Structural remodeling of cardiac myocytes in rats with arteriovenous fistulas

Structural changes in the heart associated with chronic volume overloading have not been adequately documented. In anesthetized adult rats, microsurgical techniques were used to produce two types of arteriovenous shunts. The end of a femoral artery was connected to the side of a femoral vein to produce a femoral shunt. Aortocaval fistulas were produced by placing a venous graft (femoral vein) between the abdominal aorta and inferior vena cava. A polyethylene ring was placed around the venous graft to control the size of the shunt. After 10 weeks, rats were anesthetized and hearts were excised, weighed, and perfused with collagenase to obtain isolated myocytes. Heart weight/body weight of rats increased 15% (p less than 0.005) with unilateral femoral fistulas and 41% (p less than 0.001) with aortocaval fistulas. Length of isolated cardiac myocytes was measured directly with a microscope. Cell volume was measured with a Coulter Channelyzer. Myocyte cross-sectional area was calculated from cell volume/cell length. Cell volume increased in proportion to heart weight in each experimental model. With both types of shunts, the majority of myocyte hypertrophy was due to an increase in cell length. There was a trend toward an increase in cross-sectional area in each region of both fistula groups, although this change was not statistically significant. These results indicate that eccentric cardiac hypertrophy was associated with enlargement of individual myocytes primarily as a result of increased length.