This is a type of nuclear scanning test or myocardial perfusion imaging test. It shows how well blood flows to the heart muscle. It's usually done along with an exercise stress test on a treadmill.
What to Expect:
When you reach your maximum level of exercise in your stress test, a small amount of a nuclear material is injected into the bloodstream. Then you will lie down on a special table under a camera, known as a "gamma camera," that can see the nuclear material and take pictures. The nuclear material mixes with the blood in the bloodstream and heart's arteries and enters heart muscle cells. If a part of the heart muscle doesn't receive a normal blood supply, less than a normal amount of nuclear material will be in those heart muscle cells.
The first pictures are made shortly after your exercise test and show blood flow to the heart during exercise. The heart is "stressed" during the exercise test — thus the name "stress test." The clinical staff will then ask you to wait for 2-3 hours and then takes another series of pictures. These show blood flow to the heart muscle during rest and are compared with the earlier set of pictures.
Why It Is Done:
The myoview or thallium stress test is useful to determine:
- Extent of a coronary artery blockage
- Prognosis of patients who've suffered a heart attack
- Effectiveness of cardiac procedures done to improve circulation in coronary arteries
- Cause(s) of chest pain
- Level of exercise that a patient can safely perform
What Does the Test Show?
- If the test is normal during both exercise and rest, then blood flow through the coronary arteries is normal. The coronary arteries supply blood to the heart muscle.
- If the test shows that perfusion (blood flow) is normal during rest but not during exercise (a perfusion defect), then the heart isn't getting enough blood when it must work harder than normal. This may be due to a blockage in one or more coronary arteries.
- If the test is abnormal during both exercise and rest, there's limited blood flow to that part of the heart at all times.
- If no thallium is seen in some part of the heart muscle, the cells in this part of the heart are dead from a prior heart attack. (They have become scar tissue.)
What if I Can't Perform an Exercise Test?
Sometimes you can't do an exercise test because you're too sick or have physical problems. In this case, a drug such as dipyridamole is given. This drug increases blood flow to the heart and thus "mimics" an exercise test. Then the thallium test is given.