LEFT-VENTRICULAR DIASTOLIC FUNCTION OF REMODELED MYOCARDIUM IN DOGS WITH PACING-INDUCED HEART-FAILURE

In patients with heart failure, decreased contractility resulting in h igh end-diastolic pressures and a restrictive pattern of left ventricu lar filling produces a decrease in early diastolic filling, suggesting a stiff ventricle. This study investigated the elastic properties of the myocardium and left ventricular chamber and the ability of the hea rt to utilize elastic recoil to facilitate filling during pacing-induc ed heart failure in the anesthetized dog. Elastic properties of the my ocardium were determined by analyzing the myocardial stress-strain rel ation. Left ventricular chamber properties were determined by analyzin g the pressure-volume relation using a logarithmic approach. Elastic r ecoil was characterized using a computer-controlled mitral valve occlu der to prevent transmitral flow during diastole. We conclude that, dur ing heart failure, the high end-diastolic pressures suggestive of a st iff ventricle are due not to stiffer myocardium but to a ventricle who se chamber compliance characteristics are changed due to geometric rem odeling of the myocardium. The restrictive filling pattern is a result of the ventricle being forced to operate on the stiff portion of the diastolic pressure-volume relation to maintain cardiac output. Slowed relaxation and decreased contractility result in an inability of the h eart to contract to an end-systolic volume below its diastolic equilib rium volume. Thus the left ventricle cannot utilize elastic recoil to facilitate filling during heart failure.