FUNCTIONAL IMPLICATIONS OF MYOCARDIAL SCAR STRUCTURE

During healing after myocardial infarction, scar collagen content and stiffness do not correlate. We studied regional mechanics and both are a fraction and orientation of large collagen fibers 3 wk after coronar y ligation in the pig. During passive inflation of isolated, arrested hearts, the scar tissue demonstrated significantly less circumferentia l strain but similar longitudinal and radial deformation in comparison with noninfarcted regions of the same hearts. The observed selective resistance to circumferential deformation was consistent with the find ing that most of the large collagen fibers in the scar were oriented w ithin 30 degrees of the local circumferential axis. Furthermore, data from a previous study indicate that during ventricular systole these s cars resist circumferential stretching, whereas they deform similarly to noninfarcted myocardium in the longitudinal and radial directions. We conclude that large collagen fiber structure is an important determ inant of scar mechanical properties and that scar anisotropy allows th e scar to resist circumferential stretching while deforming compatibly with adjacent noninfarcted myocardium in the longitudinal and radial directions.