NONINVASIVE ASSESSMENT OF NO-REFLOW PHENOMENON IN A CANINE MODEL OF REPERFUSED INFARCTION BY CONTRAST-ENHANCED MAGNETIC-RESONANCE-IMAGING

The aim of this study was to test whether contrast-enhanced magnetic r esonance (MR) imaging may assess in vivo the severity of the no-reflow phenomenon in a dog model of infarction with 2-hour coronary occlusio n followed by reperfusion (6 hours). Subsecond MR imaging combined wit h intravenous bolus administration of superparamagnetic iron oxide par ticles (SPIO) was performed at the fifth hour of reperfusion. An MR in dex was calculated using the difference of signal-intensity enhancemen t between ischemic and nonischemic zones during the SPIO first pass. D ogs were separated into two groups according to the severity of ischem ia: collateral blood flow in the central ischemic zone at 120 minutes of occlusion (radioactive microsphere technique) <22.5% of the flow in the nonischemic zone (group I) or >22.5% (group II). Mean collateral blood flow during occlusion was lower in group I (11.3% +/- 2.9%, n = 7) than in group II (66.8% +/- 19.8%, n = 6, p < 0.05). Mean infarct s ize was significantly larger in group I (58.6% +/- 4.9% of the area-at -risk, n = 7) than in group II (16.5% +/- 6.5%, n = 6, p < 0.05). For the entire population (n = 13), the infarct size was inversely correla ted to the collateral blood flow (r = -0.64, p = 0.02, standard error of estimate = 0.24). The relative rate of enhancement in ischemic myoc ardium (MR index) was significantly lower in group I (38.1% +/- 10.9%) than in group II (142.8% +/- 32%; p < 0.05). In addition, there was a n inverse relation between the MR index and the infarct size (n = 13, r = -0.69, standard error of estimate = 0.07, p = 0.009). In conclusio n, these data suggest that ultrafast MR images with intravenous bolus administration of SPIO during reperfusion is a valuable new method to assess the no-reflow phenomenon in a dog model of myocardial infarctio n.