Kinetics of technetium-99m-teboroxime in reperfused nonviable myocardium.

This study evaluates 99mTc-teboroxime uptake and clearance kinetics in reperfused infarcted myocardium.

Methods: In 47 isolated buffer perfused rat hearts, 17 had normal flow (Control), 13 had 30 min of no flow followed by reflow (Noflow30) and 11 had 60 min of no flow followed by reflow (Noflow60). A 1-hr uptake phase was begun by normally perfusing all 41 hearts with 99mTc-teboroxime-doped buffer. After uptake, a 1-hr clearance phase was begun by switching to a 99mTc-teboroxime-free buffer. Technetium-99m activity was monitored with a Nal probe. Triton X-100, a membrane detergent, was given after tracer loading to six additional hearts.

Results: Control and Noflow30 hearts showed near linear and rapid uptake, while Noflow60 hearts showed curvilinear and significantly less uptake than predicted. All three of these groups showed biexponential clearance. Early t1/2 was not significantly different for the three groups (Control = 6.3 +/- 1.9 sem min, Noflow30 = 5.4 +/- 1.3 min, Noflow60 = 8.9 +/- 2.8 min). Late t1/2 was significantly shorter for Noflow30 (52.3 +/- 5.3 min) and the Noflow60 (50.9 +/- 4.3 min), compared to the Control hearts (74.1 +/- 6.6 min, p < 0.05). One-hour fractional clearances were significantly greater for the Noflow30 and Noflow60 hearts (0.65 +/- 0.01 and 0.65 +/- 0.01, respectively) compared to the Controls (0.55 +/- 0.01, p < 0.05). In hearts given Triton X-100, there was a markedly increased fractional clearance of 0.96 +/- 0.01 (p < 0.01 compared to Controls). Electron microscopy showed evidence of mild injury in the Noflow30 hearts, more extensive damage in the Noflow60 hearts and severe irreversible injury in Triton X-100 hearts.

Conclusions: Myocardial 99mTc-teboroxime uptake and clearance kinetics are significantly altered in mildly and moderately injured reperfused myocardium. Technetium-99m-teboroxime clearance is markedly accelerated in the setting of overt damage to cell and organelle membranes induced by Triton X-100.