Which findings on gated myocardial perfusion single-photon emission computed tomography (SPECT) are characteristic 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

Answer

Myocardial wall motion is assessed at the computer monitor. Although the computer calculates an ejection fraction, visually verifying whether the calculated value is reasonable is essential. Occasionally, the calculated ejection fraction value is affected by overlapping liver activity or poor contour tracking, which can make computer-generated values inaccurate. Usually, wall motion is assessed by viewing the inner myocardial wall. A mesh grid is also displayed, which statically shows the end-diastolic image of the myocardial wall. This helps determine wall motion as normal, hypokinetic, akinetic, or dyskinetic (see the video below). Wall motion must be viewed from at least 2 angles to visualize all surfaces. Views from the anterior and lateral angles are common.

This study in a patient with normal findings on myocardial perfusion scanning represents the value of gated imaging in nuclear cardiac scans. The gated images show akinesis of the distal anterior wall along with a reduced left ventricular ejection fraction and an elevated end-systolic volume.

In addition to viewing the wall motion from a 3-dimensional perspective, wall thickening can be visualized by viewing the gated short, vertical long, and horizontal long axes. Polar maps can be helpful in quantifying abnormalities in perfusion, regional ejection fraction, motion, and wall thickening (see the image below); however, abnormalities shown on polar maps must be verified visually.

Polar maps can help identify abnormal findings on Polar maps can help identify abnormal findings on nuclear cardiac images. The polar map shows fairly good end-diastolic perfusion, a decreased regional ejection fraction and motion by the septum, and fairly normal thickening.

On nuclear myocardial scans, a left ventricular ejection fraction greater than 50% is normal. End-systolic volumes greater than 70 mL are considered abnormal, as are end-diastolic volumes greater than 120 mL.


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