Thallium Stress Test
What is a thallium stress test (also called a Nuclear Stress Test)?
A thallium stress test is an exercise stress test that is
performed in the nuclear scanning section of the radiology
department. It uses the same principles as the exercise stress
test, but provides significantly more information. In addition
to the procedures conducted in an exercise
stress test, a radioactive isotope called thallium is
injected into the bloodstream during peak exercise. This dye
is absorbed by the heart. A computer provides images of the
heart and gives specific information about the circulation
from the coronary arteries in the heart muscle. A second scan
is performed at rest about 3 hours later to compare the images
of your heart at rest and with exercise.
The results of a nuclear stress test are evaluated in two ways: (1) the Inova cardiologist looks at the EKG, blood pressure response and any symptoms experienced during the test (see exercise stress test), (2) the Inova radiologist evaluates the computer images and looks for "defects" or lack of dye uptake into specific areas of the heart muscle. Lack of dye uptake correlates with a lack of oxygen in a specific area of the heart.
There are two types of defects:
- A "perfusion defect" after exercise, but not at rest. This reflects a lack of bloodflow and oxygen in a specific coronary artery and specific area of the heart because of a partial blockage during exercise only. The scans show the lack of dye absorbed in a specific area of the heart (the perfusion defect) when the oxygen demand of the heart is greater during exercise and exceeds the supply because of coronary artery narrowing. The affected muscle will absorb the dye at rest because the oxygen demand does not exceed the oxygen supply at a resting heart rate. This is considered a "positive" test.
- A "perfusion defect" with exercise and at rest. This usually reflects a complete blockage as a result of a previous heart attack or heart damage. The area is scar tissue. No dye is absorbed into this area at rest or with exercise. In other words, there are no living cells in this part of the heart muscle.
A normal test would show no "perfusion defects" at rest or with exercise. In this situation, the heart muscle and coronary arteries are considered normal.
Preparing for the procedure
Do not eat or drink for at least 4 hours before the test (or as directed). Your Inova physician may instruct you to stop taking certain medicines. You will have an intravenous (IV) line placed in your arm.
During the procedure
Electrocardiogram patches will be placed on your chest to record an EKG. You will exercise briefly on a treadmill. In some cases, instead of exercising, the physician may administer a medication that makes the heart work harder. Thallium will be injected into your IV, and you will be asked to lie still while pictures are taken.
After the procedure
Resume normal activities. Your Inova physician will inform you of the test results.
