(Exercise Thallium, Stress Thallium, Cardiac Nuclear Imaging, Adenosine Thallium Scan, Cardiolite Scan)
A myocardial perfusion scan is a type of nuclear medicine procedure. This means that a tiny amount of a radioactive substance, called a radionuclide (radiopharmaceutical or radioactive tracer), is used during the procedure to assist in the examination of the tissue under study. Specifically, the myocardial perfusion scan evaluates the heart’s function and blood flow.
A radionuclide is a radioactive substance used as a "tracer," which means it travels through the blood stream and is taken up (absorbed) by the healthy heart muscle tissue. On the scan, the areas where the radionuclide has been absorbed will show up differently than the areas that do not absorb it (due to possible damage to the tissue from decreased or blocked blood flow).
A stress myocardial perfusion scan is used to assess the blood flow to the heart muscle (myocardium) when it is stressed by exercise or medication and to determine what areas of the myocardium have decreased blood flow. This is done by injecting a radionuclide (thallium or technetium) into a vein in the arm or hand.
There are different types of radionuclides. When one type of radionuclide is used, areas of the myocardium that have blocked or partially blocked arteries will be seen on the scan as "cold spots," or "defects," because these areas will be unable to take in the radionuclide into the myocardium. Another type of radionuclide binds to the calcium that is released when a heart attack occurs, so it will accumulate in area(s) of injured heart tissue as a “hot spot” on the scan.
There are two types of stress myocardial perfusion scans, one that is used in conjunction with exercise (myocardial perfusion scan with exercise) and one that is used in conjunction with medication (pharmacologic myocardial perfusion scan).
Other related procedures that may be used to diagnose heart disorders include exercise and resting electrocardiograms (ECG or EKG), Holter monitor, signal-averaged ECG, cardiac catheterization, chest X-ray, computed tomography (CT scan) of the chest, echocardiography, electrophysiological studies, magnetic resonance imaging (MRI) of the heart, radionuclide angiography, and cardiac CT scan. Please see these procedures for additional information.
Coronary artery disease (CAD) is the narrowing of the coronary arteries (the blood vessels that supply oxygen and nutrients to the heart muscle), caused by a buildup of fatty material within the walls of the arteries. This process causes the inside of the arteries to become rough and narrowed, limiting the supply of oxygen-rich blood to the heart muscle.
To better understand how coronary artery disease affects the heart, a review of basic heart anatomy and function follows.
The heart is basically a pump. The heart is made up of specialized muscle tissue, called the myocardium. The heart's primary function is to pump blood throughout the body, so that the body's tissues can receive oxygen and nutrients and have waste substances taken away.
Like any pump, the heart requires fuel in order to work. The myocardium requires oxygen and nutrients, just like any other tissue in the body. However, the blood that passes through the heart's chambers is only passing through on its trip to the rest of the body. This blood does not give oxygen and nutrients to the myocardium. The myocardium receives its oxygen and nutrients from the coronary arteries, which lie on the outside of the heart.
When the heart tissue does not receive an adequate blood supply, it cannot function as well as it should. If the myocardium's blood supply is decreased for a length of time, a condition called ischemia may develop. Ischemia can decrease the heart's pumping ability, because the heart muscle becomes weakened due to a lack of oxygen.
Fortunately, the technology is available to restore blood flow to heart tissue when coronary artery blockages are diagnosed. One of several procedures used to diagnose and evaluate coronary artery disease is the myocardial perfusion scan.
Indications for an exercise or pharmacologic myocardial perfusion scan may include, but are not limited to, the following:
There may be other reasons for your doctor to recommend a myocardial perfusion scan.
The exercise portion of the test may lead to rare instances of abnormal heart rhythms, chest pain, or heart attack due to the stress on the heart caused by the exercise.
The injection of the radionuclide may cause some slight discomfort. Allergic reactions to the radionuclide are rare.
If you are pregnant or suspect that you may be pregnant, you should notify your health care provider due to the risk of injury to the fetus from a myocardial perfusion scan. Radiation exposure during pregnancy may lead to birth defects. If you are lactating, or breastfeeding, you should notify your health care provider due to the risk of contaminating breast milk with the radionuclide.
Patients who are allergic to or sensitive to medications, contrast dyes, iodine, tape, or latex should notify their doctor.
There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.
Certain factors or conditions may interfere with or affect the results of the test. These include, but are not limited to, the following:
A stress myocardial perfusion scan may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.
Generally, a stress myocardial perfusion scan follows this process:
You should move slowly when getting up from the scanner table to avoid any dizziness or lightheadedness from lying flat for the length of the procedure.
You will be instructed to drink plenty of fluids and empty your bladder frequently for 24 to 48 hours after the test to help flush the remaining radionuclide from your body.
The IV site will be checked for any signs of redness or swelling. If you notice any pain, redness, and/or swelling at the IV site after you return home following your procedure, you should notify your doctor as this may indicate an infection or other type of reaction.
Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.
The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.
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