Prognostic significance of microvascular obstruction by magnetic resonance imaging in patients with acute myocardial infarction

Background-The extent of microvascular obstruction during acute coronary occlusion may determine the eventual magnitude of myocardial damage and thus, patient prognosis after infarction. By contrast-enhanced MRI, regions of profound microvascular obstruction at the infarct core are hypoenhanced and correspond to greater myocardial damage acutely. We investigated whether profound microvascular obstruction after infarction pr-edicts 2-year cardiovascular morbidity and mortality. Methods and Results-Forty-four patients underwent MRI 10+/-6 days after infarction. Microvascular obstruction was defined as hypoenhancement seen 1 to 2 minutes after contrast injection. Infarct size was assessed as percent left ventricular mass hyperenhanced 5 to 10 minutes alter contrast, Patients were followed clinically for 16+/-5 months. Seventeen patients returned 6 months after infarction for repeat MRI. Patients with microvascular obstruction (n=11) had more cardiovascular events than those without (45% versus 9%; P=.016). In fact, microvascular status predicted occurrence of cardiovascular complications (chi(2)=6.46, P<.01). The risk of adverse events increased with infarct extent (30%, 43%, and 71% for small [n=10], midsized [n=14], and large [n=14] infarcts, P<.05). Even after infarct size was controlled for, the presence of microvascular obstruction remained a prognostic marker of postinfarction complications (chi(2)=5.17, P<.05). Among those returning for follow-up imaging, the presence of microvascular obstruction was associated with fibrous scar formation (chi(2)=10.0, P<.01) and left ventricular remodeling (P<.05). Conclusions-After infarction, MRI-determined microvascular obstruction predicts more frequent cardiovascular complications, In addition, infarct size determined by MRI also relates directly to long-term prognosis in patients with acute myocardial infarction. Moreover, microvascular status remains a strong prognostic marker even after control for infarct size.