Supravalvar aortic stenosis (AS) is the least common form of left ventricular outflow tract (LVOT) obstruction. Among children with congenital AS, supravalvar AS has accounted for 8 to 14 percent of cases.
Anatomy — There are at least two anatomic forms of supravalvar AS. The majority of patients (60 to 75 percent) have an hourglass deformity, consisting of a discrete constriction of a thickened ascending aorta at the superior aspect of the sinuses of Valsalva. More diffuse narrowing for a variable distance along the ascending aorta is seen in 25 to 40 percent.
The major histologic features of the ascending aorta in supravalvar AS are a thickened and dysplastic media with an increased number of hypertrophied smooth muscle cells, increased collagen content, and a paucity of elastic tissue with disorganized elastin fibers. Further support for an abnormality in elastin is the high frequency of supravalvar AS in patients with Williams syndrome, which is due to a mutation in the elastin gene. Supravalvar AS in these patients has been characterized as one manifestation of an elastin arteriopathy. Supravalvular AS is often associated with other cardiovascular anomalies including coronary artery stenosis, coarctation of the aorta, aortic regurgitation, and pulmonary artery stenosis. Of importance the location of the stenosis above the origin of the coronary arteries will subject them to the high systolic pressure present in the left ventricle and outflow tract hence they may dilate excessively. The increased shear stress can lead to coronary diasease at an early age.
Supravalvar AS occurs in four settings:
● It is one of the characteristic findings of Williams syndrome along with unusual elfin facies, short stature, intellectual disability, and hypercalcemia. Williams syndrome is caused by a deletion of the elastin gene on chromosome 7q11.23. Other forms of supravalvar AS are also associated with mutations of the elastin gene.(ref.1)
● A familial form without features of Williams syndrome. It is inherited in an autosomal dominant pattern.
● In sporadic patients without a family history.
●In patients with homozygous familial hypercholesterolemia (FH), a rare autosomal dominant disorder in which supravalvar AS occurs in as many as 44 percent of cases. Supravalvar AS also is seen less frequently in heterozygotes (4 percent in one series). This disorder typically affects adults and rarely is seen in children.(ref. 2)
Diagnosis: The diagnosis of supravalvar AS is confirmed by echocardiography. In practice, an accurate Doppler measurement of the aortic gradient frequently is sufficient to determine which patients are candidates for surgical correction of isolated lesions. Magnetic resonance imaging (MRI) with angiography also provides excellent anatomic detail of supravalvar aortic obstruction, together with associated aortic branch vessel disease, if present. CT angiography is also as good as was illustrated in our case.
Management: Surgery is indicated and is curative. It is advised when the mean peak to peak gradient by catheterization is >50 mm. Hg. By Doppler this translates into a peak gradient of 85 mm. Hg. According to a study by Tani et al. (ref. 3).
1. Congenital supravalvar aortic stenosis: a simple lesion?
Stamm C, Friehs I, Ho SY, Moran AM, Jonas RA, del Nido PJ
Eur J Cardiothorac Surg. 2001;19(2):195.
2. Extent and severity of atherosclerotic involvement of the aortic valve and root in familial hypercholesterolaemia.
Rallidis L, Naoumova RP, Thompson GR, Nihoyannopoulos P
3. Usefulness of Doppler echocardiography to determine the timing of surgery for supravalvar aortic stenosis.
Tani LY, Minich LL, Pagotto LT, Shaddy RE, Am J Cardiol. 2000;86(1):114