Effects of acute ischemia and reperfusion on the myocardial kinetics of technetium 99m-labeled tetrofosmin and thallium-201

Abstract

Background. Effects of no-flow ischemia and reperfusion on myocardial extraction and retention of 99mTc-labeled tetrofosmin and 201Tl were investigated in seven isolated, blood-perfused rat hearts with isotope dilution studies at constant coronary perfusion. Methods and Results. After a control injection of tracers, no-flow ischemia was induced 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 201Tl (maximal fractional extraction 0.30 ± 0.01 and 0.70 ± 0.09, respectively, p < 0.001; capillary permeability-surface area product 0.66 ± 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 201Tl (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 statistical significance only for tetrofosmin. Net extraction at 5 minutes of both tracers decreased significantly after no-flow ischemia-reperfusion (tetrofosmin 20% decrease, p < 0.01; 201Tl 23% decrease, p < 0.02). Early (0 to 5 minutes) washout of tetrofosmin did not change after no-flow ischemia-reperfusion, whereas the 201Tl value increased significantly. Although late (5 to 19 minutes) washout of both tracers increased significantly after no-flow ischemia-reperfusion, the myocardial clearance rates for tetrofosmin were always significantly less than those noted for 201Tl. Conclusions. The myocardial uptake of tetrofosmin is depressed (independent of blood flow) after severe ischemic injury, apparently resulting mainly from decreased transcapillary exchange. In contrast, the depressed uptake of 201Tl is related more to an accelerated early washout from injured myocardium than to a fairly stable initial transcapillary exchange.