What is a nuclear stress test?

Date: Sep-02-2013A nuclear stress test is similar to the exercise stress test or pharmacological (chemical) stress test, but a small amount of radioactive substance is used to determine the health of the heart and blood flow to the heart.

The nuclear stress test can be referred to by other names, such as a thallium stress test1, myocardial perfusion scan2, or radionuclide test3.

The nuclear stress test can be done while the patient is resting or doing exercise. The radioactive substance that is injected into the patient is called a radionuclide

According to the British Heart Foundation, "Radionuclide tests are considered safe4. However, during the test you will be exposed to some radiation."
How can a nuclear test help the doctor?

When a doctor is diagnosing a patient's heart, or determining whether certain treatments are effective, some tests need to be carried out. The nuclear test can give the doctor vital information regarding:

the size of the chambers in the heart
how well the heart is pumping blood
the heart itself, whether any of it, for example muscle, is damaged
the health of arteries that provide blood to the heart (coronary arteries), whether they have narrowed or are blocked due to coronary artery disease
how effective a current treatment has been (heart surgery, angioplasty, medications, etc.)
what to expect after having a heart attack

The test may also help the doctor determine whether the patient is suitable for a cardiac rehabilitation program, and if so, how hard he/she should exercise.

According to the Mercy Medical Center5, a nuclear stress test lasts about three hours.

The coronary arteries (in red) supply the heart muscles with blood. The nuclear stress test can help determine whether they are blocked.

Nuclear stress test with exercise

In this test, the aim is to find out whether any areas of the heart muscle are not receiving enough blood flow during exercise.

A radionuclide, such as thallium or technetium, is injected into a vein in the hand or arm. When the radionuclide has circulated through the blood stream, a gamma camera takes pictures of the heart while the patient is lying down. This is known as the "rest scan" of the heart.

The patient then gets up and goes onto a treadmill. The treadmill starts off slowly and gradually picks up speed and incline so that the patient feels he is walking (or running) uphill.

At peak exercise more radionuclide is injected into the patient. When the radionuclide has passed through the blood stream, the gamma camera takes more pictures of the heart. This is known as the "stress scan" of the heart.

The radionuclide helps blocked or partially blocked arteries show up on the scans, because they do not absorb the radionuclide into the heart - they are known as "cold spots".
Chemical (pharmacological) nuclear stress test without exercise

Some patients, such as those with severe arthritis, are unable to do the physical activity required in a test with exercise. Instead, they are given medications that either speed up the heart rate or dilate the arteries. The body responds in a similar way it would to exercise.

A radionuclide is injected into the patient's arm or hand while he/she is resting. When it has circulated through the bloodstream, a gamma camera takes pictures of the heart - during this process the patient is lying down motionless. As in the test with exercise, this is also known as the "rest scan" of the heart.

The doctor then administers a medication to either speeds up the heart rate or dilates the arteries. When the peak heart rate is reached, the patient is injected again with a radionuclide. As soon as it has circulated throughout the bloodstream the gamma camera takes more pictures. This phase of the procedure is called the "stress scan" of the heart.

As in the stress test with exercise, blocked or partly blocked arteries will show up as "cold spots".
Preparing for the nuclear stress test

Make sure you wear comfortable clothing suitable for physical activity. Your shoes should be designed for running or jogging and have non-skid soles.

The doctor will ask the patient to fast - no food or drink - for some hours before the test. If you are on oral medications, you can take a few sips of water to help you swallow them (ask your doctor).

Caffeine - the medical team will tell you to avoid all caffeine-containing foods and drinks, including coffee, tea, many sodas, chocolate, as well as some painkillers with caffeine added, for at least 24 hours before the test.

Some medications, such as those for angina or asthma can alter the test results. Your doctor might tell you to stop taking them before the test. It is vital that the physician knows exactly what medications you are taking, and only to stop them if you are told to.

Heart medications - the Cleveland Clinic6 says that the following heart medications should not be taken on the day of the test, unless told otherwise by the doctor:

Dilatrate, Isordil (Isosorbide dinitrate)
Minitran, Nitropatches, Nitrostat (nitroglycerin)
Persantine (dipyridamole) - should not be taken 48 hours before the test
Metoprolol, Metoprolol XL, Atenolol (beta blockers)

Erectile dysfunction drugs - the National Institutes of Health7 says it is important for patients who took medications for erectile dysfunction within 24 hours of the test to tell their doctor, examples include Levitra (vardenafil), Viagra (sildenafil citrate) or Cialis (tadalafil).

Diabetes - patients with diabetes who take insulin will be told how much insulin they should take on the test day, in most cases it will be less than their normal morning dose. A person with diabetes cannot fast for too long, and will probably be advised to have a light meal four hours before the test. Patients with diabetes have to follow their doctor's instructions before and after the test.

The patient will be given a consent form to sign. This gives the medical team permission to carry out the procedure. It is important to read it carefully and ask any questions that raise doubts or concern.

Tell the doctor if you have a defibrillator or pacemaker.
The test results

After the test, the doctor will discuss the results with the patient.

The nuclear stress test may show:

Normal blood flow during rest and exercise - this means heart function appears to be normal at all times. The patient probably does not have coronary artery disease. In most cases, no further tests are required.

Normal blood flow during rest, abnormal during exercise - part of the patient's heart muscle is not getting sufficient blood during physical or strenuous activity. There is a probability of coronary artery disease (blocked arteries).

Poor blood flow both during exercise and rest - the heart is never getting enough blood. The patient might have had a previous heart attack, or has severe coronary artery disease.

Imaging shows "cold spots" - cold spots refers to areas of the heart that do not show the radionuclide (radioactive dye). This happens where there is scar tissue (damaged tissue) from a heart attack.

Patients whose hearts are not getting enough blood flow may need to undergo coronary angiography. A coronary angiography is a test that uses dye and special x rays to show the insides of the coronary arteries.

Patients with severe blockages in their arteries may need balloon angioplasty and stent placement, or a coronary artery bypass.
Video - Nuclear Stress Test

Dr. Manual Morlote, Director Nuclear Cardiology Lab, New York Cardiovascular Associates, talks about the nuclear stress test.

Nuclear Stress Test from PARAMOUNT/MD on Vimeo.

Written by Christian Nordqvist

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