Identification and differentiation of resting myocardial ischemia and infarction in man with positron computed tomography, 18F-labeled fluorodeoxyglucose and N-13 ammonia.

Abstract

Studies have shown that the extraction of glucose per unit flow is increased in moderately ischemic myocardium primarily due to anaerobic glucose metabolism manifested as lactate production, whereas myocardial infarction is characterized by the loss of metabolically active myocardium. To determine the feasibility of demonstrating these metabolic abnormalities reflecting both ischemia and infarction, we used positron computed tomography (PCT) to evaluate relative regional myocardial exogenous glucose utilization and perfusion in 15 patients with recent myocardial infarction. The positron-emitting tracers of glucose metabolism and perfusion, 18F-2-fluoro-2-deoxyglucose (FDG) and N-13 ammonia, respectively, were used. Fourteen of 19 documented infarctions were demonstrated by PCT to have concordantly decreased glucose utilization and perfusion. However, in an additional 11 regions, glucose utilization was disproportionately increased relative to perfusion, consistent with ischemic glucose consumption. These findings correlated with the presence of postinfarction angina, the site of ischemic electrocardiographic changes during chest pain, and the presence of regional left ventricular dysfunction and severe coronary artery disease. Because three ECG infarct zones not detected by PCT demonstrated ischemic glucose utilization, only two of 19 electrocardiographically defined infarctions had no detectable metabolic abnormality. We conclude that the changes in regional FDG and N-13 ammonia concentrations detected with PCT in patients who had had a recent myocardial infarction are consistent with regional exogenous glucose utilization and perfusion in moderately ischemic and irreversibly infarcted myocardium. This approach has the potential to identify and differentiate resting myocardial ischemia from infarction and to assess tissue viability after an ischemic event.