Myocardial kinetics of 201Thallium, 99mTc-tetrofosmin, and 99mTc-sestamibi in an acute ischemia-reperfusion model using isolated rat heart

Objective (201)Thallium (TL), Tc-99m-tetrofosmin (TF), and Tc-99m-sestamibi (MIBI) are extensively used as myocardial perfusion agents. The objective of the present study was to evaluate their kinetics under acute ischemia-reperfusion. Methods Isolated rat hearts, perfused by the Langendorff method at a constant flow rate of 10ml/min, were allotted to normal control, mild ischemia, and severe ischemia groups, in which 20-min tracer wash-in was conducted followed by a 25-min tracer washout. No-flow ischemia (15 min for mild ischemia groups; 30 min for severe ischemia groups) was induced before conducting, wash-in and washout in the ischemia groups. Whole-heart radioactivity was determined with an external gamma detector. Myocardial flow rate (K-1, ml/min) and clearance rate (k(2), min(-1)) were calculated. Results K-ITL, K-ITF, and K-IMIBI decreased according to the severity of ischemia (K-ITL 5.32 +/- 0.53, 4.76 +/- 0.70, and 1.44 +/- 0.59; K-ITF 3.80 +/- 0.70, 2.73 +/- 0.99, and 1.09 +/- 0.45; and K-IMIBI 3.45 +/- 1.10, 2.15 +/- 0.82, and 1.05 +/- 0.13, in the normal control, mild, and severe ischemia groups, respectively). K-1 was significantly higher for TL than for the Tc-99m tracers (P < 0.05), but the Tc-99m tracers had equivalent K-1 values. k(2TL) increased significantly (P < 0.05) in the ischemia groups (k(2TL) 0.062 +/- 0.013, 0.11 +/- 0.045, and 0. 12 +/- 0.035), but showed no significant difference between the ischemia groups. k(2MIBI) and k(2TF) were significantly (P < 0.05) lower than k(2TL) and increased significantly (P < 0.05) in the severe ischemia group (k(2TF) 0.0056 +/- 0.0022, 0.0037 +/- 0.0015, and 0.024 +/- 0.015; and k(2MIBI) 0.00072 +/- 0.0011, 0.00038 +/- 0.00076, and 0.042 +/- 0.034). k(2MIBI) was significantly (P < 0.05) lower than k(2TF) in the normal control and mild ischemia groups. Conclusions Tracer extraction was higher for TL than for the Tc-99m tracers and all tracers decreased according to the severity of ischemia-reperfusion in the three tracer groups. The clearance kinetics of not only MIBI but also TF is possibly useful for the evaluation of the severity of ischemia, and the Langendorff method and a methodological approach by continuous determinations of radioactivity may serve for the quantitative analysis of tracer kinetic profiles.