Studies on Digitalis

The acute hemodynamic effects of 0.50 to 0.75 mg. ouabain were studied in six patients with valvular aortic stenosis and in four patients with idiopathic hypertrophic subaortic stenosis. Left atrial and left ventricular pressures were determined by means of transseptal left heart catheterization and cardiac output was measured by the indicator-dilution technic. In the patients with valvular aortic stenosis, ouabain either improved left ventricular function or had no discernible effect on it, but in no patient was left ventricular function depressed. Left ventricular end-diastolic pressure fell slightly or remained unchanged, while cardiac output rose in two of four patients. In the patients with hypertrophic subaortic stenosis, the left ventricular end-diastolic pressure and mean left atrial pressure rose significantly following ouabain administration; cardiac output either fell or remained unchanged and the systolic pressure gradient between the left ventricle and the brachial artery rose. These actions of ouabain in hypertrophic subaortic stenosis are considered to result from a sustained increase in left ventricular contractile force that increased the obstruction produced by the muscular outflow tract.