Presence of Intramyocardial Fat Tissue in the Right Atrium and Right Ventricle – Postmortem Human Analysis

Fig. 1. (A) Digital photograph of a histologic section of RA open in the open-source imaging software GIMP during the tissue selection process. Only the myocardial layer is selected, and larger artifacts are being subtracted from the selection; (B) a color ‘mask’ is applied in GIMP order to prepare the image for measurement in FIJI.

Fig. 2. Preparation of images for measurement: (A) digital photograph of a section of RV stained with hematoxylin and eosin. Scale bar: 1 mm; (B) the same image after application of a color mask over the myocardial layer (red), while other tissues and empty space were filled with white color; (C) the same image after selecting the fat tissue and application of color masks over perivascular fat tissue area (black) and non-perivascular fat tissue area (green). Everything else was filled with white color; (D) a control image with partially transparent masks where the selection can be checked for major inconsistencies and masks can be adjusted accordingly.

Fig. 3. Image shown in Figure 1 open in FIJI. The image was converted to 8-bit type image and thresholding was enabled for the wand tool, which was used to select the mask area, corresponding to the area of myocardial layer on the original image (yellow lining around the black mask denotes selection).

Fig. 4. A representative section of a sample taken from the RV apex of a 68-year-old subject. Areas of fat tissue (arrows) protruding from the epicardium (asterisk) into the myocardium (arrow head). Fat tissue takes up a significant area in this particular region of myocardial layer. Scale bar: 700 µm.