PET reversed mismatch in an experimental model of subacute myocardial infarction

The aim of this study was to evaluate the relationship between flow/metabol ism, histology and functional follow-up in a sheep model of subacute myocar dial infarction, Tn eight juvenile sheep, a myocardial infarction was induc ed by intracoronary injection of macrobeads, Left ventricular function was evaluated using echocardiography. 2-[F-18]fluoro-2-deoxy-D-glucose (18F-FDG )/nitrogen-13-labelled ammonia ((NH3)-N-13) positron emission tomography (P ET) was performed at 6 weeks and 16 weeks after embolization. In five sheep , a dynamic carbon-11 acetate study was performed. In each animal, two regi ons of interest were defined on the polar map, corresponding to the emboliz ed and the non-embolized region. After the final measurements, the hearts w ere processed for histological evaluation. PET revealed a moderately decrea sed flow and oxidative metabolism in the embolized region at 6 weeks, witho ut significant changes at follow-up. At 6 weeks, F-18-FDG uptake in the emb olized area was more severely decreased as compared to the flow index in th e embolized area (P<0.05). At 16 weeks, F-18-FDG metabolism had significant ly recovered (P<0.05). Serial echocardiography showed a persistent decrease in global and regional left ventricular function. Histology revealed a mix of micro-infarcted and viable tissue in the embolized region. In this mode l of subacute myocardial infarction, a PET "reversed mismatch" pattern was observed, with partial recovery of F-18-FDG uptake at follow-up. The histol ogical counterpart of this PET pattern appears to be patchy necrosis.