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Aortic Stenosis, Supravalvar
Updated: Nov 19, 2007
Introduction
Background
Supravalvular aortic stenosis (SVAS) is a fixed form of congenital left ventricular outflow tract (LVOT) obstruction that occurs as a localized or a diffuse narrowing of the ascending aorta beyond the superior margin of the sinuses of Valsalva. It accounts for less than 7% of all fixed forms of congenital LVOT obstructive lesions. SVAS may occur sporadically, as a manifestation of elastin arteriopathy, or as part of Williams syndrome (also known as Williams-Beuren syndrome), a genetic disorder with autosomal dominant inheritance.
Anatomy of subtypes
SVAS has 3 commonly recognized morphologic forms. An external hourglass deformity with a corresponding luminal narrowing of the aorta at a level just distal to the coronary artery ostia is present in 50-75% of patients. In approximately 25% of patients, a fibrous diaphragm is present just distal to the coronary artery ostia. In fewer than 25% of patients, a diffuse narrowing along a variable length of ascending aorta is present. Similarly, the following 3 anatomic subtypes of coronary lesions have been recognized in SVAS:
- Circumferential narrowing of the left coronary ostium
- Ostial obstruction due to fusion of the aortic cusp to the supravalvular ridge
- Diffuse narrowing of the left coronary artery
Pathophysiology
The origins of the coronary arteries proximal to the obstruction site have the same systolic pressure as the left ventricle (LV). Consequently, in time they become dilated and tortuous with hypertrophy and intimal thickening, predisposing them to premature atherosclerosis. The hemodynamic consequences of coronary artery changes are manifested by increased total mean coronary flow but significantly decreased diastolic coronary flow, which is the major determinant of the development of myocardial ischemia. Concentric LV hypertrophy caused by SVAS exacerbates the problem of myocardial ischemia. In most patients, the jet of blood flow from SVAS demonstrates preferential trajectory into brachiocephalic vessels, the so-called Coanda effect; this accounts for a marked increase in the right upper extremity systolic pressure relative to the left.
Natural history
Sudden death can occur in untreated patients with SVAS. However, this appears to be relatively rare overall. Sudden death is more common with Williams syndrome and SVAS with diffuse peripheral pulmonary artery stenosis. The natural history of SVAS is progressive in nature and can be more rapid and severe than in congenital aortic valve stenosis. Sudden death, which can occur in persons of all ages, results from severe LVOT obstruction and coronary artery disease. Severe LVOT obstruction and coronary artery disease may also cause progressive dyspnea upon exertion, angina, and syncope in severe cases and may account for the morbidity in SVAS. Bacterial endocarditis can also cause mortality and morbidity in SVAS.
Frequency
United States
The crude incidence of congenital heart defects is 8.8 per 1000 live births, and SVAS accounts for less than 0.05% of these defects. The sporadic form of SVAS is more common than the autosomal dominant form.
International
The international incidence of SVAS is not clearly known.
Mortality/Morbidity
In one series, the actuarial survival rate following operative repair of SVAS was found to be approximately 85% at 15 years.2 The mortality rate is higher for the diffuse type of SVAS than the localized type. Aortic valve insufficiency can be present in approximately 25% of patients but is usually nonprogressive after surgical relief of SVAS.
Sex
SVAS has no sex predilection.
Age
Patients with SVAS usually become symptomatic during childhood, but SVAS is usually identified during infancy in cases associated with Williams syndrome. The diagnosis of Williams syndrome can be established molecularly based on genetic analysis; therefore, this diagnosis can be made in utero using chorionic villus tissue. Therefore, particularly in patients with Williams syndrome, SVAS can be detected prenatally if it is revealed with fetal echocardiography.
Clinical
History
Symptoms caused by supravalvar aortic stenosis (SVAS) usually develop in childhood and only rarely do so in infancy; however, some patients may develop symptoms in the second or third decade of life.
- Most pediatric patients present because of a heart murmur or the features of Williams syndrome.
- Dyspnea on exertion, angina, and syncope develop in the course of the disease if untreated.
- These symptoms indicate at least a moderate degree of LVOT obstruction.
- Because of the coronary artery involvement, angina may arise early and more often than in other obstructive LVOT lesions.
- Because of the risk of sudden death in SVAS, the development of angina and syncope should prompt immediate investigation.
- Patients with Williams syndrome may additionally develop systemic hypertension and involvement of joints.
Physical
- Asymmetric upper extremities pulses: Discrepancies between carotid pulsations and upper extremities pulses and blood pressure are the characteristic clinical findings of SVAS. The jet of blood flow from SVAS demonstrates preferential trajectory into brachiocephalic (innominate) artery (ie, Coanda effect), which accounts for the discrepancies.
- Precordium: The precordium is usually hyperdynamic, and the apex of the heart is displaced laterally and inferiorly because of ventricular hypertrophy. A thrill in the suprasternal notch is usually felt because of the trajectory of the blood flow jet from SVAS.
- Heart sounds: The first heart sound is generally normal. A narrowly split, single, or paradoxically split second heart sound and a fourth heart sound are present in severe SVAS.
- Heart murmurs: An ejection click is absent in SVAS. The characteristic systolic murmur of SVAS is crescendo-decrescendo in shape, low pitched, and best heard at the base of the heart sited higher than in valvular aortic stenosis. It radiates mainly to the right carotid artery and tends to peak during the last two thirds of the ventricular systole if the obstruction is severe. A high-pitched, short, early diastolic aortic regurgitation murmur is uncommon in SVAS.
Causes
The precise etiology of SVAS is unknown. Its high association with Williams syndrome, in which an elastin gene mutation is present, suggests that defective connective tissue formation contributes to its pathology.
- SVAS may occur sporadically or as part of Williams syndrome, with autosomal dominant inheritance.
- Williams syndrome is a genetic disorder caused by a hemizygous deletion or mutation of the elastin gene at band 7q11.
- Other features of Williams syndrome include elfin facies, mental retardation, outgoing "cocktail party" personality, systemic hypertension, and progressive joint involvement.
- Other cardiovascular anomalies in Williams syndrome consist of multiple stenoses of peripheral pulmonary arteries, stenosis of origins of carotid, coronary and subclavian arteries, and coarctation of aorta.
- The familial form of SVAS caused by an autosomal dominant inheritance but without other features of Williams syndrome is a less common presentation.
- The sporadic form of SVAS is the most common (>50%) presentation. Patients may have associated peripheral pulmonary artery stenosis but show no other features of Williams syndrome.
- The genetic predisposition discussed above is the only known risk factor for acquiring SVAS.
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References
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Further Reading
Keywords
supravalvular aortic stenosis, SVAS, left ventricular outflow tract obstruction, LVOT obstruction, Williams syndrome, Williams-Beuren syndrome, atherosclerosis, myocardial ischemia, Coanda effect, diffuse peripheral pulmonary artery stenosis, congenital aortic valve stenosis, coronary artery disease, bacterial endocarditis, angina, syncope, systemic hypertension, ventricular hypertrophy
