Microvascular obstruction (MVO) frequently develops after ST-elevation myocardial infarction (STEMI) and is associated with increased mortality and adverse left ventricular remodeling. We hypothesized that increased extravascular compressive forces in the myocardium that arise from the development of myocardial edema because of ischemia-reperfusion injury would contribute to the development of MVO. We measured MVO, infarct size, and left ventricular mass in patients with STEMI (n = 385) using cardiac MRI 2 to 3 days following successful percutaneous coronary intervention and stenting. MVO was found in 57% of patients with STEMI. The average infarct size was 45 ± 29 g. Patients with MVO had significantly greater infarct size and reduced left ventricular (LV) function (P < 0.01) compared with patients without MVO. Patients with MVO had significantly greater LV mass than patients without MVO and there was a linear increase in MVO with increasing LV mass (P < 0.001). Myocardial edema by T2-weighted imaging increased with increasing LV mass and patients with MVO had significantly greater myocardial edema than patients without MVO (P < 0.01). Patients with MVO had significantly greater left ventricular end-diastolic pressure (LVEDP) than patients without MVO (P < 0.05). In a cohort of patients with STEMI who underwent primary percutaneous intervention, we observed that MVO increased linearly with increasing LV mass and was associated with increased myocardial edema and higher LVEDP. These observations support the concept that extravascular compressive forces in the left ventricle may increase with increasing ischemic injury and contribute to the development of MVO.NEW & NOTEWORTHY Patients with STEMI (n = 385) had cardiac MRIs 2 to 3 days following reperfusion with primary PCI to determine the relationship between myocardial edema, LV mass, and MVO. We observed that MVO increased linearly with LV mass and that myocardial edema measured by T2-imaging also increased linearly with LV mass. Patients with MVO had greater edema and LVEDP than subjects without MVO. These findings suggest that myocardial edema which arises from ischemia-reperfusion injury may result in extravascular compression of the microcirculation manifested as MVO on cardiac MRI.

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