Fig. (11).

(A) and (B)Histological sections of the right atrial appendage with silver-hematoxylin staining. (A) Dog control group in which little myolysis is observed. (B) Dog stimulated group (atrially paced at 400/min for 3 days) in which the myolysis is much more evident around the nucleus of the myocyte (asterisks). (C), (D) and (E) Transmission electron micrographs of the atrial wall observed in a dog subjected to atrial pacing for 3 days. In (C) note the perinuclear myolysis, perinuclear accumulation of glycogen grains (arrows) and nuclear chromatin dispersion. N, nucleus of the myocyte. Magnification x8000. In (D) disruption of an intercalated disc (between arrows). Magnification x10500. In (E) the mitochondria have different sizes and structural alterations with marked dilatation and disruption of mitochondrial cristae (arrows). Magnification x17500.