Development and determinants of dynamic obstruction to left ventricular outflow in young patients with hypertrophic cardiomyopathy.

BACKGROUNDTo study the development of dynamic subaortic obstruction in young patients with hypertrophic cardiomyopathy (HCM), serial echocardiograms were retrospectively analyzed in a group of 26 consecutive children with this disease who showed no evidence of dynamic outflow obstruction at their initial evaluation (age, 11 +/- 3 years).METHODS AND RESULTSAfter a follow-up of 3-12 years (mean, 7 +/- 3 years), seven of the 26 patients (27%) developed echocardiographic evidence of subaortic obstruction, i.e., marked systolic anterior motion (SAM) of the mitral valve with mitral-septal apposition and increased left ventricular outflow tract systolic velocities (3.8 +/- 0.3 m/sec; range, 3.1-4.5). Patients who developed SAM had smaller transverse dimension of the left ventricular outflow tract and more anteriorly displaced mitral valve when initially evaluated than did patients without development of SAM (outflow tract dimension, 19.1 +/- 4 versus 24.6 +/- 4 mm; mitral valve position index, 1.07 +/- 0.2 versu...