An echocardiographic study of localized subaortic hypertrophy.

A prospective echocardiographic investigation was undertaken to determine the prevalence and significance of localized subaortic hypertrophy in 1000 consecutive patients presenting for a routine echocardiographic examination. Localized septal hypertrophy was diagnosed when the subaortic septum was hypertrophied (greater than 1.4 cm) and was 50% thicker than the mid-point of the septum. Patients with hypertrophic cardiomyopathy and fixed subvalvular aortic stenosis were excluded. Eight cases of localized subaortic hypertrophy were identified. In 7 the appearances of the left side of the interventricular septum were similar with an apparently sigmoid shape (reversed S on its side) and in 1 with associated mitral stenosis the septum was a tapered wedge. All patients with localized subaortic hypertrophy had left ventricular hypertrophy (left ventricular mass or posterior wall thickness greater than 2 SD from normal) with a normal size cavity due to aortic valve disease (2 patients were also hypertensive). Of the 180 patients with aortic valve disease, localized subaortic hypertrophy was found in 10% of those with left ventricular hypertrophy and 33% of those with asymmetrical septal hypertrophy (septum to posterior wall ratio of greater than 1.5:1). There was no evidence of subaortic stenosis by pulsed and continuous wave doppler echocardiography (8 cases) and cardiac catheterization (6 cases). The aetiology of this discrete localized muscular bulge is unclear but is presumably due to change in shape of the septum with left ventricular hypertrophy. However, this finding has important implications as a cause of asymmetrical septal hypertrophy and because of the possible false diagnosis of subvalvular stenosis and its effect on ultrasound measurements.