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What is a thallium stress test?

Thallium Stress TestThis 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 or bicycle.

The 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

When the patient reaches his or her maximum level of exercise, a small amount of a radioactive substance called thallium is injected into the bloodstream. Then the patient lies down on a special table under a camera ("gamma camera") that can see the thallium and make pictures. The thallium 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 thallium will be in those heart muscle cells.

The first pictures are made shortly after the 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 patient then lies quietly for 2-3 hours and another series of pictures is made. These show blood flow to the heart muscle during rest.

What does the thallium stress 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.)
Can I eat or drink on the day of the test?
  • The short answer is no. However, you may drink small sips of water to help you swallow your medications
  • Avoid all products containing caffeine for 24 hours before the test. In general, caffeine is found in coffee, tea, colas and other soft drinks as well as most chocolate products.
  • Also avoid decaffeinated or caffeine-free products for 24 hours before the test, as these product contain trace amounts of caffeine.
  • DO NOT SMOKE ON THE DAY OF THE TEST, as nicotine will interfere with the results of your test.
Should I take my medications the day of the test?

Please bring a copy of all of your medications, including over-the-counter medications and supplements that you routinely take, to the test appointment.

Please follow these guidelines about taking your medications the day of the test:

Medications with caffeine: DO NOT take any over-the-counter medication that contains caffeine (such as Excedrin, Anacin, diet pills and No Doz) for 24 hours before the test. Ask your physician, pharmacist or nurse if you have questions about other medications that may contain caffeine

If you have asthma: Your physician will tell you NOT to take theophylline (Theo-dur) for 48 hours before the test. Please plan to bring your asthma inhaler mediation to the test.

If you have diabetes: If you take insulin to control your blood sugar, ask your physician how much insulin you should take the day of the test. Your doctor may tell you to take only half of your usual morning dose and to eat a light meal 4 hours before the test. If you take pills to control your blood sugar, do not take your medication until after the test is complete. Bring your diabetes medications with you so you can take it when the test is complete. Do not take your diabetes medication and skip a meal before the test.

If you own a glucose monitor, bring it with you to check your blood sugar levels before and after your test. If you think your blood sugar is low, tell the lab personnel immediately. Plan to eat and take your blood sugar medication following your test.

Your physician may also ask you to stop taking other heart medications on the day of your test. If you have any questions about your medications, ask your physician. Do not discontinue any medication without first talking with your physician.
What to expect during the test
Your test will take place in Nuclear Medicine located at JB-3 (in the basement of the Miller Family Pavilion). The testing area is supervised by a physician.

A nuclear medicine technologist will place an IV into a vein in your arm or hand and inject a small amount of radioactive tracer. The tracer is not a dye or contrast. After the tracer is injected, you will wait about 30 minutes before the first set of "resting" images are taken.

Then you will be asked to lie very still under the gamma camera with both arms above your head for about 15 to 20 minutes. The camera will record images that show blood flow through your heart at rest.

Next, a technician will place electrodes on your chest to monitor your EKG.

Before the medication is infused into the IV, the technician will discuss the possible side effects so you will know what to expect.

If you are able, you will slowly walk on a treadmill during the administration of the medication. Otherwise, you will lie on the exam table for the duration of the test.

Your heart rate, EKG and blood pressure will be monitored throughout the test.

After waiting about 30 minutes, you will be asked to again lie very still under the camera with both arms over your head for about 15-20 minutes. The camera will record images that show blood flow through your heart during cardiac stress/activity. These images will be compared to the first set.

How long will the test last?

The appointment will take about 3-4 hours. The first part of the appointment will take about 90 minutes. The second part of the appointment will take about 2-3 hours.

If you weigh over 300 pounds, your test may be scheduled as a two-day test.
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 (di-pi-RID'ah-mol) or adenosine is given. This drug increases blood flow to the heart and thus "mimics" an exercise test. Then the thallium test is given.