Temporal Changes in Infarct Material Properties: An In Vivo Assessment Using Magnetic Resonance Imaging and Finite Element Simulations

Abstract

Infarct expansion initiates and sustains adverse left ventricular (LV) remodeling after myocardial infarction (MI) and is influenced by temporal changes in infarct material properties. Data from exvivo biaxial extension testing support this hypothesis; however, infarct material properties have never been measured invivo. The goal of the current study was to serially quantify the invivo material properties and fiber orientation of infarcted myocardium over a 12-week period in a porcine model ofMI. A combination of magnetic resonance imaging (MRI), catheterization, finite element modeling, and numeric optimization was used to analyze posterolateral MI. Specifically, properties were determined by minimizing the difference between invivo strains and volume calculated from MRI and strains and volume predicted by finite element modeling. In 1 week after MI, the infarct region was found to be approximately 20 times stiffer than normal diastolic myocardium. Over the course of 12 weeks, the infarct region became progressively less stiff as the LV dilated andejection fraction decreased. The infarct thinned by nearly half during the remodeling period, and infarct fiberangles became more circumferentially oriented. The results reported here are consistent with previously described exvivo biaxial extension studiesof infarct material properties and the circumferential change of collagen orientation in posterolateral infarcts. The current study represents a significant advance in that the method used allows for the serial assessment of an individual infarct invivo over time and avoids the inherent limitations related to the testing of excised tissues.