Assessment of residual coronary stenoses using Tc-99m-N-NOET vasodilator stress imaging to evaluate coronary flow reserve early after coronary reperfusion in a canine model of subendocardial infarction

Reperfusion is often incomplete after recanalization therapy because of the presence of residual coronary stenoses. Detecting mild to moderate stenose s requires assessing coronary flow reserve with vasodilator stress. Tc-99m- (N-ethoxy-N-ethyl-dithiocarbamato)nitrido (N-NOET) is a viability-independe nt flow tracer an thus may be well suited for assessing coronary flow reser ve in the acute phase of reperfusion. Methods: Twelve open-chest dogs under went 60 min of total left anterior descending artery (LAD) occlusion follow ed by either full reperfusion (group 1; n = 4) or reperfusion through a res idual critical stenosis (group 2; n = 8). Tc-99m-N-NOET was given during pe ak vasodilator stress 165 min after reperfusion, and initial and 60-min del ayed images were acquired. Regional blood flow was assessed with radiolabel ed microspheres. Results: Infarct size was similar in both groups (9% +/- 2 % vs. 8% +/- 2% of left ventricle). Both initial (0.61 +/- 0.02 vs. 0.73 +/ - 0.01; P < 0.01) and 60-min (0.67 +/- 0.02 vs. 0.80 +/- 0.01; P < 0.01) de fect count ratios (LAD/left circumflex coronary artery [LCx]) differentiate d between the 2 groups, reflecting the greater diminution in coronary flow reserve in group 2 dogs (LAD/LCx flow ratios = 0.37 <plus/minus> 0.04 vs. 0 .57 +/- 0.09; P < 0.01). Interestingly, coronary flow reserve in the reperf used zone of group 1 was diminished despite the absence of a stenosis. Thus , the difference in Tc-99m-N-NOET uptake between the 2 groups was less than expected. Conclusion: In this canine myocardial infarction model with some coronary flow reserve preservation, Tc-99m-N-NOET imaging can detect resid ual coronary stenoses. However, with more prolonged occlusion resulting in more severe endothelial or microvascular dysfunction, it may be difficult t o distinguish varying degrees of vessel patency using any coronary flow res erve technique.