REGIONAL CHANGES IN MYOCYTE STRUCTURE IN MODEL OF CANINE RIGHT ATRIALHYPERTROPHY

To investigate regional variation of myocyte response to atrial hypert rophy, control dogs were compared with dogs with right atrial hypertro phy created by induction of tricuspid regurgitation; after 1 yr, right atrial-to-body weight ratio increased 122% over controls. One section from the interatrial band, appendage and nonappendage roofs, and nona ppendage side of each atrium of each dog was stained to reveal myocyte outlines and transverse tubules; myocyte cross-sectional areas were m easured and transverse tubule prevalence was estimated. In control dog s, interatrial band myocytes were significantly larger and had more tr ansverse tubules than other atrial myocytes. With atrial hypertrophy, right interatrial band myocytes did not increase significantly in size , whereas other right atrial myocytes nearly doubled in size, approach ing the size of interatrial band myocytes without approaching the cont ent of transverse tubules. Left atrial myocytes did not increase in si ze. Thus hypertrophic response of atrial myocytes to hemodynamic stres s depends on the region in which the myocytes are found, and atrial hy pertrophy does not demand transverse tubule proliferation.