Thallium and sestamibi stress tests are nuclear imaging methods that provide a view of the blood flow into the heart muscle, both at rest and during activity.

These tests are also called MIBI stress test and myocardial perfusion scintigraphy.

This test is done at a medical center. You will be told to exercise as hard as you can on a treadmill or bicycle.

After reaching your maximum level of exercise, a health care provider will inject a radioactive material into a vein, usually either thallium or sestamibi. The material will travel in the bloodstream, through the coronary arteries, and into the heart muscle as you complete your exercise session.

Next, you will lie down on a table under a special camera that scans the heart and detects the radioactive material. A computer will look at how the material has collected and create pictures of the heart. The first pictures are made shortly after the exercise test, which shows blood flow to the heart during exercise. This part is called a "stress test" and is the most challenging for your heart.

After lying quietly for a few hours, you'll have more pictures of the heart taken. These images show blood flow through your heart during rest.

If your doctor does not think exercise is safe for you, or if you have joint problems that may make doing so difficult, you will be given a drug called a vasodilator that will make your heart feel as if you were exercising. This medicine widens normal blood vessels to the heart, which increases blood flow. Arteries with blockages will narrower, and therefore will receive less blood. After you receive this medicine, you will receive the radioactive material, as described above. The test done using a vasodilator can potentially show a heart problem in the same way as the exercise 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.

For one entire day prior to the test, you will be required to abstain from caffeine and certain medications. Caffeine is in food and beverages such as all regular and decaffeinated coffees or teas, chocolate products, many sodas, and certain pain relievers. These are just a few examples. Please read the labels of your food and beverages carefully, because caffeine consumed before the test may invalidate the test results.

Medications that you may need to stop taking before the test include some asthma medicines and medicines for chest pain (angina); check with your doctor. If you take insulin to control your blood sugar, ask your physician if or how much insulin you should take the day of the test.

The entire nuclear imaging 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.

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.

If you will not be exercising but will be receiving a vasodilator injection, you may feel a sting as the medication goes into the IV, which may be followed by a feeling of warmth. Some patients also develop a headache or nausea.

If any of the symptoms listed above appear during your test, let the lab personnel know immediately.

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

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.

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.

Nuclear imaging stress tests are very safe. The estimated risk of complications are only about 1 in 1,000 to 1 in 2,000 cases. These complications involve rare skin rashes, large fluctuations in blood pressure, arrhythmias, and difficulty breathing or asthma-like reactions. These, and any additional risks that may apply specifically to you, will be explained to you in advance by your doctor and by the health care provider performing the test.

Radiation exposure to radiotracers can be a concern for the nuclear lab staff, but not for patients undergoing an occasional nuclear imaging test.

Sometimes a thallium or sestamibi test produces heart image that looks like a defect, but it’s a pseudo-defect that gives a “false positive” test result (i.e., a falsely abnormal test). This is due to interference with the heart image from non-heart tissues such as the diaphragm (diaphragm attenuation), and, in women, the breast tissue ("breast attenuation").

When non-heart tissue attenuation is clearly the cause of an abnormal image, nothing additional needs to be done. If an attenuated image instead is thought to coincide with a true defect or area of ischemia (reduced blood flow), then your doctor may recommend additional testing such as a stress echocardiogram or a cardiac catheterization.