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Also known as “thallium or sestamibi stress testing,” this procedure is almost identical to exercise stress testing. After the patient is attached to an electrocardiogram (EKG) and a blood pressure machine, exercise is started on a treadmill, a stationary bicycle, or a stair machine. With the nuclear test, a radioactive isotope, thallium or sestamibi, is injected in an arm vein and the thallium is absorbed into the heart muscle for several hours.

Scans are performed immediately after exercise and several hours later to detect a lack of blood supply to the heart. The test continues until fatigue or symptoms develop.

Why is it performed?

Nuclear stress testing is performed to evaluate the condition of the heart and the arteries that supply it. During exercise, the heart has a greater need for blood and the oxygen and other nutrients within it. If the coronary arteries are partially or totally blocked, they will not be able to meet that demand, creating a condition called cardiac ischemia — inadequate blood supply to the heart muscle. Monitoring the thallium blood flow in the heart, and the amount of time that it remains there, reveals abnormalities in the heart and coronary arteries. Areas where a heart attack has occurred stay abnormal for several hours while areas that have only been ischemic during the exercise test show some improvement over time.

What is experienced?

Patients may be told to discontinue certain medications before the test day. Patients should dressed for exercise in slacks, a shirt, and sneakers. Button down tops allow easy access for the EKG electrodes.

The heart is “stressed” with either physical exercise on a treadmill or stationary bike, or the patient receives an intravenous medication (usually Persantine or Dobutamine) that will cause the heart to work harder. The tests ends when the heart rate reaches just below maximal levels, the EKG shows abnormal heart rhythms, symptoms develop or the blood pressure goes too high or too low. If pain, shortness of breath, dizziness, or exhaustion is experienced, the test is ended. At this point, an intravenous injection is given and the nuclear scan is taken while the patient reclines.


EKG electrodes are attached to the chest and a blood pressure cuff is placed around the upper arm.

Depending on the patient’s response to stress, the test could last from one to 15 minutes. When the doctor decides that the exercise stress has been sufficient, the exercise machine is stopped, and an intravenous injection of the radioactive material is given.

Radiology scans record the flow of radioactive material in the heart. Sometimes the scan is repeated two to three hours later to discern whether an area’s blood flow is still decreased or has normalized.

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