Evidence for true obstruction to left ventricular outflow in obstructive hypertrophic cardiomyopathy (muscular or hypertrophic subaortic stenosis).

In obstructive hypertrophic cardiomyopathy (muscular or hypertrophic subaortic stenosis), there is rapid early systolic ejection through an outflow tract that is narrowed by ventricular septal hypertrophy. This results in Venturi forces acting on the mitral leaflets, which cause mitral leaflet systolic anterior motion. Subsequent mitral leaflet-septal contact results in obstruction to left ventricular outflow and concomitant mitral regurgitation. Evidence is provided that the subaortic pressure gradient in obstructive hypertrophic cardiomyopathy reflects true obstruction to left ventricular outflow. It is important to distinguish this truly obstructive subaortic pressure gradient, due to mitral leaflet-septal contact, from an early systolic impulse gradient, as well as from the intraventricular pressure difference that may be encountered in midventricular obstruction or cavity obliteration.