Surgery for subvalvar aortic stenosis - resection of discrete subvalvar aortic membrane.

Discrete subvalvar aortic membrane is characterized by a fibromuscular shelf located at the area of aortomitral continuity with the extension toward the interventricular septum. As compared to other congenital heart defects, discrete subvalvar aortic membrane is virtually never recognized in early infancy, but appears to be an 'acquired' lesion, typically seen in patients with a more acute angle between the long axis of the left ventricle and the aorta. This angulation leads to imbalance in shear forces, which causes the proliferation of tissue that forms the membrane. The surgical intervention is considered when the gradient across the left ventricular outflow tract is 30 mmHg or more. Surgery is also advocated in infants and children in the presence of aortic regurgitation even when there is no significant gradient. The circumferential excision of the fibrous ridge with septal myectomy is safe and provides efficient relief of obstruction. Aggressive resection of all structures causing flow turbulence and removal of pathological tissue from the valve leaflets might prevent development or progression of aortic regurgitation and might eliminate the substrate for recurrent obstruction. Nevertheless, recurrence still remains a problem, especially in the presence of a predisposing associated congenital heart defect.