Regional changes in hemodynamics and cardiac myocyte size in rats with aortocaval fistulas. 2. Long-term effects.

Regional changes in hemodynamics and cardiac myocyte size were examined in adult rats 5 months after creating a large aortocaval fistula. At that time, cardiac output, left and right ventricular pressures, and left and right ventricular dP/dtmax were measured. Subsequently, isolated cardiac myocytes were collected from the left ventricle, right ventricle, and septum for cell size measurements. Compared with sham-operated controls, percent dry weight was reduced in the liver and kidney but was unchanged in the lung. Heart rate, left ventricular systolic pressure, left ventricular dP/dtmax, and systolic aortic pressure were not changed in rats with fistulas. However, cardiac output, stroke volume, left ventricular end-diastolic pressure, and all measured parameters in the right ventricle were significantly increased. Mean cell volume and the ratio of heart weight to body weight were both elevated 92%. Cell volume, cell length, and cross-sectional area increased significantly in each heart region examined. Hypertrophy was more pronounced in cells from the right ventricle and the endomyocardium of the left ventricle. The percentage of cells with mononucleation or binucleation was not changed in any heart region of rats with fistulas. In summary, despite evidence of renal and hepatic congestion, most indexes of cardiac function were normal or elevated 5 months after creation of a large volume-overload-induced hypertrophy. Data from isolated cardiac myocytes suggested that cellular hypertrophy, rather than hyperplasia, was responsible for the increased cardiac mass.