How is nuclear myocardial scanning performed in the workup of myocardial ischemia?

Updated: Aug 07, 2019
  • Author: Thomas F Heston, MD, FAAFP, FASNC, FACNM; Chief Editor: Eugene C Lin, MD  more...
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Answer

The procedure for nuclear myocardial scanning almost always involves a stress test, a resting scan, and a poststress scan. Patient preparation is the first step of the procedure; preparation includes ensuring that the patient has not had any caffeine for at least 12 hours prior to imaging, in case a dipyridamole stress test is necessary. Usually, fasting for 4 hours before imaging is recommended. [20, 34, 37, 39, 6, 42]

If the purpose of the test is for diagnosing possible CAD, all medications should be withheld before the test. [43] On the other hand, if the purpose of the test is to assess response to therapy, most patients should continue all cardiac medications as usual. Patients with diabetes who require insulin should be monitored on a case-by-case basis. Before the stress test, assessment of the patient's cardiovascular history and physical examination should be performed; baseline vital signs should be evaluated, and a 12-lead ECG should be performed.

In addition to careful history-taking and physical examination, all patients undergoing stress testing must provide written informed consent for the procedure, because it is associated with a complication rate of 1-5 cardiac events per 10,000 patients tested. Approximately 4 out of 10,000 patients tested have a myocardial infarction, and 1 out of 10,000 patients tested die of cardiac causes during the test. Therefore, emergency cardiac equipment and medications must be immediately available.

Complication rates may be slightly less when the patient is undergoing pharmacologic stress instead of exercise stress. Complication rates also appear to be declining slowly as advancements are made in the treatment of acute myocardial infarction. Nonetheless, the risk is definite and real. Although greater regulatory emphasis may be placed on the handling of radionuclides, the risk of the procedure comes from stress testing, not radioactivity.

Several imaging procedures are available. A common protocol is the same-day single-radiopharmaceutical protocol performed by using 8 mCi (370 MBq) of technetium-99m (99mTc) sestamibi for the rest study. This step is followed by the stress test, during which the patient receives an injection of 32 mCi of 99mTc sestamibi at peak exertion. The poststress study is performed by using ECG gating. SPECT imaging is performed for both studies by using a 180° collection. A 64 × 64 matrix with 32 stops is used. The Society of Nuclear Medicine Procedure Guidelines list the procedural protocols in detail.


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