Quantitative magnetic resonance imaging can distinguish remodeling mechanisms after acute myocardial infarction based on the severity of ischemic insult.

ABSTRACT

The type and extent of myocardial infarction encountered clinically is primarily determined by the severity of the initial ischemic insult. The purpose of the study was to differentiate longitudinal fluctuations in remodeling mechanisms in porcine myocardium following different ischemic insult durations. Animals (N = 8) were subjected to coronary balloon occlusion for either 90 or 45 min, followed by reperfusion. Imaging was performed on a 3 T MRI scanner between day-2 and week-6 postinfarction with edema quantified by T2, hemorrhage by T2*, vasodilatory function by blood-oxygenation-level-dependent T2 alterations and infarction/microvascular obstruction by contrast-enhanced imaging. The 90-min model produced large transmural infarcts with hemorrhage and microvascular obstruction, while the 45 min produced small nontransmural and nonhemorrhagic infarction. In the 90-min group, elevation of end-diastolic-volume, reduced cardiac function, persistence of edema, and prolonged vasodilatory dysfunction were all indicative of adverse remodeling; in contrast, the 45-min group showed no signs of adverse remodeling. The 45- and 90-min porcine models seem to be ideal for representing the low- and high-risk patient groups, respectively, commonly encountered in the clinic. Such in vivo characterization will be a key in predicting functional recovery and may potentially allow evaluation of novel therapies targeted to alleviate ischemic injury and prevent microvascular obstruction/hemorrhage.