Subvalvular aortic stenosis

Aortic Stenosis Microchapters
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Epidemiology and Demographics

Aortic subvalvular stenosis is the second most common form of congenital left ventricular outflow tract obtruction and occurs in 8-30% of all forms of left ventricular outflow tract obstruction. The level of obstruction is located just beneath the aortic valve. HOCM is not present at birth and is not considered a congenital lesion.

The lesion is caused by accumulation of fibrous elastic tissue which most often

Anatomy

There are several varieties of Congenital Aortic Subvalvular Stenosis (or subaortic stenosis):

1. Membranous: A fixed localized membrane 0.5 to 2 cm below the level of the aortic valve and attached to the septum and the base of the anterior mitral leaflet.
2. Fibromuscular:
   • More commonly there is a fibromuscular membrane or tunnel with a significant muscular component which can sometimes be hard to distinguish from IHSS. This is a more severe form and is often associated with a small aortic root.
   • Associated aortic insufficiency (AI) is often present due to the high speed jet of blood through the aortic cusps resulting in fibrosis and retraction.
3. Congenital anomalies of the mitral valve:
   • Attachment to ventricular septum of accessory chordae from anterior mitral leaflet
   • Redundant AV valve tissue causing subaortic obstruction.
4. Aneurysm of the membranous ventricular septum

Clinical Features

• Similar to that of valvular aortic stenosis.
• AI more common in this form (50 to 75% of patients).
• Symptoms begin in infancy or early adulthood.