Diastolic characteristics and cardiac energetics of isolated hearts exposed to volume and pressure overload.

Abstract

The relation between diastolic dimensions and systolic function was studied in isolated rat hearts exposed to pressure (primary hypertension) and to volume load (hyperthyroidism). The hearts were arrested in diastole and cardiac dimensions analysed. Cardiac function was determined using an anterograde working heart preparation. Both models of cardiac overload produced significant left ventricular hypertrophy, however with different design. One concentric and one eccentric form of left ventricular hypertrophy were found in the spontaneously hypertensive rat obtained from two different breeders. An even more pronounced form of eccentric left ventricular hypertrophy was seen in hyperthyroid rats. The hearts with an eccentric form of hypertrophy had a higher maximal stroke volume when perfused at a high aortic pressure than those with a concentric form. At a low aortic pressure and hence a limited coronary perfusion cardiac performance was diminished in both types of spontaneously hypertensive rats but remained normal in hyperthyroid rats. Furthermore, oxygen consumption was reduced in all hypertrophied hearts compared with non-hypertrophied hearts. These data therefore suggest (a) that hearts having an eccentric type of hypertrophy may be in a more favourable situation, delivering a higher stroke volume for a given degree of myocardial fibre shortening; and (b) that the development of coronary vascular structural changes in spontaneously hypertensive rats, thereby increasing vascular resistance, leads to a decrease in left ventricular function at a low coronary perfusion pressure, whereas no such reduction was observed in hyperthyroid hearts, probably owing to a normal vascular resistance.