Positron Emission Tomography for the Assessment of Myocardial Viability in Acute Myocardial Infarction

Abstract

With the emergence of therapeutic modalities to re-establish regional blood flow to jeopardized myocardium in patients with acute myocardial infarction, there is increased interest in the pathophysiology of tissue reperfusion [1–4]. Experimental and clinical studies in humans suggest a transition from reversible ischemic injury to necrosis within 3 to 6 hours which indicates the temporal dependence of beneficial effects of thrombolytic therapy [5–8]. However, early spontaneous recanalization and the individual degree of residual collateral blood flow might significantly influence the time course of infarct development [8]. In addition, energy demand during the acute phase also affects the evolution of tissue infarction [9, 10]. Consequently, the assessment of the extent and stage of the infarction process from the time elapsed from onset of symptoms is difficult but crucial in a given patient [11]. Clinical and histologic evidence indicates the presence of a mixture of necrotic and ischemic but viable myocytes even in late stages. The clinically important task is to identify “incomplete necrosis” which would benefit from therapeutic interventions. Evaluation of blood flow and regional function cannot distinguish between viable but “stunned” from necrotic myocardium. Based on experimental studies that have revealed enhanced glucose utilization relative to blood flow in ischemic but viable tissue [12, 13], the purpose of this study is

• a) to assess regional myocardial glucose metabolism in acute myocardial infarction to define the stage of the infarction process, and

• b) to compare regional metabolic activity with the outcome of regional function.