Tc-99m-N-NOET myocardial uptake reflects myocardial blood flow and not viability in dogs with reperfused acute myocardial infarction

Background-N-Ethoxy-N-ethyl-dithiocarbato-nitrido-Tc-99m(Tc-99m-N-NOET) is a new neutral lipophilic Tc-99m-labeled myocardial perfusion agent with a h igh first-pass extinction fraction and delayed redistribution kinetics afte r transient ischemia comparable to what is observed with Tl-201. It is unkn own whether the uptake of this tracer reflects myocardial viability or just reperfusion flow in the setting of a reperfused myocardial infarction. Methods and Results-In 13 anesthetized open-chest dogs, the left anterior d escending coronary artery was occluded for 180 minutes, followed by 180 min utes of reperfusion. Tl-201 and Tc-99m-N-NOET were injected after either 60 (group 1, n = 9) or 175 (group 2, n = 4) minutes of reperfusion. Myocardia l blood flow was measured by radioactive microspheres, and Tl-201 and Tc-99 m-N-NOET tissue activities were determined by gamma-well counting. Normaliz ed myocardial blood flow in the central infarct zone fell from 0.80 +/- 0.0 3 (SEM) and 0.89 +/- 0.01 at baseline to 0.18 +/- 0.04 and 0.13 +/- 0.02 du ring the occlusion in groups 1 and 2, respectively. Normalized Tl-201 activ ity in these segments was 0.39 +/- 0.04 and 0.43 +/- 0.04 and reflected myo cardial viability rather than reperfusion flow (P<0.001), Normalized Tc-99m -N-NOET activity in the same segments was 0.84 +/- 0.08 and 0.64 +/- 0.03, respectively (P<0.01 versus Tl-201; P=NS versus reperfusion flow) and more accurately reflected reperfusion Row (0.99 +/- 0.17 and 0.70 +/-0.04) than residual viability. Conclusions-The myocardial uptake of Tc-99m-N-NOET reflects reperfusion myo cardial blood now and not viability in a canine model of reperfused acute m yocardial infarction. The clinical use of early Tc-99m-N-NOET imaging to as sess the success of coronary reperfusion in patients with acute myocardial infarction should be investigated.