European Journal of Echocardiography 2008 9(4):569-571; doi:10.1016/j.euje.2007.08.008
Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2008. For permissions please email: journals.permissions@oxfordjournals.org
The vanishing subaortic membrane
Rachel Levine Berger and
Itzhak Kronzon*
NYU Medical Center, Non-Invasive Cardiology Laboratory, 560 First Avenue, New York, NY 10016-6502, USA
Received 9 July 2007; accepted after revision 22 August 2007; online publish-ahead-of-print 1 January 2008.
* Corresponding author. Tel: +1 212 263 5665; fax: +1 212 263 8461. E-mail address: itzhak.kronzon{at}med.nyu.edu
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Abstract
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A fixed subaortic membrane is a rare cause for left ventricular
outflow tract obstruction. This case report describes an unusual
echocardiographic presentation of a subaortic membrane in which
the membrane, initially not seen, was identified only after
a linear shadow posterior to the membrane was seen on a transesophageal
echocardiogram. This represents an unusual demonstration of
an ultrasound beam ‘dropout’ of a subaortic membrane.
Keywords: Subaortic membrane; Shadow artefact
A 71-year-old female with a 5 year history of worsening dyspnea
was referred to our hospital for aortic valve replacement. A
transthoracic echocardiogram performed at the referring institution
demonstrated a thickened but not heavily calcified aortic valve
and a hyperdynamic left ventricle. A transvalvular peak aortic
gradient of 60 mmHg (mean gradient, 35 mmHg) was demonstrated
by continuous wave Doppler imaging. In order to reconcile the
aortic valve appearance and the pressure gradient, the patient
underwent cardiac catheterization at the referring institution
that demonstrated a similar transaortic valve pressure gradient.
Upon arrival, physical examination revealed a 3/6 systolic ejection murmur and bibasilar rales. A repeat transthoracic and transesophageal echocardiogram was performed prior to surgery. The echocardiogram revealed a mildly thickened aortic valve that measured 1.2 cm2 by planimetry. The echocardiogram revealed a high systolic flow velocity in the left ventricular outflow tract (LVOT); however, it was noted that the increased turbulence in the LVOT began proximal to the aortic valve. (Figure 1) The LVOT flow velocity, measured by pulsed Doppler, was increased, aliasing at 2.5 m/s. The peak systolic velocity across the LVOT measured by continuous-wave Doppler imaging was 3.9 m/s (Figure 2). There was mild aortic insufficiency. An unusual linear shadow artefact was noted anterior to the LVOT that appeared at the same level the turbulent flow was noted (Figure 3). Initially, no anatomic subvalvular obstruction could be seen. However, upon closer inspection and changes in the gain and brightness settings, a vague, linear structure could be depicted in the LVOT, just above the linear shadow (Figure 4). This linear shadow artefact was thought to be caused by a fixed subaortic membrane that was not initially seen in the LVOT.
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Figure 1 Transesophageal echocardiography, 121°, demonstrated increased turbulence in the left ventricular outflow tract, beginning proximal to the aortic valve on the transesophageal echocardiogram. LA, left atrium, LVOT, left ventricular outflow tract.
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Figure 3 Transesophageal echocardiogram, 121°, demonstrated a linear shadow anterior to the left ventricular outflow tract at the same level where the turbulent flow was noted (white arrows). There is no clear evidence of anatomic subvalvular obstruction. LA, left atrium; LVOT, left ventricular outflow tract.
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Figure 4 After increasing the gain, a linear structure was vaguely visualized in the LVOT directly posterior (white arrows) to the linear shadow artefact (black arrows). This linear structure was the fixed subaortic membrane that was not initially seen with a normal gain setting. LA, left atrium.
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The patient underwent surgical resection of a thin subaortic
membrane and an aortic valve replacement with significant improvement
in her LVOT gradient. The postoperative mean gradient measured
14 mmHg. The patient's dyspnea resolved and she was discharged
home.
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Discussion
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This patient had the combination of a fixed subvalvular membrane
causing subaortic stenosis and mild to moderate valvular aortic
stenosis.
1,2 This case demonstrates that thin structures which
are positioned parallel to the interrogating ultrasound beam
may ‘drop out’. Most echocardiographers are familiar
with the interatrial septal dropout that may be seen on the
apical four-chamber view and may simulate an atrial septal defect.
However, this is an unusual demonstration of an ultrasound beam
‘drop out’ of a subaortic membrane.
In this case, a thin membrane which created a significant LVOT gradient was not initially seen on transthoracic and transesophageal examination. Instead, it was the findings of flow acceleration and shadowing in front of the membrane that convinced us that an ‘unseen membrane’ was indeed present.3
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References
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- Carr JA, Sugeng L, Weinert L, Jeevanandam V, Lang RM. Images in cardiovascular medicine. Subaortic membrane in the adult. Circulation (2005) 112:e347.[Free Full Text]
- Volpe S, Marrone G, Renda G, Spina R, Gallina S, Marchetti A, et al. Images in cardiovascular medicine. Membrane-type subaortic stenosis in the adult. Italian Heart J (2003) 4:651–2.
- Wu W, Teng J, Tsai LM, Tsai WC, Lin LJ, Li YH., et al. Images in cardiovascular medicine. Unusual manifestation of subaortic membrane. Circulation (1998) 97:605–6.[Free Full Text]
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