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RADIOLOGY: HEART: Case# 33669: CARDIAC VIABILITY. The patient is a 47 year old woman with a recent `Q wave myocardial infarction suggesting a transmural defect. The infarct area involved the anterior wall of the left ventricle. A recent cardiac catheterization revealed an ejection fraction (EF) of 20% and severe diffuse coronary stenosis of the proximal LAD. 18-FDG-PET was requested to evaluate for ischemic myocardium that could be salvaged with coronary bypass and subsequently improve the EF. An alternative treatment option was cardiac transplantation. A transmission CT of the chest was first obtained using revolving Ge-68 (a positron emitter) pins as transmission sources. This transmission data was used to correct for non-uniform attenuation encountered within the chest. The patient was then injected with 15 mCi of 15-NH3 IV and imaging begun 3 minutes afterward. The images depict resting perfusion in the left ventricle. The patient was given a glucose load and blood sugars were monitored according to a protocol involving insulin and glucose loading to ensure a blood sugar between 130-160 mg % prior to and after tracer injection. 10 mCi of [18-F] FDG was then injected IV and 30 minutes later PET imaging was performed. The images depict glucose metabolism within the myocardium. Images above are long axis images from the Glucose metabolism study. Images above are long axis images from the perfusion study. Images above are short axis images from the Glucose metabolism study. Images above are short axis images from the perfusion study. Diminished perfusion is noted in the anterior, anteroseptal, and anteroapical walls. However, the glucose metabolism in these areas is relatively greater than the perfusion suggesting viability in the anterior, anteroapical and to a lesser degree in the anteroseptal region. Myocardial viability is a vital factor in estimating the prognostic success of coronary bypass. Normally the myocardium utilizes short-chain fatty acids for metabolism. Ischemic myocardium shifts to glucose metabolism. A relative increase in FDG activity relative to the perfusion in the underperfused areas indicates ischemic (or hibernating) and possibly salvageable myocardium with bypass surgery.

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