.

You will also need to avoid caffeine for at least 24 hours before the test.

Medications

It's important that you tell your provider about all the medications you take, even over-the-counter ones. Ask your provider which medications you should take on the day of testing, and which you should not take.

For instance, your provider may tell you not to take beta-blockers, nitroglycerin, or heart medications for 24 hours before the test. You may also need to stop aspirin, blood thinners, and asthma medications 48 hours before the test.

If you have diabetes, you'll be given instructions on how to take your medications on the day of the test.

Avoid taking any over-the-counter (OTC) medications before the test unless your provider says that it's OK to take them.

Cost and Health Insurance

A nuclear stress test can be expensive, but the cost varies from facility to facility. If you have health insurance, the cost will also depend on your coverage.

Most medical insurance will cover a nuclear stress test if a qualified cardiologist says that you need it. To be sure, check with your insurance company before you have the test.

What to Bring

You will probably have a few hours of downtime during the test. You may want to bring a book or have a game to play on your phone to pass the time.

Other Considerations

If possible, bring a family member or a friend with you on the day of the test. This person can keep you company and offer support if you expect to get the results.

Pre-Test

After you arrive for testing, you will be interviewed by someone on your healthcare team.

This person will ask if your symptoms or medical condition have changed since you last saw your provider. You will also have a quick physical exam.

Your team will let you know what to expect during the test. You will also be given a chance to ask questions.

During the Test

If you're feeling nervous about the test itself, knowing what will happen during it can make it less overwhelming.

The testing will be overseen by a healthcare provider. They will tell you who they are and what they do before you start the test.

Most labs do one-day nuclear stress testing but it can also be done over two days. One-day testing is generally more convenient for patients.

If you are doing a one-day test, a resting image is captured first. The exercise part will be done later the same day. For a two-day test, the exercise part is usually done on the first day. The resting part is done on the second day.

During the resting test, a technician will put an IV line into one of your veins so the tracer can be injected. This image only needs a small dose of Tc-99. It is captured with a special camera that is used to scan the chest (gamma camera).

After about 20 minutes, you will lie down under the gamma camera. You will need to keep your arms above your head and lie still. It will take another 15 to 20 minutes to make the image. The image will show how the blood is flowing to your heart.

Before the exercise test, a technician will put electrodes on your chest. The electrodes allow an electrocardiogram (ECG) to be recorded while you are exercising. This test measures the electrical rhythm of your heart. 

When the test starts, you will walk on a treadmill or pedal a stationary bike at a very slow pace. The level of exercise will increase every three minutes. The exercise will stop when one of these things happens:

• You become fatigued.
• You start having symptoms.
• You reach your target heart rate.

Your ECG and vital signs will be monitored throughout the exercise and recovery periods. The exercise itself usually lasts for no more than six to 12 minutes.

When you have reached the maximum level of exercise, the tracer will be injected into your IV. At that point, you will stop exercising. For the exercise image, the Tc-99 dose is much larger than it was for the resting image.

Twenty to 30 minutes after you've finished exercising, you will lie under the gamma camera again. You will be asked to keep your arms above your head. The exercise cardiac image takes about 20 minutes to make.

After the Test

Most people can go back to their normal routine immediately after the test. This includes having meals, taking medications, and doing other activities.

How and when you get your results depends on the testing center. Most laboratories will give you an overview of the results right away. If the test finds problems, you'll be given advice on what to do next.

If there are no obvious problems, you likely will not get the formal results of the test until a cardiologist looks at the images.

In this case, you'll get your results from the provider who ordered the test. From there, you'll discuss what, if anything, should be done next.

Managing Side Effects

Most people don't experience any significant side effects from a nuclear stress test. When they do occur, side effects may include:

• Headache (may be related to fasting or exercise intensity)
• Nausea (tracer may cause this side effect in some people)
• Soreness at the injection site
• Fatigue from the exercise

More serious side effects are uncommon. If you have any unusual symptoms after the test, call your provider.

Interpreting the Results of a Nuclear Stress Test

The interpretation of the results is different for everyone. You'll need to discuss the results with your provider.

In general, the results of a nuclear stress test fall into three categories.

1. Both the resting and exercise cardiac images are normal

If both your resting and exercise images were normal, it means that:

• There is no detectable permanent heart damage from a prior heart attack.
• No part of the heart is deprived of blood flow during exercise.

Getting this result strongly suggests that there are no significant coronary artery blockages. In this case, the chance of having CAD is low.

Your healthcare provider will discuss the next steps with you. If your test is normal, you may not need more cardiac testing.

However, if your test was normal but there is strong evidence of CAD, your provider will likely recommend immediate medical treatment. The goal will be to relieve symptoms and slow the progression of the disease.

You may also need to have a different test. For example, your provider may want you to have cardiac catheterization if:

• Your symptoms are very bad.
• Your risk of having an early heart attack is high.
  

2. The resting cardiac image is abnormal

The resting cardiac scan may show an area where blood is not flowing normally to part of the heart.

If you get this result, it indicates that you've had a prior heart attack that caused permanent heart muscle damage.

3. The exercise cardiac scan is abnormal, but the resting image is normal

Getting this result suggests that there is a significant blockage in a coronary artery:

• The heart is getting normal flow at rest.
• The heart is not getting the right amount of blood flow during exercise.

Different parts of the heart muscle may display any of these general findings.

For example, a person could have a “permanent” defect in one part of the heart muscle. This indicates a heart attack has occurred.

They may also have a “reversible” defect in another part of the heart muscle. This indicates there is a blockage but no permanent damage.

Summary

A nuclear stress test is used to find heart problems. The test uses a small amount of radioactive material to record blood flow to your heart. The test is done while you are at rest and exercising.

The nuclear stress test is generally very safe. There are some risks, like cardiac arrhythmias, chest pain, and, in rare cases, heart attack. The amount of radiation used is very small and does not increase your lifetime risk of cancer.

The results of the test can show if you have coronary artery disease, blockages, or a previous heart attack. Your provider will discuss the next steps with you, depending on the results.