HAeMODYNAMIC ALTERATIONS INDUCED BY ISOPRENALINE IN PATIENTS WITH OBSTRUCTION TO RIGHT VENTRICULAR OUTFLOW

It is now well established that there are two fundamentally distinct types of obstruction to left ventricular outflow, the first resulting from a discrete, fixed narrowing at a valvular, supravalvular, or subvalvular level, and the second being produced by muscular hypertrophy in the left ventricular outflow tract. A number of designations, including obstructive cardiomyopathy (Goodwin et al., 1960) and idiopathic hypertrophic subaortic stenosis (IHSS) (Braunwald et al., 1960) have been applied to the latter condition. In patients with the discrete forms of obstruction to left ventricular outflow, the area of the stenotic outflow orifice remains constant during hemodynamic interven- tions which alter the systolic volume or the contractile state of the ventricle (Braunwald and Ebert, 1962), while with IHSS variations in the severity of obstruction may be induced by a variety ofphysio- logical and pharmacological stimuli. The dimensions of the obstructing orifice are not fixed in IHSS and the size of the left ventricular outflow tract varies, depending upon the contractile state of myocardium, the venous return, the systemic arterial pressure, and the systolic distending pressure