99m Tc-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. Methods and 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.