Prognostic Significance of Microvascular Obstruction by Magnetic Resonance Imaging in Patients With Acute Myocardial Infarction

Abstract

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 predicts 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 after 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 (χ 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 (χ 2 =5.17, P <.05). Among those returning for follow-up imaging, the presence of microvascular obstruction was associated with fibrous scar formation (χ 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.