Regression of myocardial hypertrophy: III. Alterations in left ventricular performance

Abstract

Parameters of left ventricular function were measured during the regression of pressure-overload induced left ventricular hypertrophy. Supravalvar aortic stenosis was produced in rats by constricting their ascending aorta with a metal band. Sham operated rats served as controls. Four weeks after constriction the bands were removed from a group of rats. Other rats with aortic constriction and sham operated controls underwent a sham operation. Two, 4 or 8 weeks later rats from each group underwent a hemodynamic study in situ. The left ventricular-aortic gradient was completely abolished upon removal of the band. Left ventricular weight rapidly decreased toward that of the sham operated control within the first 2 weeks. Cardiac output and stroke volume were similar in the control and banded animals. However, in the debanded animals both parameters fell below the levels of the sham operated control rats and the rats with continued aortic constriction by 2 weeks. By 8 weeks cardiac output and stroke volume in these rats returned to normal. Peak flow velocity was decreased in both the banded and the debanded rats, but returned to control levels by four weeks after debanding. The data suggest that although a normal cardiac output can be maintained by the hypertrophied, pressure-overloaded myocardium, myocardial pump function diminishes during the early regression of hypertrophy coinciding with the loss of myocardium. Function does recover, however, after a longer period of regression. This phenomenon may be related to an abnormality in the hypertrophied myocardial muscle and to the decreased synthesis of myocardial muscle previously demonstrated during the regression of hypertrophy.