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

Background: N-Ethoxy-N-ethyl-dithiocarbamato-nitrido-(99m)Tc ((99m)Tc-N-NOET) is a new neutral lipophilic (99m)Tc-labeled myocardial perfusion agent with a high first-pass extraction fraction and delayed redistribution kinetics after transient ischemia comparable to what is observed with (201)Tl. It is unknown whether the uptake of this tracer reflects myocardial viability or just reperfusion flow in the setting of a reperfused myocardial infarction.

Results: In 13 anesthetized open-chest dogs, the left anterior descending coronary artery was occluded for 180 minutes, followed by 180 minutes of reperfusion. (201)Tl and (99m)Tc-N-NOET were injected after either 60 (group 1, n=9) or 175 (group 2, n=4) minutes of reperfusion. Myocardial blood flow was measured by radioactive microspheres, and (201)Tl and (99m)Tc-N-NOET tissue activities were determined by gamma-well counting. Normalized myocardial blood flow in the central infarct zone fell from 0.80+/-0. 03 (SEM) and 0.89+/-0.01 at baseline to 0.18+/-0.04 and 0.13+/-0.02 during the occlusion in groups 1 and 2, respectively. Normalized (201)Tl activity in these segments was 0.39+/-0.04 and 0.43+/-0.04 and reflected myocardial viability rather than reperfusion flow (P<0. 001). Normalized (99m)Tc-N-NOET activity in the same segments was 0. 84+/-0.08 and 0.64+/-0.03, respectively (P<0.01 versus (201)Tl; P=NS versus reperfusion flow) and more accurately reflected reperfusion flow (0.99+/-0.17 and 0.70+/-0.04) than residual viability.

Conclusions: The myocardial uptake of (99m)Tc-N-NOET reflects reperfusion myocardial blood flow and not viability in a canine model of reperfused acute myocardial infarction. The clinical use of early (99m)Tc-N-NOET imaging to assess the success of coronary reperfusion in patients with acute myocardial infarction should be investigated.