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Non-Invasive Tests

MIBI Stress Test

Thallium and sestamibi stress tests are nuclear imaging methods that provide a view of the blood flow into the heart muscle. The thallium and sestamibi tests are also called “MIBI stress test”, and are used to evaluate how well your heart is perfused (supplied with blood) at rest as compared with activity.

During these tests, heart images can be obtained because the patient receives an injection of a substance that is labeled with a radioactive marker or radiotracer to make it visible in the bloodstream. These substances are also called radiopharmaceuticals, and include thallium-201 and technetium-99m MIBI or sestamibi.
Sestamibi stress tests are more accurate and provide additional information.  

Why the test is performed

The thallium and sestamibi stress tests are indicated when your doctor needs to evaluate for example:  

  •  how well your heart responds to exercise

  •  the cause of your chest pains

  •  the degree of blockage in your coronary arteries

  •  what to expect after you have had a heart attack

  •  how well a heart procedure done to improve blood flow in your coronary arteries is working

How to prepare for the test

You will be instructed to wear comfortable clothes and shoes with non-skid soles. You will probably be asked not to eat or drink anything after midnight, except for a few sips of water if you need to take medicines.
The entire test may last about 4 hours, so you will need to prepare accordingly. At some point during your stay for the test you will likely be given a long break and be allowed to have lunch or a snack at a nearby cafeteria. During the test you will not be sedated and therefore once the test is completed you will be able to drive yourself home.  

How the test will feel

You may feel the same symptoms as with a regular stress test or with a session of strenuous exercise: fatigue, muscle cramps in your legs or feet, some shortness of breath, or chest pain.  

How the test is performed

In a medical center, you will be instructed to exercise as hard as you can on a treadmill or bicycle.
When you reach your maximum level of exercise, a nurse will inject in your vein a small amount of a radioactive substance (radiotracer), either thallium or sestamibi. The radiotracer will travel in the bloodstream and, through the coronary arteries, will enter into the heart muscle as you complete your exercise session.
After you finish exercising, you will lie down on a special table under a bulky camera called a gamma camera. The gamma camera can scan your heart and detect the radiotracer in it. The distribution of the radiotracer in your heart will be processed by a computer to create pictures of your heart. The first pictures are made shortly after the exercise test, to show the circulation of blood to your heart during exercise. This is the part considered "a stress test" and is the most challenging for your heart.
Then you will need to lie quietly for 2-3 hours, and at that point the scanner will make another series of pictures of your heart. These images will show the circulation of blood through your heart muscle at rest.  

• Special Considerations

However, some patients cannot exercise adequately. Patients with lung disease, arthritis, or disease in the leg vessels may not be able to walk. Patients with some medical conditions should not walk on the treadmill. For these patients the doctor can use a drug to effect the blood supply to the heart and simulate the effects of exercise. The drug may be persantine (dipyridamole), dobutamine, or adenosine. The drug is used with a radioactive substance (isotope) to assess the blood supply to the heart.

If your doctor has indicated that your test should be performed without exertion, then at the beginning of the test you will not exercise, but instead will receive an intravenous medication, a vasodilator (usually dipyridamole or adenosine). This medication will selectively dilate (widen) the coronary arteries as long as they are normal; arteries with blockages will receive less blood flow and will be less dilated, allowing less blood flow into the heart muscle. After this initial medication, you will receive the injection with the radiotracer. The test done using a vasodilator can potentially show a defect in the same way as the test with exercise does.  

Normal Values

When a normal amount of the radiotracer arrives into all areas of the heart, the heart images are obtained are normal. The heart images at peak exercise are compared to the heart images at rest. If during both exercise and rest all images are normal, then your blood flow through the coronary arteries is considered to be normal.  

What abnormal results mean

In your heart pictures, an area may lack the radiotracer and thus show a spot of a different color, called a “defect”. Defects represent poor uptake of the radiotracer by the heart because of reduced blood flow. When a defect occurs at peak exercise and not at rest, the most likely cause is a significant blockage of a coronary artery. When a defect is observed both at rest and with exertion, that indicates that previous damage from a heart attack has occurred and that the heart muscle has a scar.

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