Evaluation of "metabolic fingerprints" of myocardial ischemia.

Evaluation of regional function and blood flow are used for describing regional myocardial performance. This approach however yields little if any information on regional substrate metabolism. The latter links function to blood flow. Persistence of metabolism, even though abnormal, may be critical for cell survival in myocardial ischemia. Fatty acid oxidation characteristically declines in ischemia while glycolytic flux may increase or be maintained. These changes can be evaluated with C-11 palmitate and F-18 2-fluoro 2-deoxyglucose (FDG) and leave characteristic "fingerprints" on cross-sectional positron emission tomography (PET) images. Blood flow and C-11 palmitate uptake are segmentally reduced while FDG uptake may be increased relative to flow or when compared to normal myocardium. The latter, a discordance between segmental blood flow and FDG uptake, signifies tissue viability and predicts recovery of segmental function after surgical revascularization. The pattern is more sensitive for detection of viable tissue than conventional techniques. It is also frequently seen in acute myocardial infarction. Segments with this pattern may regain function or not. Those segments that fail to improve function spontaneously may require aggressive treatment which could be decided based upon PET findings. Noninvasive detection of such "fingerprints" of myocardial ischemia by PET aids in establishing the presence of viable tissue and may therefore affect patient management. Development of quantitative criteria will be needed to more accurately predict possible tissue outcome which in turn will more clearly establish the need for more aggressive therapeutic measures in acute and chronic ischemic heart disease.