Nuclear stress test
Thallium stress test is a nuclear imaging method that shows how well blood flows into the heart muscle, both at rest and during activity.
How the Test is Performed
This test is done at a medical center. The test is done in two parts:
Part 1: You will walk on a treadmill (or pedal on an exercise machine).
- Gradually you will be asked to walk (or pedal) faster and on an incline.
- If you are not able to exercise, your doctor will give you a medicine called dobutamine. This medicine will make your heart beat faster and harder, similar to when you exercise.
- Your blood pressure and heart rhythm (ECG) will be watched (monitored) the whole time.
Part 2: The health care provider will inject a radioactive substance into one of your veins and then take pictures of your heart.
- The radioactive material may be thallium or sestamibi. (If sestamibi is used, it's called a "sestamibi stress test.") This substance travels through your bloodstream into the heart muscle.
- Next, you will be asked to lie down on a table under a special camera that scans the heart. A computer creates pictures of the heart by tracking how the radioactive material moves through the area.
The first pictures are taken shortly after you get off the treadmill or are given the vasodilator drug. These images show how blood flows to the heart during exercise. This is the part most commonly referred to as the "stress test," because it is the most challenging for your heart.
After lying quietly for a few hours, you'll have more pictures taken of the heart. These images show blood flow through your heart at rest.
The entire test can take about 4 hours. You will usually be given a long break in between scans and allowed to have a caffeine-free lunch or a snack at a nearby cafeteria.
How to Prepare for the Test
You should wear comfortable clothes and shoes with nonskid 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.
You will need to avoid caffeine for 24 hours before the test. This includes caffeinated beverages such as tea, coffee, and sodas, as well as chocolates, and certain pain relievers.
Your doctor will tell you if you need to stop taking any medicines before the test. Medications used to treat asthma and angina may interfere with test results. Never stop taking any medicine without first talking to your doctor.
It is important to tell your doctor if you have taken a dose of the following medications within the last 24 hours:
How the Test Will Feel
- Sildenafil citrate (Viagra)
- Tadalafil (Cialis)
- Vardenafil (Levitra)
Some people feel fatigue, muscle cramps in the legs or feet, shortness of breath, or chest pain during the treadmill test.
If you are given the vasodilator drug, you may feel a sting as the medication is injected, followed by a feeling of warmth. Some patients also have a headache, nausea, and a feeling that their heart is racing.
Rarely, during the test people experience:
- Chest discomfort
- Shortness of breath
If any of the symptoms listed above appear during your test, let the lab personnel know immediately.
Why the Test is Performed
The test is done to see whether your heart muscle is getting enough blood flow, and therefore enough oxygen, when it is working hard (under stress).
Your doctor may order this test to determine:
- How well a treatment (medications, angioplasty, heart surgery) is working
- If you are at high risk for heart disease before you start an exercise program or have surgery
- The cause of new chest pain or worsening angina
- What you can expect after you have had a heart attack
The results of a nuclear stress test can help your doctor:
- Determine how well your heart is pumping
- Determine the proper treatment for coronary heart disease
- Diagnose coronary artery disease
- See whether your heart is too large
A normal result means blood flow through the coronary arteries is normal.
Note: Normal value ranges may vary slightly among different medical centers. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
Abnormal results may be due to:
- Reduced blood flow to a part of the heart. The most likely cause is a blockage of the arteries that supply your heart muscle.
- Scarring of the heart muscle due to a previous heart attack
After the test you may need:
- Angioplasty and stent placement
- Changes in your heart medicines
- Coronary angiography
- Heart bypass surgery
Complications are rare but may include:
- Increased angina pain during the test
- Difficulty breathing or asthma-like reactions
- Extreme swings in blood pressure
- Skin rashes
Your health care provider will explain the risks before the test.