Nuclear (Thallium) Stress Test

A nuclear stress test allows doctors see pictures of the heart during rest and shortly after exercise. This test provides information about the size of the heart’s chambers, how well the heart is pumping blood, and whether or not the heart has any damaged or dead muscle. Nuclear stress tests also assess whether or not arteries are narrowed or blocked due to coronary artery disease.

How It Works

This test is similar to the exercise stress test, except that patients are injected with a small amount of a radioactive dye before the end of the exercise part of the test. This dye is not harmful.

A nuclear stress test can help doctors determine if the heart is working properly during rest, exercise, or both. Blood flow to heart may be normal at rest but abnormal during exercise (or times of stress) because the heart normally pumps more blood during times of physical exertion. Blood flow to the heart may be abnormal during both parts of the test (rest and exercise), indicating that part of the heart is permanently deprived of blood. If the radioactive substance is not absorbed into part of the heart, it could indicate that that section of heart muscle has died (due to a previous heart attack or blocked coronary arteries).

What To Expect

Patients will receive protocols from their doctors regarding eating, drinking, and smoking prior to the test and regarding taking medication before the test, including insulin and inhalers. Patients should wear exercise clothing and shoes. Lotions or creams should not be used on the day of the test.

The electrocardiogram (EKG), blood pressure cuff, and other monitoring devices are placed. Baseline recordings are taken. During the test, the patient is asked to walk on a treadmill or to ride a stationary bike. Every 2 or 3 minutes, the doctor or the technician increases the speed and slope of the treadmill or stationary bike. At regular intervals, the testing personnel will ask how the patient is feeling. Chest, arm or jaw pain or discomfort; shortness of breath; dizziness; lightheadedness; or any other unusual symptoms should all be reported. It is normal for the patient’s heart rate, blood pressure, breathing rate, and perspiration to increase during the test. The doctor or technician watches for changes in the EKG patterns, blood pressure, and pulse, including any changes that might suggest that the test should be stopped. The patient is asked to exercise vigorously until exhaustion.

At the end of the test, a cool-down phase allows the patient to walk or pedal slowly, then lie down or sit quietly while the monitoring is concluded and the heart rate, blood pressure, and respirations return to normal. Although the appointment lasts about 60 minutes, the actual exercise time is usually between 7 and 12 minutes.

After completing the exercise part of the test, the patient is given an injection of a radioactive substance and asked to lie on an examination table with a gamma-ray camera above it. The camera detects traces of the radioactive substance and sends the pictures to a television monitor.

The patient is then allowed to leave the testing area for 3 or 4 hours. The doctor provides instructions regarding exercise, eating, and drinking during that time. When the patient returns, he or she is given another injection of the radioactive substance and asked to repeat the pictures. After the test, normal activities may be resumed.

Texas Heart Institute