Idiopathic ventricular septal hypertrophy causing muscular subaortic stenosis.

D ISCRETE, fixed supravalvular, valvular, and subvalvular forms of aortic stenosis are well recognized clinical entities. In 1957, Brock1 first drew attention to the fact that hypertrophied left ventricular musculature could also lead to obstruction of the left ventrieular outflow tract. He termed this "functional obstruction of the left ventricle" or "acquired aortic subvalvar stenosis." One of three cases reported at that time was believed to have developed the outflow tract obstruction as the result of left ventricular hypertrophy secondary to severe systemic hypertension. Two years later Brock reported an additional three cases of muscular obstruction of the left ventricular outflow tract,2 none of which had previous hypertension. In five of his six reported cases, there was no obvious cause for the left ventricular hypertrophy, and it was evident that previous hypertension was not the principal cause of this new syndrome. Since Brock's original observations a number of reports have appeared,3-11 describing cases of obstruction of the left ventricular outflow tract by hypertrophied muscle, there being no obvious cause for the hypertrophy. Ten different terms have been used to describe this condition.'-"' Of particular interest and importance in considering the cause of this muscular subaortic stenosis is the necropsy study by Teare in 1958,3 entitled "asymmetrical hypertrophy of the heart in young adults." This report described a series of eight cases in which the common feature was massive hypertrophy of