Flail subaortic membrane mimicking left ventricular outflow tract obstruction in hypertrophic cardiomyopathy

Abstract

A subaortic membrane is an uncommon cause for left ventricular outflow tract obstruction. Hypertrophic cardiomyopathy with dynamic left ventricular outflow tract obstruction would mask the presence of the subaortic membrane on transthoracic echocardiography and cause a false diagnosis. We report a patient with subaortic stenosis due to flail subaortic membrane misdiagnosed as obstructive hypertrophic cardiomyopathy on transthoracic echocardiography, identified on transesophageal echocardiography and cardiac catheterization.

Keywords: Hypertrophic cardiomyopathy; Subaortic membrane; Transesophageal echocardiography.

Fig. 1

Precordial leads of electrocardiogram show left ventricular hypertrophy in voltage criteria rather than deep T wave showing in hypertrophic cardiomyopathy (A). Chest radiography shows marked cardiomegaly with pulmonary edema (B).

Fig. 2

Left ventricular (LV) interventricular septal wall thickness and LV posterior wall thickness were 15 mm and 10 mm on parasternal long axis view at diastolic phase and papillary muscle was hypertrophied (arrow) (A). Color Doppler of 2D echocardiography shows flow acceleration at the left ventricular outflow tract (LVOT) level of interventricular septum (B and C). Continuous wave Doppler spectrum was not late peaking appearance but symmetrical appearance and the velocity was increased up to 6 m/sec at the LVOT level during resting state (D).

Fig. 3

One hundred and five degree color compared view of transesophageal echocardiography shows the linear mobile subaortic membrane on basal interventricular septum (arrow). The subaortic membrane disturbs the forward flow toward ascending aorta.

Fig. 4

(A) Double pressure tracing was performed using radial sheath and coronary catheter in left ventricle. (B) Aortic pressure curve was recorded at the ascending aorta level. There is notch on systolic phase of pressure curve (arrow). (C) Aortic pressure curve was recorded and left ventricle pressure curve was recorded at the left ventricular outflow tract (LVOT) level. There was pressure drop during systolic phase on pressure curve recorded at the LVOT level (arrow). The pressure drop was caused by dynamic motion of subaortic membrane during cardiac cycle. The pressure drop is consistent with the notch of ascending aorta pressure curve of Fig. 4B.