Endocardium of the left ventricle in volume-loaded canine heart. A histological and ultrastructural study

To investigate the effects of volume loading of the heart, the endocardium was studied histologically and ultrastructurally. Thirteen adult female beagle dogs were used. An arterio-venous shunt was constructed between the right common carotid artery and the right external jugular vein in nine animals to induce a volume load. Four animals were used as controls. All were kept for 6-12 months. Heart weight, relative heart weight (heart weight/body weight), cardiac output index, stroke volume index and volumes of both ventricles in the experimental animals were significantly larger than in the controls. Shunted blood volume was significantly correlated with heart weight. The endocardium of the left ventricle in the experimental animals showed elastofibrosis and was significantly thicker than in the controls. In 5 hearts, it was more than 20 microns thick and its endothelial cells showed many long microvilli with a very thick basement membrane (1.5-2.0 microns). The thickness of the endocardium was significantly correlated with the heart weight, relative heart weight and cardiac output index, within 1%, 5% and 5% risk, respectively. These endocardial changes were thought to be induced by hemodynamic changes in the left ventricle of the volume-loaded heart, probably being correlated with changes in cardiac function and morphology.