Cardiolyte/Thallium Scan

What Is an Exercise Cardiolyte/Thallium Scan?

A thallium scan is a test that uses a radioactive substance (known as a tracer) to produce images of the heart muscle. When combined with an exercise test, the thallium scan helps determine if areas of the heart do not receive enough blood.

The exercise thallium scan is especially useful in diagnosing coronary artery disease, the presence of blockages in the coronary arteries (the vessels that supply oxygen-rich blood to the heart muscle).

Is The Exercise Cardiolyte/Thallium Scan Safe?

The radiation exposure during a cardiolyte/thallium scan is extremely small, and the doses used are safe. Cardiolyte/thallium is excreted rapidly by the kidneys. However, if you are pregnant, suspect you may be, or are a nursing mother, discuss the matter with your doctor.

The exercise test is also safe. A small amount of risk does exist, however, because it stresses the heart. Possible rare complications include abnormal heart rhythms and a heart attack. Experienced personnel are available to handle any emergency.

What Do Cardiolyte/Thallium Scans Show?

During the test, a tiny amount of thallium tracer is injected into a vein in your arm while you walk on a treadmill. For patients who cannot exercise, the test may be done after the injection of a drug that produces a stress on the heart similar to exercise.

The tracer travels in the bloodstream, is carried through the coronary arteries, and is picked up by the heart muscle cells. Areas of the heart muscle that have an adequate blood supply pick up the tracer almost immediately. Areas that do not have an adequate blood supply pick up the tracer very slowly or not at all. This will show up as a lighter area, called a "defect".

A second set of images is taken several hours later, while you are at rest. These images help differentiate between areas that temporarily do not receive enough blood (the defect returns to normal) and areas that are permanently damaged from a previous heart attack (the defect persists).

Preparing For Tests

What Happens During Tests?

The exercise cardiolyte/thallium test is usually performed at a clinic or hospital, in the nuclear medicine or radiology department.

The test has two parts: the exercise portion and the imaging portion.

Exercise Portion

The exercise portion of the test can be performed in the doctor’s office or at the hospital. A trained technician will place several electrodes (small sticky patches) on your chest and shoulders to allow recording of the ECG during exercise. Wires link the electrodes to an ECG machine. A cuff will be applied to your arm to monitor your blood pressure during the test.

You will be shown how to step onto the treadmill and how to use the support railings to maintain your balance. The treadmill starts slowly, and then the speed and incline are increased gradually.

Your blood pressure will be checked every few minutes, and the ECG will be carefully watched for abnormal changes. You will be instructed to report any symptoms, such as chest pain, shortness of breath, leg fatigue, or dizziness.

The test may end when you become too tired to continue or when you experience significant symptoms. Other times, the test may be stopped when you reach your peak heart rate or when your ECG shows abnormal changes.

After the exercise portion of the test is over, you will be helped to a chair or a bed. Your blood pressure and ECG will be monitored while you recover. The technician will remove the electrodes and cleanse the electrode sites. The test typically takes between 45 minutes to one hour, which includes preparation for the test, the exercise portion, and the recovery period.

Imaging Portion

You will lie flat on a special table under a scanning camera. During imaging, the camera takes pictures at various angles. You should remain still while the pictures are being taken. This part of the test usually takes 10-20 minutes.

After the initial set of pictures, you will be asked to remain relatively quiet for the next 2-4 hours. You may leave the area, and may be allowed limited beverages, but no solid food.

When you return, you will have additional pictures taken, without repeating the exercise. These pictures represent the heart in its resting state. In some cases, more pictures are taken the next day.

The Benefits

The exercise thallium scan is generally more accurate and provides more information than an exercise ECG test. This information helps your doctor make an accurate diagnosis and develop a treatment plan that’s best for you.

The Results

The doctor conducting the test may be able to give you preliminary results before you leave. A complete interpretation, however, usually takes several days.