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

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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.

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