Nuclear Stress Test: A Complete Overview

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A nuclear stress test is a study aimed at measuring whether the blood flow to your heart muscle is normal or abnormal. It determines whether a particular area of your heart muscle isn’t receiving adequate blood flow while exercising. The test is equivalent to the exercise stress test or chemical or pharmacological stress test.

The test is usually performed when the subject is doing exercise or resting. The radioactive substance injected into the subject is known as a radionuclide. 

A nuclear stress test takes between 3 to 4 hours. The patient may be exposed to minor radiation, but according to experts, it is a safe test.

Potential Benefits of a Nuclear Stress Test

The nuclear stress test could help identify a heart condition by providing vital information, including:

  • the size of your heart chambers
  • whether there’s any damage to your heart
  • how well your heart is pumping blood
  • whether there’s any narrowing or blockage of the coronary arteries
  • the efficiency of any current treatments

The nuclear stress test can also identify whether the subject is fitting for a cardiac rehabilitation program. It also helps determine how often they need to exercise.

The Nuclear Stress Test: With Exercise

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When it comes to a nuclear stress test with exercise, a radionuclide, e.g., technetium or thallium, is injected into the vein.

As the radionuclide circulates through the bloodstream, a gamma camera takes photos of the heart. This is called the heart rest scan.

Then, the patient gets on a treadmill, which starts slowly but eventually picks up speed to simulate running or walking uphill.

More radionuclide is inserted into the patient at peak exercise. As the radionuclide passes through the bloodstream, the gamma camera takes a few more photos of the heart, a process that is called the heart stress scan.

The radionuclide identifies blocked arteries on the scans as they don’t absorb the radionuclide directly into the heart. These are called “cold spots.”

The Nuclear Stress Test: Without Exercise

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People with critical arthritis are often unable to perform the physical activity involved in a nuclear stress test with exercise. This is where a chemical nuclear stress test can come in handy.

In this test, the person receives special medications that either increase the heart rate speed or enlarge the arteries. Our body responds in the same manner as it does to exercise.

As the patient is resting, a radionuclide is injected into his or her hand or arm. When it’s circulated through the bloodstream, the gamma camera takes photos of the heart. Just like the previous test, this is also called the heart rest scan.

The physician then gives medication to either increase the heart rate speed or widen the arteries. At peak heart rate, the patient is injected with a radionuclide again.

When it’s circulated through the bloodstream, the gamma camera takes pictures and this phase is called the heart stress scan.

Just like the previous test, blocked arteries will appear as “cold spots.”

The results could be superimposed with those of MRI or CT scans, to provide a more detailed picture.

Potential Side Effects and Complications Include:

  • abnormal heart rhythms
  • allergic reactions to the dye
  • sudden drops in blood pressure after exercise, potentially leading to faintness or dizziness
  • chest pain
  • trembling
  • nausea
  • flushing
  • headache
  • anxiety
  • difficulty in breathing

The FDA warns that two drugs used in such tests, Adenoscan and Lexiscan, can increase the chances of heart issues during the test.

These drugs may cause blood to flow drastically to unobstructed areas, which will leave problem areas with no blood. In rare instances, this may cause a heart attack.

Those with unstable angina or similar cardiac instability aren’t considered suitable for these kinds of drugs.

Concerns have been addressed regarding the radiation levels a patient is exposed to during these tests, and whether this raises the risk of severe diseases like cancer.

In the past few years, the numbers of cancer rates and tests have risen, although it remains unknown whether they’re linked.

The risk may depend on the patient’s gender, age, existing health condition, precautions taken, and the dose used. Doctors are obliged to use nuclear stress tests only when necessary.

Preparation Considerations

On the day of the test, it’s essential to wear clothing best suited to physical activity, e.g., shoes for jogging or running with non-skid soles.

It’s in the patient’s best interest to fast from midnight prior to the test. They shouldn’t take any drinks that contain caffeine, including coffee, tea, sodas, etc. in the past 24 hours before the test. 

Some medications, like those for asthma or angina, may alter the results. The patient needs to ask their doctor if they should stop taking them beforehand.

It’s important for patients to let their physician know exactly what type of medications they’re taking. They should only stop them when told so.

Patients must also inform the doctor should they have a defibrillator or pacemaker.

If the patient had taken any erectile dysfunction drug before the day of the test, they should consult their doctor.

Pregnant women should also inform their doctor about it.

Final Thoughts

Nuclear stress testing is the safest, most effective and noninvasive way of evaluating whether blockages in the coronary arteries are present​ and if such blockages are causing symptoms like chest pain, or have already caused permanent heart muscle damage. It’s been proven to be valuable in terms of identifying coronary artery disease, as well as in supporting its treatment.