Kinetic analysis of I-125-iodorotenone as a deposited myocardial flow tracer: Comparison with Tc-99m-sestamibi

The goal of this investigation was to assess the accuracy of 7'-Z-[I-125]io dorotenone (I-125-iodorotenone) as a new deposited myocardial flow tracer a nd compare the results with those for Tc-99m-sestamibi. Methods: The kineti cs of these two flow tracers were evaluated in 25 isolated, erythrocyte- an d albumin-perfused rabbit hearts over a flow range relevant to patients. Th e two flow tracers and a vascular reference tracer (I-131-albumin) were int roduced simultaneously as a compact bolus through a port just above the aor tic cannula in the absence of tracer recirculation. Myocardial extraction, retention, washout, and uptake parameters were computed from the venous out flow curves using the multiple-indicator dilution technique and spectral an alysis. Results: The extraction of I-125-iodorotenone was much higher than the extraction of Tc-99m-sestamibi (0.84 +/- 0.05 vs. 0.48 +/- 0.10, respec tively, P < 0.001). I-125-iodorotenone extraction was also less affected by flow than was Tc-99m-sestamibi (P < 0.001). Net retention of I-125-iodorot enone was significantly greater than Tc-99m-sestamibi net retention at 1 mi n (0.77 +/- 0.08 vs. 0.41 +/- 0.11, respectively, P < 0.001) and 26 min (0. 46 +/- 0.13 vs. 0.27 +/- 0.11, respectively, P < 0.001) after tracer inject ion. Flow had less effect on I-125-iodorotenone net retention than on Tc-99 m-sestamibi net retention 1 min after tracer injection (P < 0.04). However, at 26 min, flow had an equivalent effect on the retention of both flow tra cers (P < 0.4). The relationship between I-125-iodorotenone and Tc-99m-sest amibi washout was complex and depended on elapsed time after isotope introd uction and perfusion rate. Reflecting the favorable extraction and retentio n characteristics of I-125-iodorotenone, both its maximum myocardial uptake and its 26-min uptake were more closely related to flow than were those of Tc-99m-sestamibi (P < 0.001 for both comparisons). Conclusion: The extract ion and retention of I-125-iodorotenone were greater than those of Tc-99m-s estamibi, making I-125-iodorotenone the superior flow tracer in the isolate d rabbit heart.