Assessment of residual coronary stenoses using 99mTc-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 stenoses requires assessing coronary flow reserve with vasodilator stress. 99mTc-(N-ethoxy-N-ethyl-dithiocarbamato)nitrido (N-NOET) is a viability-independent flow tracer and thus may be well suited for assessing coronary flow reserve in the acute phase of reperfusion.


METHODS
Twelve open-chest dogs underwent 60 min of total left anterior descending artery (LAD) occlusion followed by either full reperfusion (group 1; n = 4) or reperfusion through a residual critical stenosis (group 2; n = 8). 99mTc-N-NOET was given during peak vasodilator stress 165 min after reperfusion, and initial and 60-min delayed images were acquired. Regional blood flow was assessed with radiolabeled 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) defect count ratios (LAD/left circumflex coronary artery [LCx]) differentiated between the 2 groups, reflecting the greater diminution in coronary flow reserve in group 2 dogs (LAD/LCx flow ratios = 0.37 +/- 0.04 vs. 0.57 +/- 0.09; P < 0.01). Interestingly, coronary flow reserve in the reperfused zone of group 1 was diminished despite the absence of a stenosis. Thus, the difference in 99mTc-N-NOET uptake between the 2 groups was less than expected.


CONCLUSIONS
In this canine myocardial infarction model with some coronary flow reserve preservation, 99mTc-N-NOET imaging can detect residual coronary stenoses. However, with more prolonged occlusion resulting in more severe endothelial or microvascular dysfunction, it may be difficult to distinguish varying degrees of vessel patency using any coronary flow reserve technique.
Takehana
K
K
Experimental Cardiology Laboratory, Cardiovascular Division, Department of Medicine, University of Virginia, Charlottesville, Virginia, USA.
Beller
G A
GA
Ruiz
M
M
Petruzella
F D
FD
Watson
D D
DD
Glover
D K
DK
D000704:Analysis of Variance; D000818:Animals; D001783:Blood Flow Velocity; D003326:Coronary Circulation; D003331:Coronary Vessels / Q000000981:diagnostic imaging; D004195:Disease Models, Animal; D004285:Dogs; D015902:Gamma Cameras; D006439:Hemodynamics; D008863:Microspheres; D009203:Myocardial Infarction / Q000000981:diagnostic imaging* / Q000473:pathology; D015425:Myocardial Reperfusion; D015609:Organotechnetium Compounds; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D012039:Regional Blood Flow; D013312:Stress, Physiological / Q000139:chemically induced; D013859:Thiocarbamates
D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; D013859:Thiocarbamates; C093922:technetium Tc 99m, bis(N-ethoxy-N-ethyldithiocarbamato)nitrido-