Abstract 2953: Myocardial Uptake of 7′(Z)-[123I]Iodorotenone During Vasodilator Stress in Dogs with Coronary Stenoses
There is a well recognized need for a new generation of SPECT perfusion tracers with improved myocardial extraction over a wide flow range. 7′(Z)-[123I]Iodorotenone (ZIROT) is a new myocardial perfusion imaging (MPI) agent with excellent myocardial uptake and favorable biodistribution. Our objective was to fully characterize the myocardial ZIROT extraction vs flow relationship during vasodilator stress in a large animal model. Accordingly, the adenosine A2A receptor agonist ATL-146e was infused i.v. (0.3 μg/kg/min) in 5 anesthetized, open-chest dogs with critical LAD stenoses. When LCx flow was maximal, 111 MBq (3mCi) of ZIROT and microspheres were co-injected and the dogs were euthanized 5 min later. The LV was divided into 4 short axis slices for ex vivo imaging followed by gamma well counting of myocardial segments. At the time of ZIROT injection, transmural flow in the stenotic LAD zone was similar to baseline (0.90 ± 0.22 vs 0.87 ± 0.11 ml/min/g, respectively P = NS), whereas normal LCx zone flow increased significantly (3.25 ± 0.51 vs 1.00 ± 0.17 ml/min/g, P<0.05). As shown, myocardial ZIROT extraction tracked regional myocardial blood flow better than either 201thallium or 99mTc-sestamibi in our previous studies using a similar canine model. Furthermore, the ZIROT LAD/LCx activity ratios obtained by ex vivo imaging or gamma well counting (0.42 ± 0.08 and 0.45 ± 0.1 respectively) only slightly underestimated the LAD/LCx microsphere flow ratio (0.32 ± 0.09). The ability of ZIROT to more accurately track blood flow over a wide range makes it a very promising new MPI agent with potential for improved CAD detection and better quantitative estimation of the severity of flow impairment.