Multiple Gated Acquisition - MUGA for short - measures how well your heart is functioning as a pump, much like an echo does, but more accurately. The MUGA measures how much blood your heart pumps, or "ejects" with each contraction (EF) and how quickly that blood is ejected. EF is actually figured with a mathematical formula : EF = (end diastolic volume - end systolic volume) divided by (end diastolic volume - background). The nuclear camera (gamma camera) can separate left heart function from right heart function by using a certain view, called left anterior oblique.
Because this test is very accurate for measuring EF, it is preferred by some doctors. However, MUGA equipment is both more scarce and more expensive than echo equipment. It requires an injection of a radioactive material and is also more uncomfortable for the patient. MUGA does not "see" valve disease as well as an echo. If you have lung disease, this is the test of choice to measure EF because echo does not work well for people with lung disease.
Remember that with this test, images that are taken during irregular beats are rejected. That's why patients with multiple odd ventricular beats like PVCs require longer scan times to gather enough "good data." MUGA is not suited for patients with a really irregular heart rhythm. Echo has the same problem but not as badly.
An intravenous line will be used for this test. A liquid containing a radioactive substance will be given through it in one of two ways. This substance labels or "tags" red blood cells with a tiny bit of radioactivity so the blood cells can be clearly seen in pictures taken with the gamma camera.
With the in-vivo method, stannous chloride is injected first. This accumulates inside red blood cells. About 20 minutes later, the radioactive substance is injected.
With the in-vitro method, some of your blood is drawn and the stannous chloride is injected into the blood sample inside a container. The radiactive substance is then injected into the blood sample. Then the blood is injected back into you.
Either way, the stannous chloride dilutes the radioactive substance and keeps it from seeping back out of your red blood cells during the test. Both methods require you to wait for the blood to circulate thoroughly throughout your body before the test begins, perhaps as long as 20 to 30 minutes.
For the picture-taking part of the MUGA, you will lie flat on a very narrow table. You will be hooked to an EKG monitor, and asked to lie very still. By counting the "tagged" red blood cells over the course of many heart beats, a nuclear camera can make a picture of your heart's chambers and the large blood vessels leading to and from it. The nuclear camera may look different from hospital to hospital but will make several "passes" over your body to accurately track the movement of blood through your arteries and heart. At least one of your arms will be in a very uncomfortable position over your head. They may offer to tape your arms in position because you must lie very still. Some people recommend this - others don't. You may be asked to vary position 2 or 3 times but each position must be held very still for at least 10 minutes each. The test should take about 45 minutes.
No side effects are known, although it is always possible when you are being injected with something that you could have a bad reaction. Drugs containing aminophylline, such as asthma relievers, should be avoided for at least 24 hours before the test, and if you are taking any kind of steroids - like prednisone - you should tell the doctor before taking the test.
Relax. The substances injected into you for this test have been tested on a large number of people and are pretty safe. Do not take your Lasix before this test. Stopping for a quick pee is going to be out of the question. Bring something to read. You have to wait a lot during this process and reading material may help. If you have a chronic cough due to CHF or ACE inhibitor, consider asking your doctor for a cough suppressant for this test to prevent you from messing up the results by hacking away in the middle of a "lie very still" period. Do so several days in advance to be sure you have it on hand for the test. There are several effective prescription cough suppressants safe for CHFers.
In Australia, this test may be called a GHPS, or Gated Heart Pool Scan. You can also find information about this test under the topic "radionuclide ventriculography." If you're not sure that your health insurance will pay all the cost of a MUGA, find out beforehand because this is a very expensive test.
All information on this site is opinion only. All concepts, explanations, trials, and studies have been re-written in plain English and may contain errors. I am not a doctor. Use the reference information at the end of each article to search MedLine for more complete and accurate information. All original copyrights apply. No information on this page should be used by any person to affect their medical, legal, educational, social, or psychological treatment in any way. I am not a doctor. This web site and all its pages, graphics, and content copyright © 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004 Jon C.