Quantification and time course of microvascular obstruction by contrast-enhanced echocardiography and magnetic resonance imaging following acute myocardial infarction and reperfusion

Objectives. We aimed to validate contrast enhanced echocardiography (CE) in the quantification of microvascular obstruction (MO) against magnetic resonance imaging (MRI) and the histopathologic standards of radioactive microspheres and thioflavin-S staining. We also determined the time course of MO at days 2 and 9 after infarction and reperfusion, Background. Postinfarction MO occurs because prolonged ischemia produces microvessel occlusion at the infarct core, preventing adequate reperfusion, Microvascular obstruction expands up to 48 h after reperfusion; the time course beyond 2 days is unknown. Though used to study MO, CE has not been compared with MRI and thioflavin-S, which yield precise visual maps of MO. Methods. Ten closed chest dogs underwent 90 min coronary artery occlusion and reperfusion. Both CE and MRI were performed at 2 and 9 days after reperfusion, The MO regions by both methods were quantified as percent left ventricular (% LV) mass. Radioactive microspheres were injected for blood flow determination. Postmortem, the myocardium was stained with thioflavin-S and 2,3,5-triphenyltetrazolium chloride. Results. Expressed as % total LV, MO by MRI matched in size MO by microspheres using a flow threshold of <40% remote (4.96 +/- 3.52% vs, 5.32 +/- 3.98%, p = NS), For matched LV cross sections, MO by CE matched in size MO hy microspheres using a flow threshold of <60% remote (13.27 +/- 4.31% vs. 13.5 +/- 4.94%, p = NS), Both noninvasive techniques correlated well,vith microspheres (MRI vs. CE, r = 0.87 vs. 0.74; p = NS), Microvascular obstruction by CE corresponded spatially to MRI-hypoenhanced regions and thioflavin-negative regions. For matched LV slices at 9 days after reperfusion, MO measured 12.94 +/- 4.51% by CE, 7.11 +/- 3.68% by MRI and 9.18 +/- 4.32% by thioflavin-S. Compared to thioflavin S, both noninvasive techniques correlated well (CE vs. MRI, r = 0.79 vs. 0.91; D = h'S). Microvascular obstruction size was unchanged at 2 and 9 days (CE: 13.23 +/- 4.11% vs. 12.69 +/- 4.97%; MRI: 5.53 +/- 4.94% vs. 4.68 +/- 3.44%; p = NS for both). Conclusions, Both CE and MRI can quantify MO. Both correlated well with the histopathologic standards. While MRI can detect regions of MO with blood flow <40% of remote, the threshold for MO by CE is <60% remote. The extent of MO is unchanged at 2 and 9 days after reperfusion, (J Am Coll Cardiol 1998:32:1756-64) (C) 1998 by the American College of Cardiology.