A thallium stress test is a nuclear imaging test that shows how well blood flows into the heart during exercise and at rest. A radioisotope (nuclear material) is administered intravenously. It settles into the heart muscle and pinpoints spots that are abnormal.
Your doctor may order a thallium stress test:
- if he or she suspects your heart is not getting enough blood flow (oxygen) when it’s under stress such as exercise
- if you have chest pain or worsening angina
- if you’ve had a previous heart attack
- to check how well medications are working
- to determine whether or not a procedure or surgery was successful
- to determine if your heart is healthy enough to start an exercise program
The thallium stress test can show:
- the size of the heart chambers
- how effectively the heart pumps (ventricular function)
- how well the coronary arteries supply the heart with blood (myocardial perfusion)
- if there is damage or scarring of the heart muscle from previous heart attacks
The test must be done at a hospital, medical center, or doctor’s office. A nurse or health care professional will insert an intravenous line (IV) usually on the inside of the elbow. A radioisotope or radiopharmaceutical medication called thallium or sestamibi is injected through the IV. You will then lie down for 15 to 45 minutes while the medication settles in the heart.
A special nuclear camera is used to take pictures of your heart, projecting them onto a computer screen. The doctor can then analyze these images to evaluate how weak or strong your blood flows to the heart.
If you’re able to exercise, you’ll be asked to walk on a treadmill or pedal an exercise bicycle. You will likely be asked to start slowly and progressively pick up the pace, into a jog. You may even be asked to run on an incline to make it more challenging. For patients that can’t exercise, the doctor will you give you a medication that will stimulate your heart and make it beat faster. This is to simulate exercise.
Your blood pressure and heart rhythm are monitored while you exercise. Once your heart is working at full capacity, you will be given another radiopharmaceutical injection and wait for 15 to 45 minutes. Images of your heart will be taken for your doctor to analyze the strength of your blood flow to your heart. You will then have more pictures taken of your heart with the camera.
Your doctor will view the images of your heart taken before and after vigorous exercise.
You will likely fast after midnight the night before your test. Wear comfortable clothes and shoes for exercising. Twenty-four hours before the test, you will need to avoid all caffeine, including tea, soda and coffee, chocolate, and pain relievers that contain caffeine.
Your doctor will need to know all medications that you are taking. This is because some, like asthma medications, interfere with test results. Your doctor will also want to know if you’ve taken any erectile dysfunction medication including Viagra, Cialis, or Levitra 24 hours before the test.
Most people tolerate the test very well. You may feel a sting as the medication that simulates exercise is injected, followed by a warm feeling. Some patients may experience headache, nausea, and a racing heart.
Complications from the test are rare, but may include:
- arrhythmias (irregular heart beat)
- increased angina (pain from poor blood flow in the heart)
- difficulty breathing
- asthma-like symptoms
- large swings in blood pressure
- skin rashes
- shortness of breath
- chest discomfort
- heart palpitations (an irregular heart beat)
If any of these symptoms occur during your test, alert the test administrator immediately.
Results depend on the reason for the test, how old you are, your history of heart problems and other medical issues.
A normal result means blood flowing through the coronary arteries in the heart is normal.
Abnormal results may indicate:
- reduced blood flow to part of the heart (narrowing or blockage of one or more arteries that supply your heart muscle)
- scarring of the heart muscle due to a previous heart attack
- coronary artery disease (heart disease)
- a too-large heart (indicating other heart complications)
Depending on the reason for your test, you may need further testing to evaluate the exact problem. You may also need a procedure or surgery to unblock a blockage, or you may need to change medication. Your doctor will develop a treatment plan specifically for you.