Identification of residual viable tissue in chronic ECG Q wave infarcts with positron emission tomography

Although electrocardiographic Q waves have routinely been associated with transmural infarction, even small subendocardial infarctions may result in Q waves. The authors postulated that some chronic Q wave infarct regions might exhibit preserved metabolic activity on postron emission tomography (PET) with N-13 ammonia (NH3) and F-18 deoxyglucose (FDG). Twenty patients with 31 Q wave infarct regions (11 septal, 7 anterior, 3 lateral, and 10 inferoposterior) were studied. PET ischemia was defined as a discordant increase in FDG activity relative to NH3, while PET infarction was defined as a concordant reduction in both FDG and NH3 activity. The observed PET patterns were correlated with regional wall motion as assessed by independent observers on LV gram, 2D echo or radionuclide angiogram. There was a significant difference in wall motion score between regions that were normal on PET and those that were ischemic or infarcted on PET. No difference in wall motion was noted between regions with PET ischemia and PET infarction. Thus, PET reveals residual metabolic activity in a high proportion of Q wave infarct regions (68%) and analysis of wall motion does not allow differentiation between ischemic and infarcted regions