The Development of Outflow Tract Obstruction of the Left Ventricle in Idiopathic Myocardial Hypertrophy

A patient was found to have unexplained left ventricular and septal hypertrophy at age 11, but no pressure gradient across the left ventricular outflow tract. At age 13, there was a mean ejection gradient of 82 mm. Hg. The patient died suddenly 1 month later. This patient demonstrates the development of muscular subaortic stenosis in idiopathic myocardial hypertrophy with obstruction due to increasing muscular hypertrophy. A second patient with left ventricular hypertrophy secondary to a fixed left ventricular outflow tract obstruction produced by an anomalous insertion of a mitral valve leaflet developed additional obstruction due to septal hypertrophy. We believe that the cases presented establish that "muscular subaortic stenosis" may be the result of ventricular hypertrophy of different etiologies. A schema is presented to assist classification of muscular subaortic stenosis.