What is a nuclear stress test

A nuclear stress test provides images of the blood flow to the heart muscle both under resting conditions and during stress (this can be accomplished with either exercise or medications). The nuclear heart stress test usually involves injecting radioactive dye (such as thallium or sestamibi), then taking two sets of images of your heart — one while you’re at rest and another after exertion. A nuclear stress test can be used to detect abnormal blood flow to the heart muscle from blockages or narrowing in the coronary arteries and the presence of prior heart attacks. The nuclear stress test can show the size of your heart’s chambers, how well your heart is pumping blood, and whether your heart has any damaged or dead muscle. Nuclear stress tests can also give doctors information about your arteries and whether they might be narrowed or blocked because of coronary artery disease. However, nuclear stress test will not identify the presence of plaques that do not limit blood flow in your coronary arteries ¹.

A nuclear stress test is almost the same as the exercise stress test, except doctors will give you a small amount of a radioactive substance just before the end of the exercise part of the test. 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 radioactive substance is not harmful to your body or your organs.

Certain factors may interfere with or affect the results of nuclear stress test. These include:

• Use of medicines containing theophylline
• Caffeine intake within 48 hours of the procedure
• Smoking or using any form of tobacco within 48 hours of the procedure
• Certain heart medicines, such as those that slow the heart rate

There are 2 types of nuclear stress tests. The most commonly available test is single-photon emission computed tomography (SPECT), although some centers may use positron emission tomography (PET). Positron emission tomography (PET) has limited availability but may provide improved images, particularly in obese patients.

Nuclear stress test techniques:

1. Thallium-201 SPECT
   • excessive radiation dose (c.f. 99mTc-MIBI)
   • redistribution may occur
   • single injection for stress and resting phase
2. 99mTc-Sestamibi SPECT
   • less radiation dose
   • no redistribution
   • separate injections for stress and resting phase
3. FDG-PET (for viability)
   • based on the fact that myocardium (heart muscle) utilizes glucose for metabolism when under effect of ischemia (hence the ischemic myocardium will show greater uptake than normal cells)
   • under normal circumstances, it utilizes fatty acids for energy
   • non-viable myocardium will not show any uptake

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.

Nuclear heart scans are used for three main purposes:

1. To check how blood is flowing to the heart muscle. If part of the heart muscle isn’t getting blood, it may be a sign of coronary heart disease (coronary artery disease). Coronary artery disease can lead to chest pain called angina, a heart attack, and other heart problems. When a nuclear stress test is done for this purpose, it’s called myocardial perfusion scanning.
2. To look for damaged heart muscle. Damage might be the result of a previous heart attack, injury, infection, or medicine. When a nuclear stress test is done for this purpose, it’s called myocardial viability testing.
3. To see how well your heart pumps blood to your body. When a nuclear stress test is done for this purpose, it’s called ventricular function scanning.

Usually, two sets of pictures are taken during a nuclear cardiac stress test. The first set is taken right after a stress test, while your heart is beating fast.

• During a nuclear cardiac stress test, you exercise to make your heart work hard and beat fast. If you can’t exercise, you might be given medicine to increase your heart rate. This is called a pharmacological stress test.
• The second set of pictures is taken later, while your heart is at rest and beating at a normal rate..

The results of the nuclear stress test can show doctors if the heart is not working properly while you are resting, exercising, or both. If the nuclear stress test shows that blood flow is normal while you are resting but not normal while you are exercising, then doctors know that your blood flow to your heart is not adequate during times of stress. The heart normally pumps more blood during times of physical exertion. If the nuclear stress test results are not normal during both parts of the test (rest and exercise), part of your heart is permanently deprived of blood or is scarred. If doctors cannot see the radioactive substance in one part of your heart, it probably means that section of heart muscle has died, either because of a previous heart attack or because the coronary arteries supplying blood to that area of the heart are blocked.

Just like the exercise stress test, you will have small metal disks called electrodes placed on your chest and back. The electrodes are attached to wires called leads, which are attached to an electrocardiogram machine. Doctors will then have you walk on a treadmill.

After your doctors have the information they need from the exercise part of the test, you will step off of the treadmill and go into another room. You will be given an injection of a radioactive substance (either thallium or sestamibi), and you will be asked to lie on an examination table, which has a gamma-ray camera above it. The camera is used to take pictures of your heart. The camera can pick up traces of the radioactive substance in your body and then send a picture to a television monitor.

After this part of the test is over, you can leave the testing area for 3 or 4 hours. Doctors will ask you not to exercise or drink or eat anything with caffeine, such as coffee, tea, sodas, or chocolate. When you return, doctors will give you another injection of the radioactive substance. You will be asked to lie down on the examination table, and the gamma-ray camera will take pictures of your heart while you are resting. This will give your doctor an idea of how your heart works during both exercise and rest.

After the test is over, you may eat, drink, and go back to your normal activities right away.

Does a nuclear stress test show blocked arteries?

Yes. Because the radioactive tracer highlights areas of blood flow, nuclear stress test SPECT (single-photon emission computed tomography) can check for:

• Clogged coronary arteries. If the arteries that feed the heart muscle become narrowed or clogged, the portions of the heart muscle served by these arteries can become damaged or even die.
• Reduced pumping efficiency. Nuclear stress test SPECT can show how completely your heart chambers empty during contractions.

In some cases, other organs and structures can cause false positive results. However, special steps can be taken to avoid this problem.

You may need additional tests, such as cardiac catheterization, depending on your test results.

Is there anyone that a nuclear heart stress test wouldn’t be suitable for?

Nuclear stress test is NOT recommended for:

• Patients with severe obesity because the test may have limited images
• If you are pregnant or breastfeeding due to risk of radiation from the radioactive materials. If you are breastfeeding, you should notify your health care provider due to the risk of contaminating breast milk with the tracer.

Women should always inform their physician or technologist if there is any possibility that they are pregnant or if they are breastfeeding.

If your doctor know that you have a severe cardiac problem then he/she wouldn’t always consider a stress test, but it is suitable for most people.

How long does a nuclear stress test take?

A nuclear stress test can take two or more hours, depending on the radioactive material and imaging tests used.

Reasons for performing a nuclear stress test

The nuclear stress test is done to see if your heart muscle is getting enough blood flow and oxygen when it is working hard (under stress).

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 provider may order nuclear stress test to find out:

• How well a treatment (medicines, angioplasty, or heart surgery) is working
• If you are at high risk for heart disease or complications
• If you are planning to start an exercise program or have surgery
• The cause of new chest pain or worsening angina
• What you can expect after you have had a heart attack
• Unexplained chest pain.
• Chest pain brought on by exercise (called angina).
• Shortness of breath with exertion.
• Abnormal electrocardiogram.

Cardiac nuclear medicine imaging is also performed:

• to visualize blood flow patterns to the heart walls, called a myocardial perfusion scan.
• to evaluate the presence and extent of suspected or known coronary artery disease.
• to determine the extent of injury to the heart following a heart attack, or myocardial infarction.
• to evaluate the results of bypass surgery or other revascularization procedures designed to restore blood supply to the heart.
• in conjunction with an electrocardiogram (ECG), to evaluate heart-wall movement and overall heart function with a technique called cardiac gating.

The results of a nuclear stress test can help:

• Determine how well your heart is pumping
• Determine the proper treatment for coronary heart disease
• Diagnose coronary artery disease
• See whether your heart is too large

A normal nuclear stress test most often means that you were able to exercise as long as or longer than most people of your age and gender. You also did not have symptoms or changes in blood pressure, your ECG or the images of your heart that caused concern.

A normal result means blood flow through the coronary arteries is probably normal.

The meaning of your test results depends on the reason for the test, your age, and your history of heart and other medical problems.

Nuclear stress test prep

Your doctor will give you specific instructions on how to prepare for your nuclear stress test.

Women should always inform their physician or technologist if there is any possibility that they are pregnant or if they are breastfeeding.

You should inform your physician and the technologist performing your exam of any medications you are taking, including vitamins and herbal supplements. You should also inform them if you have any allergies and about recent illnesses or other medical conditions.

You should inform your physician if you are pregnant or breastfeeding and/or if you have:

• had a recent heart attack or myocardial infarction
• heart failure
• asthma
• chronic lung disease
• conduction abnormalities within the heart (such as AV block), aortic stenosis or other abnormalities with the valves of your heart
• any abnormality with the heart and lungs

Also, if you have problems with your knees, hips or keeping your balance, tell your doctor as this may limit your ability to perform the exercise needed for this procedure. You should wear comfortable clothing and walking shoes. Do not apply oil, lotion, or cream to your skin the day of the exam. If you use an inhaler for asthma or other breathing problems, bring it to the test and make sure the health care team monitoring your stress test knows that you use an inhaler.

Jewelry and other metallic accessories should be left at home if possible, or removed prior to the exam because they may interfere with the procedure.

You should wear comfortable clothes and shoes with non-skid soles. You may be asked not to eat or drink after midnight. You will be allowed to have a few sips of water if you need to take medicines.

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.

You will need to AVOID caffeine for 24 hours before the nuclear stress test. This includes:

• Tea and coffee
• All sodas, even ones that are labeled caffeine-free
• Chocolates, and certain pain relievers that contain caffeine

Many medicines can interfere with blood test results.

• Your provider will tell you if you need to stop taking any medicines before you have this test.
• DO NOT stop or change your medicines without talking to your doctor first.

Nuclear stress test procedure

Nuclear stress test is done at a medical center or health care provider’s office. Nuclear stress test is done in stages:

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.

You will have an intravenous (IV) line started.

• Before you start the test, a technician inserts an intravenous (IV) line into your arm and injects a radioactive dye (radiopharmaceutical or radiotracer), such as thallium or sestamibi, will be injected into one of your veins.
• 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.
• You will lie down and wait for between 15 and 45 minutes.
• A special camera will scan your heart and create pictures to show how the substance has traveled through your blood and into your heart.

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.

Most people will then walk on a treadmill (or pedal on an exercise machine).

• 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.
• After the treadmill starts moving slowly, you will be asked to walk (or pedal ride a stationary bike) faster and on an incline.
• 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
  • Dizziness
  • 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.
• If you are not able to exercise, you may be given a medicine called a vasodilator. This drug widens (dilates) your heart arteries. Possible side effects may be similar to those caused by exercise, such as flushing or shortness of breath. You might get a headache.
• In other cases, you may get a medicine (dobutamine) that will make your heart beat faster and harder, similar to when you exercise.

Your blood pressure and heart rhythm (ECG) will be watched throughout the test.

When your heart is working as hard as it can, a radioactive substance is again injected into one of your veins.

• You will wait for 15 to 45 minutes.
• Again, the special camera will scan your heart and create pictures. 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.
• You may be allowed to get up from the table or chair and have a snack or drink.

Your provider will compare the 1st (at rest) and 2nd set (during exercise or under stress) of pictures using a computer. This can help detect if you have heart disease or if your heart disease is becoming worse.

During the nuclear stress test, some people feel:

• Chest pain
• Fatigue
• Muscle cramps in the legs or feet
• Shortness of breath

If you are given the vasodilator drug, you may feel a sting as the medicine is injected. This is followed by a feeling of warmth. Some people also have a headache, nausea, and a feeling that their heart is racing.

If you are given medicine to make your heart beat stronger and faster (dobutamine), you may have a headache, nausea, or your heart may pound faster and more strongly.

Rarely, during the nuclear stress test people experience:

• Chest discomfort
• Dizziness
• Palpitations
• Shortness of breath

If any of these symptoms occur during your nuclear stress test, tell the person performing the test right away.

Precautions after 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.

Through the natural process of radioactive decay, the small amount of radiotracer in your body will lose its radioactivity over time. It may also pass out of your body through your urine or stool during the first few hours or days following the test. You should also drink plenty of water for 24 to 48 hours to help flush the radioactive material out of your body as instructed by the nuclear medicine personnel.

Your healthcare provider may give your other instructions after the procedure, depending on your particular situation.

Abnormal nuclear stress test results

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.

Abnormal nuclear stress test results may be due to:

• Reduced blood flow to a part of the heart. The most likely cause is a narrowing or blockage of one or more of the arteries that supply your heart muscle.
• Scarring of the heart muscle due to a previous heart attack.

In some cases, other organs and structures can cause false positive results. However, special steps can be taken to avoid this problem.

You may need additional tests, such as cardiac catheterization, depending on your test results.

After the nuclear stress test you may need:

• Angioplasty and stent placement
• Changes in your heart medicines
• Coronary angiography
• Heart bypass surgery

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).

Nuclear stress test side effects

A nuclear stress test is generally safe, and complications are rare. Your symptoms will be carefully monitored and the person doing the nuclear stress test will know that they need to stop if any symptoms occur. There is no significant risk from the nuclear stress test, as it will be performed under controlled and monitored conditions. The nuclear stress test would be stopped well before you get to a level of exercise that would cause the heart to struggle.

It’s much safer to do a controlled nuclear stress test like this than to run 10km knowing that there might be something wrong with the heart.

Women should always inform their physician or radiology technologist if there is any possibility that they are pregnant or if they are breastfeeding.

Complications of nuclear stress test are rare, but may include:

• 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.
• Increased angina pain during the test
• Breathing problems or asthma-like reactions
• Extreme swings in blood pressure
• Skin rashes
• 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 provider will explain the risks before the nuclear stress test.

Nuclear stress test risks

The majority of cardiac imaging tests are extremely safe. During tests that use exercise or medications that simulate the effects of exercise, the chance of having a heart attack or dying as a result of the test is less than 1 in 10,000 ¹.

Table 1. Typical Radiation Exposure Associated With Cardiac Imaging Tests Relative to Naturally Occurring Background Radiation Exposure

Test Type	Exposure (Relative to Row 1)
Naturally occurring annual background radiation exposure for a person living in the United States (≈3 mSv)	1
Coronary artery calcium score	0.5
Cardiac computed tomography angiography	1–4
Nuclear stress test (single-photon emission computed tomography)	3–4
Exercise treadmill testing (with no imaging)	0
Cardiac magnetic resonance imaging/echocardiogram	0

[Sources ², ¹]

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2. Fazel R, Dilsizian V, Einstein AJ, Ficaro EP, Henzlova M, Shaw LJ. Strategies for defining an optimal risk-benefit ratio for stress myocardial perfusion spect. J Nucl Cardiol. 2011;18:385–392.[↩]