Subaortic Stenosis

Excerpt

Subvalvular aortic stenosis (SAS), also called subaortic stenosis, is a rare disorder seen in infants. In most cases, there is a membrane (usually muscular) just below the aortic valve which causes a fixed obstruction to the blood flow across the left ventricular outflow tract. Despite being classified as a congenital heart defect, the fact that it is rare at birth and infancy, its gradual course and its high rate of postoperative recurrence propose that it may be an acquired defect.

Anatomy

The anterior leaflet of the mitral valve along with the intravalvular fibrosa form the posterolateral border and the muscular and membranous portions of the intraventricular septum form the anteromedial borders of the left ventricular outflow tract.

Anatomic Variants

There is a spectrum of variants of subvalvular aortic stenosis that occurs alone or in combination with the others. These are as follows:

1. A thin discrete membrane: The most common lesion

2. A fibromuscular ridge

3. A diffuse fibromuscular tunnel-like narrowing of the left ventricular outflow tract (LVOT),

4. Accessory or anomalous mitral valve tissue

In most patients, membrane attached to the ventricular septum or encompassing the left ventricular outflow tract causes the obstruction.,,. Its position is anywhere from immediately below the aortic valve to further down into the left ventricle. The base of the aortic valve leaflets is noted to be involved by this subaortic tissue thus restricting the mobility and adding to the left ventricular outflow tract.

Natural History

As mentioned previously, the course of subvalvular aortic stenosis is gradual. It is rarely an isolated presentation. SAS is associated with congenital heart defects including a ventricular septal defect, patent ductus arteriosus, coarctation of the aorta, bicuspid aortic valve, abnormal left ventricular papillary muscle, atrioventricular septal defect, among others. In the majority of the patients, SAS is incidentally found when evaluating patients for other congenital heart defects.