Analysis of healing after myocardial infarction using polarized light microscopy

To better understand the healing process after permanent coronary artery occlusion in a canine model, the authors used polarized light microscopy. At 6 weeks after occlusion the scar collagen was mainly type I. Some regions of the scar contained a fiber lattice which appeared to be type III collagen. Collagen orientation was measured using a universal stage; subepicardial collagen was obliquely aligned (-14.0 +/- 3.5 degrees), midmyocardial collagen circumferentially aligned (1.4 +/- 0.4 degrees) and subendocardial collagen obliquely aligned (12.7 +/- 2.1 degrees). The molecular organization of scar collagen increased from 1 to 6 weeks after occlusion. Muscle cell disarray, similar to that in hypertrophic cardiomyopathy, was seen in the viable muscle adjacent to the scar. Such abnormal organization extended as far as 1 cm from the edge of the scar. The ability of polarized light microscopy to assess these different parameters from histologic sections demonstrates that it is a useful adjunct to other methods commonly used to study myocardial healing.