What structural abnormality was identified in this patient with left ventricular outflow tract obstruction?

• A. Aortic stenosis due to bicuspid valve
• B. Normal septum
• C. Quite marked asymptomatic septal hypertrophy with inducible LV outflow tract obstruction
• D. Dilated cardiomyopathy with reduced EF

Answer: (C)

Dynamic left ventricular outflow tract obstruction is most characteristic of hypertrophic cardiomyopathy with asymmetric septal hypertrophy. The thickened interventricular septum narrows the outflow tract, and during systole the mitral valve can move toward the septum (systolic anterior motion), further reducing the channel and creating obstruction that can be inducible with stress or provocative maneuvers. This can occur even when the patient has few or no symptoms, matching the description of quite marked asymptomatic septal hypertrophy with inducible obstruction. In contrast, fixed obstruction from a bicuspid aortic valve would be aortic stenosis, not LVOT obstruction from septal hypertrophy; normal septum would not produce obstruction; and dilated cardiomyopathy with reduced EF involves dilation and systolic dysfunction rather than septal thickening causing dynamic LVOT obstruction.