MYOCARDIAL KINETICS OF TC-99M TEBOROXIME IN THE PRESENCE OF POSTISCHEMIC INJURY, NECROSIS AND LOW-FLOW REPERFUSION

Objectives. This study evaluated technetium-99m (Tc-99m) teboroxime ki netics in postischemic and partially necrotic myocardium with complete and low flow reperfusion using an isolated perfused rat heart model. Background. Technetium-99m teboroxime has been proposed for use in the early diagnosis of reperfusion after thrombolysis on the basis of mod els of myocardial necrosis with complete reperfusion, Clinically, howe ver, reperfusion is frequently incomplete, resulting in a mixture of n ecrotic, ischemic and postischemic tissue. Methods. Hearts were classi fied into five groups: group 1 (n = 8, control); group 2 (n = 7, 30 mi n of no how with complete reperfusion); group 3 (n = 12, 60 min of no flea to induce partial necrosis, followed by complete reperfusion); gr oup 4 (n = 8, continuous low flow without flow interruption); and grou p 5 (n = 9, 60 min of no flow with low flow reperfusion), Buffer conta ining Tc-99m teboroxime was perfused for 15 min, followed by tracer-fr ee buffer for 35 min, to evaluate uptake and clearance, respectively. Results. Uptake slopes for groups 1 to 5 were (mean +/- SD) 3.0 +/- 0. 7, 2.6 +/- 0.8, 2.1 +/- 0.5, 0.8 +/- 0.2 and 0.8 +/- 0.3, respectively (p less than or equal to 0.0005 for groups 1, 2 and 3 vs. groups 4 an d 5, and p = 0.003 for group 3 vs. groups 1 and 2). Clearance curves f rom groups 1 to 3 were best fit by a biexponential function (p < 0.001 ); those from groups 4 and 5 were monoexponential. In groups 1, 2 and 3, the initial clearance rate constants (k(1)) (0.9 +/- 0.5 x 10(-3); 1.0 +/- 0.2 x 10(-3); 1.1 +/- 0.5 x 10(-3) s(-1), respectively) and th e monoexponential rate constants (k(mono)) (2.0 +/- 0.3 x 10(-4); 2.2 +/- 0.4 x 10(-4); 2.1 +/- 0.2 x 10(-4) s(-1), respectively) were signi ficantly greater than those in groups 4 and 5 (0.9 +/- 0.5 x 10(-4); 1 .2 +/- 0.3 x 10(-4) s(-1), respectively, p less than or equal to 0.005 ). Conclusions. The uptake and initial clearance kinetics of Tc-99m te boroxime depend mainly on myocardial flow in this model, The presence of partial necrosis and postischemic injury has little effect on the i nitial clearance but leads to some reduction in uptake at normal flow rates. Evaluation of Tc-99m teboroxime kinetics may permit early nonin vasive detection of inadequate reperfusion in acute myocardial infarct ion.