Influence of Transmurality, Infarct Size, and Severe Microvascular Obstruction on Left Ventricular Remodeling and Function After Primary Coronary Angioplasty

Infarct size has been considered an established marker of left ventricular (LV) remodeling. We assessed the predictive value of myocardial/microvascular injury assessed by delayed enhanced magnetic resonance imaging (MRI) on LV remodeling and LV ejection fraction after primary coronary intervention (PCI) compared with peak troponin levels, an established index of myocardial infarct size. We performed MRI in 76 patients with first acute myocardial infarction 6 ± 2 days after successful PCI. Necrosis was judged as transmural when delayed enhancement was extended to ≥75% of LV segment thickness. Severe microvascular obstruction was identified as areas of late hypoenhancement surrounded by delayed enhancement. Infarct size was expressed as an index by dividing the total percentage of delayed enhancement involvement by the number of LV segments. LV end-diastolic volume index and function were quantified by 2-dimensional echocardiography at 6 ± 1 months after acute myocardial infarction. Remodeling was evaluated as a change in LV end-diastolic volume index at follow-up compared with baseline. At univariate analyses, transmural necrosis, severe microvascular obstruction, infarct size, and troponin level were correlated directly with remodeling and inversely with LV function at follow-up (p <0.001). At multiple regression, only transmural necrosis and troponin level remained independent predictors of LV remodeling and function. With respect to troponin, transmural necrosis improved the predictive power of LV remodeling (R2 for change = 0.19) and function (R2 for change = 0.16). In conclusion, in patients with acute myocardial infarction undergoing PCI, the amount of transmural necrosis as assessed by MRI is a major determinant of LV remodeling and function, with significant additional predictive value to infarct size and severe microvascular obstruction.