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Multiple-Gated Acquisition (MUGA) Scan

Multiple-Gated Acquisition (MUGA) Scan

Definition

The multiple-gated acquisition (MUGA) scan is a non-invasive nuclear test that uses a radioactive isotope called technetium to evaluate the functioning of the heart's ventricles.

Purpose

The MUGA scan is performed to determine if the heart's left and right ventricles are functioning properly and to diagnose abnormalities in the heart wall. It can be ordered in the following patients:

  • With known or suspected coronary artery disease, to diagnose the disease and predict outcomes
  • With lesions in their heart valves
  • Who have recently had a heart attack, to assess damage to heart tissue and predict the likelihood of future cardiac events
  • With congestive heart failure
  • Who have undergone percutaneous transluminal coronary angioplasty, coronary artery bypass graft surgery, or medical therapy, to assess the efficacy of the treatment
  • With low cardiac output after open-heart surgery
  • Who are undergoing chemotherapy.

Precautions

Pregnant women and those who are breastfeeding should not be exposed to technetium.

Description

The MUGA scan measures the heart's function and the flow of blood through it. The strongest chamber in the heart is the left ventricle, which serves as the main pump of blood through the body. The left ventricular is assessed by measuring the amount of blood pumped with each heartbeat (the ejection fraction), ventricle filling, and the blood flow into the pumping chamber. A normal ejection fraction is 50% or more. The heart's ejection fraction is one of the most important measures of its performance. The right ventricle's ability to pump blood to the lungs is also assessed, and any abnormalities in the heart wall are identified. The MUGA scan is the most accurate, non-invasive test available to assess the heart's ventricles.

MUGA is a nuclear heart scan, which means that it involves the use of a radioactive isotope that targets the heart and a radionuclide detector that traces the absorption of the radioactive isotope. The isotope is injected into a vein and absorbed by healthy tissue at a known rate during a certain time period. The radio-nuclide detector, in this case a gamma scintillation camera, picks up the gamma rays emitted by the isotope.

During the MUGA scan, electrodes are placed on the patient's body so that an electrocardiogram (ECG) can be conducted. The imaging equipment and computer are synchronized with the ECG so that images of the heart can be recorded without motion or blur. Then a small amount of a mildly radioactive isotope called technetium Tc99m stannous pyrophosphate, usually called technetium, is injected, usually into an arm vein. While the patient lies motionless on the test table, a gamma scintillation camera follows the movement of the technetium through the blood circulating in the heart. The camera, which looks like an x-ray machine and is suspended above the table, moves back and forth over the patient. It displays multiple images of the heart in motion and records them on a computer for later analysis.

The MUGA scan is usually performed in a hospital's nuclear medicine department, but it can also be performed in an outpatient facility or at the patient's bedside if equipment is available. The scan is done immediately after injection of the technetium and usually takes about 30 minutes to one hour. It is also called multigated graft acquisition, multigated acquisition scan, cardiac blood-pool imaging, and equilibrium radionuclide angiography. Test results can be affected by patient movement during the test, electrocardiogram abnormalities, an irregular heartbeat, or long-acting nitrates.

The MUGA scan can be done with the patient at rest or exercising (called a stress MUGA). The stress MUGA is often performed in patients who have or are suspected of having coronary artery disease. The resting MUGA is compared to the stress MUGA and changes in the heart's pumping performance are analyzed. In some cases, the rest MUGA is compared to a nitroglycerin MUGA, in which a strong heart drug called nitroglycerin is administered to the patient before the scan. For the nitroglycerin MUGA, a cardiologist should be present.

The MUGA scan is not dangerous. The technetium is completely gone from the body within a few days of the test. The scan itself exposes the patient to about the same amount of radiation as a chest x ray. The patient can resume normal activities immediately after the test.

Normal results

If the patient's heart is normal, the technetium will appear to be evenly distributed in the scans. In a stress MUGA, patients with normal hearts will exhibit an increase in ejection fraction or no change.

Abnormal results

An uneven distribution of technetium in the heart indicates that the patient has coronary artery disease, a cardiomyopathy, or blood shunting within the heart. Abnormalities in a resting MUGA usually indicate a heart attack, while those that occur during exercise usually indicate ischemia. In a stress MUGA, patients with coronary artery disease may exhibit a decrease in ejection fraction.

Resources

ORGANIZATIONS

American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. http://www.americanheart.org.

Texas Heart Institute. Heart Information Service. P.O. Box 20345, Houston, TX 77225-0345. http://www.tmc.edu/thi.

KEY TERMS

Ejection fraction The fraction of all blood in the ventricle that is ejected at each heartbeat. One of the main advantages of the MUGA scan is its ability to measure ejection fraction, one of the most important measures of the heart's performance.

Electrocardiogram A test in which electronic sensors called electrodes are placed on the body to record the heart's electrical activities.

Heart attack A cardiac emergency that occurs when a clot blocks blood flow in one or more of the heart's arteries. Oxygen supply to the heart muscle is cut off, resulting in the death of heart tissue in the affected area.

Ischemia A decreased supply of oxygenated blood to a body part or organ, often marked by pain and organ dysfunction, as in ischemic heart disease.

Non-invasive A procedure that does not penetrate the body.

Radioactive isotope One of two or more atoms with the same number of protons but a different number of neutrons with a nuclear composition. In nuclear scanning, radioactive isotopes are used as a diagnostic agent.

Technetium A radioactive isotope frequently used in radionuclide scanning of the heart and other organs. It is produced during nuclear fission reactions.

Ventricles The heart's lower chambers are called the left and right ventricles. They send blood to the lungs and throughout the body. The MUGA scan is performed to evaluate the ventricles.

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Multiple-Gated Acquisition (MUGA) Scan

Multiple-gated acquisition (MUGA) scan

Definition

The multiple-gated acquisition (MUGA) scan, also called a cardiac blood pool study, is a non-invasive nuclear medicine test that enables clinicians to obtain information about heart muscle activity. The scan displays the distribution of a radioactive tracer in the heart. The images of the heart are obtained at intervals throughout the cardiac cycle, and are used to calculate ejection fraction (an important measure of heart performance) and evaluate regional myocardial wall motion.


Purpose

A MUGA scan may be done while the patient is at rest and again with stress. The resting study is usually performed to obtain the ejection fraction of the right and left ventricles, evaluate the left ventricular regional wall motion, assess the effects of cardiotoxic drugs (i.e., chemotherapy), and differentiate the cause of shortness of breath (pulmonary vs. cardiac). Ejection fraction and wall motion are also important measurements made during a stress study, but the stress study is performed primarily to detect coronary artery disease and evaluate angina.

Description

The MUGA scan is a series of images that demonstrate the flow of blood through the heart, providing information about heart muscle activity. Before images are taken, a radionuclide is injected into the bloodstream, a process that requires two injections in most health care facilities. The first injection contains a chemical that adheres to red blood cells, and the second contains a radioactive tracer (Tc99m) that attaches to that chemical. Alternatively, the two chemicals can be mixed together first and then injected, but the material tends to accumulate in bone and may obscure the heart.

The pictures are taken via gamma camera driven by a computer program that times the images, processes the information, and performs the mathematical calculations to provide ejection fraction and demonstrate wall motion. Images are obtained at various intervals during the cardiac cycle. Electrodes are placed on the patient so that a time frame can be established, for example, the time period between each "wave" (a part of the cardiac cycle seen on an EKG). The time frame is divided into several intervals, or "multiple gates." The result is a series of pictures showing the left and right ventricles at end-diastole (when the heart is dilated and filled with blood) and end-systole (when the heart is contracted and blood is being pumped out), and a number of stages in between.

A MUGA scan is performed in a hospital nuclear medicine department or in an outpatient facility. It takes approximately 30 minutes to one hour. The patient lies down on a bed alongside the gamma camera, receives the radionuclide injections, and multiple images are taken. If a stress study is indicated, the rest study is performed first. In a stress study, the patient usually lies on a special bed fitted with a bicycle apparatus. While an image is being recorded, the patient is asked to cycle for about two minutes, then the resistance of the wheels is increased. After two more minutes of exercise , another image is obtained and the resistance is increased again. Blood pressure and ECG are monitored during the procedure. After the stress portion is finished, one more resting, or recovery, study is obtained.


Preparation

Standard preparation for an ECG is required. Special handling of nuclear materials by a nuclear medicine technologist may be required for the injections.


Aftercare

The patient may resume normal activities immediately following the test.

Normal results

A normal MUGA scan should not demonstrate areas of akinesis (lack of movement), or hypokinesis (decreased movement) of the heart muscle walls. Abnormal motion, especially in the left ventricle, is suggestive of an infarct or other myocardial defect. The ejection fraction is a measure of heart function, and should be within the normal limits established by the testing facility.


Resources

books

DeBakey, Michael E. and Gotto, Antonio M., Jr. "Noninvasive Diagnostic Procedures." In The New Living Heart. Holbrook, MA: Adams Media Corporation, 1997, pp. 5970.

Klingensmith III, M.D., Wm. C., Dennis Eshima, Ph.D., John Goddard, Ph.D. Nuclear Medicine Procedure Manual 2000-2001.

"Radionuclide Angiography." In Cardiac Stress Testing & Imaging, edited by Thomas H. Marwick. New York: Churchill Livingstone, 1996, pp. 51721.

Raizner, Albert E. "Nuclear Cardiology Testing." In: Indications for Diagnostic Procedures: Topics in Clinical Cardiology. New York, Tokyo: Igaku-Shon, 1997, pp. 4447.

Texas Heart Institute. "Diagnosing Heart Diseases." In Texas Heart Institute Heart Owner's Handbook. New York: John Wiley & Sons, 1996, p. 333.

Ziessman, Harvey, ed. The Radiologic Clinics of North America, Update on Nuclear Medicine. Philadelphia: W.B. Saunders Company, 2001.

organizations

American Heart Association. National Center. 7272 Greenville Avenue, Dallas, TX 75231-4596. (214) 373-6300. <http://www.medsearch.com/pf/profiles/amerh/>.

Texas Heart Institute Heart Information Service. P.O. Box 20345, Houston, TX 77225-0345. (800) 292-2221. <http://www.tmc.edu/thi/his.html>.


Christine Miner Minderovic, B.S., R.T., R.D.M.S.
Lee A. Shratter, M.D.

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"Multiple-Gated Acquisition (MUGA) Scan." Gale Encyclopedia of Surgery: A Guide for Patients and Caregivers. . Retrieved August 18, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/multiple-gated-acquisition-muga-scan-0