EFFECTS OF ACUTE-ISCHEMIA AND REPERFUSION ON THE MYOCARDIAL KINETICS OF TECHNETIUM 99M-LABELED TETROFOSMIN AND TL-201

Background. Effects of no-flow ischemia and reperfusion on myocardial extraction and retention of Tc-99m-labeled tetrofosmin and (TI)-T-201 were investigated:,, seven isolated, blood-perfused rat hearts with is otope dilution studies at constant coronary perfusion, Methods and Res ults, After a control injection of tracers, no-flow ischemia was induc ed for 20 minutes. After coronary reflow, tracers were injected, Both maximal fractional extraction and capillary permeability-surface area product for tetrofosmin were significantly less than those for (TI)-T- 201 (maximal fractional extraction 0.30 +/- 0.01 and 0.70 +/- 0.09, re spectively, p < 0.001; capillary permeability-surface area product 0.6 6 +/- 0.14 and 2.29 +/- 0.61, respectively, p < 0.001). After no-flow ischemia-reperfusion, both maximal fractional extraction and capillary permeability-surface area product decreased for both tetrofosmin and (TI)-T-201 (decreases in maximal fractional extraction of 23% and 7%, respectively; decreases in capillary permeability-surface area product of 27% and 16%, respectively), although the difference reached statis tical significance only for tetrofosmin, Net extraction at 5 minutes o f both tracers decreased significantly after no-flow ischemia-reperfus ion (tetrofosmin 20% decrease, p < 0.01;(TI)-T-201 23% decrease, p < 0 .02), Early (0 to 5 minutes) washout of tetrofosmin did not change aft er no-now ischemia-reperfusion, whereas the (TI)-T-201 value increased significantly. Although late (5 to 19 minutes) washout of both tracer s increased significantly after no-how ischemia-reperfusion, the myoca rdial clearance rates for tetrofosmin were always significantly less t han those noted for (TI)-T-201. Conclusions. The myocardial uptake of tetrofosmin is depressed (independent of blood how) after severe ische mic injury, apparently resulting mainly from decreased transcapillary exchange, Zn contrast, the depressed uptake of (TI)-T-201 is related m ore to an accelerated early washout from injured myocardium than to a fairly stable initial transcapillary exchange.