Assessment of metabolism, sympathetic function, and viability in ischemic myocardium

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To assess the cardiac perfusion, metabolism and sympathetic function in normal and ischemic rats' heart were imaged using perfusion tracers (Tl-201 and Tc-99m tetrofosmin), I-125-(-15-(p-iodophenyl)-3-R,S-metyl pentadecanoic acid (BMIPP), and I-125-metaiodobenzylguanidine (MIBG).In normal rats, both perfusion tracers distributed homogeneously among anterior, septal, lateral, inferior walls and endmyocardial and epicardial layers at 15 minutes after tracer injection. I-125-BMIPP also distributed homogeneously at 15 minutes after tracer injection and showed end to epicardial uptake ratio to be 0.98±0.23. I-125-MIBG distribute homogeneously among all segments but end to epicaldial uptake ratio was 0.95±0.01 at 15 minutes after injection and decreased to 0.80±0.04 at 3 hours after injection.In acute ischemic model, left anterior descending coronary artery was occluded and 5 and 20 minutes later, tetrofosmin and BMIPP were injected. In 5 minutes ischemia perfusion tracer uptake decreased to 0.36±0.08 of non-ischemic myocardium accompanied with similar reduction of BMIPP uptake of 0.34±0.07 of normal area in the center of the ischemic area. However, in peripheral zone of ischemia, BMIPP uptake reduction (0.63±0.08) was relatively mild compared with perfusion abnormality (0.39±0.11), suggesting perfusion metabolic mismatch. In 20 minutes ischemia, similar results were observed.These results suggested that 20 minutes after acute ischemia, myocardial fatty acid uptake was relatively preserved compared with perfusion abnormality, indicating that combined perfusion and metabolic imaging is useful for the evaluation of pathophysiologic diagnosis of acute myocardial ischemia.