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How is a nuclear stress test performed?

During a nuclear imaging test, you will either exercise on a treadmill to make your heart work harder or be injected with a medication that can induce ischemia (in which the heart is deprived of oxygen). You also get an injection of a tracer, a slightly radioactive substance (technetium or thallium) that circulates in the bloodstream. The single-photon emission computed tomography (SPECT) scanner tracks blood flow through the heart by detecting these radioactive particles in the bloodstream. The tracers concentrate in areas of the heart muscle that have a good blood supply, while areas with no blood supply, such as scars from a previous heart attack, won't collect the radioactive particles.

You wait a short time for the tracers to reach your heart, then lie down as the scanner rotates around you taking pictures. A second series of images is taken later on, when the heart is at rest. When comparing the two sets of images, doctors look to see whether abnormalities present under stress disappear once the stress has passed. This difference would suggest that the heart muscle is in danger from coronary artery disease. In people with coronary artery disease, ischemia occurs under periods of stress, but not otherwise. Any abnormalities that appear on both sets of images indicate old heart damage, perhaps from an earlier heart attack.

Dr. Steven C. Port, MD
Cardiologist (Heart Specialist)

Nuclear imaging is frequently performed with stress testing, either exercise stress or a drug stress test, to better show exactly where in the heart and how severe a blockage may be.

The majority of stress tests involve exercise, either on a treadmill or bicycle, while an electrocardiogram, which detects low-voltage electrical activity of the heart through electrodes on the chest, is recorded. Symptoms, changes in the electrocardiogram and, occasionally, changes in blood pressure may indicate the presence of a coronary artery blockage. For a significant number of individuals, an exercise test is not possible. For those people, the heart may be stressed by a drug.

Once the stress portion of the test is completed, images of the heart are taken using a special device called a gamma camera. The images are interpreted by specialized physicians with extensive experience in cardiac imaging.

A nuclear stress test includes all the steps of a regular stress test but adds a few extra so your cardiologist can see how well blood is flowing to your heart.

Before the scan, a nurse or technician will put sticky electrode patches on your chest, arms and legs, just as with a regular stress test. Wires connect the electrodes to an electrocardiogram (ECG) machine that records your heart rate and rhythm. You will also have a blood pressure cuff wrapped around your arm, and an intravenous needle placed in a vein in your arm or hand, so that a small amount of radioactive tracer, or isotope, can be injected into your bloodstream later in the test.

You will exercise on a treadmill or stationary bicycle until you reach your target heart rate (or, if you cannot exercise hard enough, you will receive a medication that mimics exercise by making your heart beater faster and harder). Your target heart rate is generally determined by your age.

Then, a minute or two before you stop exercising, you will receive an injection of a radioactive tracer. You will then lie on the scanner table, keeping very still. During the scan, a large camera rotates around your body, detecting how much radiotracer has reached each area of your heart and creating images that show blood flow. Areas of the heart with good blood flow will have more radioactive tracer than areas with poor blood flow.

A nuclear stress test also includes a set of images taken while the heart is at rest. Depending on the specific protocol your cardiologist uses, the resting scan may be performed either before you begin exercising or two to four hours afterward.

A computer analyzes all the data and creates color-coded images of the heart. By comparing the images taken at rest with those taken immediately after “stress,” your cardiologist can tell which areas of the heart are not getting enough blood and oxygen. This helps to identify which arteries may be narrowed with cholesterol plaque. The scan will also show any areas of the heart that have been permanently damaged by a heart attack.

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