Development of Left Ventricular Outflow Obstruction in Idiopathic Hypertrophic Subaortic Stenosis

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Abstract
A 70 mm Hg left ventricular outflow obstruction developed in a 15-year-old girl over a period of five years. Initial cardiac catheterization showed the absence of a left ventricular gradient during isoproterenol stimulation. In addition, left-ventricular-function studies revealed a left ventricular mass of 269 g per square meter (normal, 50 to 90 g per square meter), an end-diastolic volume of 66 ml per square meter (normal, 50 to 80 ml per square meter) and an injection fraction of 0.89 (normal, 0.60–0.75). Five years later, after the development of classic findings of idiopathic hypertrophic subaortic stenosis, repeat catheterization demonstrated a 70-mm Hg fixed obstruction across the subaorta area. Left-ventricular-function studies at that time showed an increase in end-diastolic volume to 108 ml per square meter and a decrease in ejection fraction to 0.41.