title: Temporal Changes in Infarct Material Properties: An In Vivo Assessment Using Magnetic Resonance Imaging and Finite Element Simulations.
abstract: BACKGROUND
  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 ex vivo biaxial extension testing support this hypothesis; however, infarct material properties have never been measured in vivo. The goal of the current study was to serially quantify the in vivo material properties and fiber orientation of infarcted myocardium over a 12-week period in a porcine model of MI.
  
  
  METHODS
  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 in vivo strains and volume calculated from MRI and strains and volume predicted by finite element modeling.
  
  
  RESULTS
  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 and ejection fraction decreased. The infarct thinned by nearly half during the remodeling period, and infarct fiber angles became more circumferentially oriented.
  
  
  CONCLUSIONS
  The results reported here are consistent with previously described ex vivo biaxial extension studies of 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 in vivo over time and avoids the inherent limitations related to the testing of excised tissues.
authors.affiliation: Gorman Cardiovascular Research Group, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: McGarvey
authors.affiliation: Department of Mechanical Engineering, Lexington, Kentucky.
authors.forename: Dimitri
authors.initials: D
authors.lastname: Mojsejenko
authors.affiliation: Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Shauna M
authors.initials: SM
authors.lastname: Dorsey
authors.affiliation: Department of Mechanical Engineering, Lexington, Kentucky.
authors.forename: Amir
authors.initials: A
authors.lastname: Nikou
authors.affiliation: Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Burdick
authors.affiliation: Gorman Cardiovascular Research Group, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Gorman
authors.affiliation: Department of Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Jackson
authors.affiliation: Gorman Cardiovascular Research Group, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: James J
authors.initials: JJ
authors.lastname: Pilla
authors.affiliation: Gorman Cardiovascular Research Group, University of Pennsylvania, Philadelphia, Pennsylvania; Department of Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Gorman
authors.affiliation: Department of Mechanical Engineering, Lexington, Kentucky; Department of Surgery, University of Kentucky, Lexington, Kentucky. Electronic address: wenk@engr.uky.edu.
authors.forename: Jonathan F
authors.initials: JF
authors.lastname: Wenk
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D020342:Finite Element Analysis; D008279:Magnetic Resonance Imaging; D008297:Male; D009203:Myocardial Infarction / Q000473:pathology*; D013552:Swine; D013997:Time Factors