Regional and Temporal Changes in Early Structural Remodeling Following Myocardial Infarction via Semi-Automatic Image Analysis.

Reperfusion therapy, the restoration of blood flow following a myocardial infarction (MI), is one of the most effective treatment strategies. Unlike early reperfusion therapy, differences in infarct size or collagen content have not been reported in late reperfusion therapy. To evaluate the spatial-temporal effects of late reperfusion therapy, we conducted multimodal imaging of histologic sections of rat myocardium following permanent coronary artery occlusion or three hours of occlusion. Semi-automatic partitioning identified the infarct core, infarct border, and healthy periphery regions from label-free liquid crystal based polarized light microscopy (PolScope) images taken throughout the first 5 days of healing. Associated brightfield and standard polarized light microscopy images of hematoxylin-eosin or Picrosirius Red stained sections were also used to determine cellular and collagen fiber densities, respectively. Even when we consider multiple definitions for the vulnerable infarct border, its size decreased faster in late reperfusion therapy samples. Temporal patterns in collagen density also indicated late reperfusion led to a more rapid progression through the necrotic phase of healing (when the infarct is vulnerable to rupture) and earlier progression to the fibrotic phase of healing (when the infarct stabilizes). Notably, we also observed a broader region of provisional non-collagenous matrix in late reperfusion samples during the necrotic phase of healing. Together these findings suggest late reperfusion therapy accelerates healing and potentially changes the spatial pattern of provisional matrix deposition during the period the heart is most susceptible to rupture events.