Echocardiographic observations on the association between mitral valve prolapse and asymmetric septal hypertrophy.

One hundred and ninety consecutive patients with mitral valve prolapse (MVP) were studied by echocardiography. Asymmetric septal hypertrophy (ASH) was noted in 16 patients. Three patients had syncope which was associated with supraventricular arrhythmias. Three others had episodes of presyncope which were not related to rhythm disturbances. One of the patients with MVP and ASH had a family history of idiopathic hypertrophic subaortic stenosis. The septal thickness ranged from 1.6 to 3.1 cm, mean = 2 cm. The posterior wall thickness ranged from 0.7 to 2.1 cm, mean = 1.0 cm. The ratio of the thickness of the interventricular septum to that of the posterior wall ranged from 1.5 to 2.5, mean = 1.9. The percentage of thickening of the septum in systole was reduced in 13 patients. The excursion of the interventricular septum was reduced in three patients. In nine patients the left ventricular end-systolic dimension was below the lower limit of normal. Percentage fractional shortening of the left ventricle was increased in eight patients. Since MVP predisposes to cardiac arrhythmias which are poorly toletated in the setting of ventricular hypertrophy and reduced left ventricular compliance, the recognition of this combination of MVP and ASH is of clinical importance.