Nuclear Medicine / Stress

coronary artery disease (CAD). This test is an effective method of viewing the circulation to the muscles of your heart under both rest and stress conditions. Motion images will also be taken to show the wall motion and efficiency of the left ventricle of your heart. If you are having a treadmill test, your physician can also obtain information regarding your blood pressure response to exercise, any EKG abnormalities, and your conditioning.

A nuclear cardiology stress test consists of 3 parts:

  • A chemically induced test, regular treadmill test or a combination of the two.
  • Imaging of the heart at rest
  • Imaging of the heart after the stress part

The appropriate type of stress test will be decided by your physician or his / her assistant.

The reason this is referred to as a "nuclear" test is because a small amount of a radiopharmaceutical is injected into your vein to tag to the muscles of your heart to be viewed by a gamma camera. If you are having a dual isotope test, thallium-201 and 99mTc sestamibi are used. If you are having a one-day sestamibi or a two day sestamibi test, only the one isotope is used.

When you first come in, a brief medical history will be taken by a technologist or nurse. An intravenous line (IV) will be started. A radioactive dose may be injected and rest images may be done if you having a dual isotope test or a one day Sestamibi test. These images take about 15-20 minutes using a specialized gamma camera. A nurse will then put on EKG leads on your chest to monitor your heart. You will then walk on the treadmill using a standard exercise protocol. Your blood pressure, EKG rhythm and any symptoms you may have will be monitored by the nurse and a cardiologist. When you reach a certain target heart rate or when the cardiologist gives the order, the radioactive agent 99mTc Sestamibi will be injected into the intravenous line and flushed with saline. You will need to continue to walk on the treadmill for another minute to circulate the radioactive material. You will then receive some oral fluids to ensure optimal images. The stress images will be done with the gamma camera. Three EKG patches will be left on your chest and they will be wired up to acquire "gated" images to analyze the wall motion and left ventricular ejection fraction of the heart.

The stress images will be compared to rest images to look at the blood flow to the heart. If a significant blockage is present in your coronary arteries a perfusion defect will show. If there is a defect in the stress but the rest images look normal, this is called ischemia. If there are matching defects in both the stress and rest, an infarction has occurred. If there are no defects then the study is normal.

If good quality images are acquired and the target heart rate is met by the treadmill test, an isotope stress test is capable of detecting significant coronary artery disease approximately 85% of the time. Nearly 10% of patients may have a "false-positive" test, i.e. when the results show a defect where none actually exists. Technical quality problems with the images may occur if a patient is extremely obese, has large breasts, has a prominent diaphragm, or has an EKG with a left bundle branch block.

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