Figure 6.

Immunohistochemistry

Immunohistochemistry demonstrates intact desmin (green) in (A) a nonfailing RA compared with a (B) MR LA where there is extensive desmin breakdown and aggregation. There is increased interstitial space in the MR LA in which there are mast cells laden with chymase (pink) and chymase within cardiomyocytes. (C) Giemsa stain shows mast cells (dark purple) in the interstitial space with chymase granules (purple) in the interstitium of extensive collagen surrounding the atrial myocardium (red). (D) There is extensive LA fibrosis (blue) by trichrome stain corresponding to the empty spaces in (B and C) populated by chymase and mast cell granules. (E) There is increased LA collagen by picric acid Sirius red staining and (F) increased collagen relates to a decrease total LA EF. *p < 0.001. Abbreviations as Figures 1 and 4.