Regional and temporal changes in early structural remodeling following myocardial infarction via semi-automatic image analysis.

Reperfusion therapy, the restoration of blood flow following myocardial infarction, is one of the most effective treatment strategies. Unlike early reperfusion, late reperfusion therapy (LRT) has not been linked to differences in infarct size or collagen density. To evaluate the spatial-temporal effects of LRT, 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, border, and peripheral regions from label-free liquid crystal based polarized light microscopy (PolScope) images taken over 5 days of healing. Brightfield and standard polarized light microscopy images of hematoxylin-eosin or Picrosirius Red stained sections were 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 LRT samples. Temporal patterns in collagen density also indicated LRT 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 LRT samples during the necrotic phase of healing. Together these findings suggest LRT accelerates healing and potentially changes the spatial pattern of provisional matrix deposition during the period the heart is most susceptible to rupture events.