Approach Considerations
SVAS produces abnormalities that are evident on electrocardiography (ECG) and chest radiography. These include increased left ventricular voltages from left ventricular hypertrophy. ST and T wave changes may be present if there is coronary involvement. Additionally, if right ventricular outflow tract obstruction is present, there may be voltage criteria for right ventricular hypertrophy. The principal diagnostic test, however, is echocardiography. Cardiac catheterization along with angiography is indicated to evaluate the severity of the lesion and to confirm the coexisting anomalies prior to surgery if they cannot be accurately assessed with other modalities. MRI may be appropriate to evaluate for stenosis of the arch vessels or for better delineation of the anatomy if a catheterization is not being performed.
Go to Imaging in Aortic Stenosis for more complete information on this topic.
Echocardiography
The anatomic diagnosis of SVAS can reliably be made from 2D echocardiography that uses multiple views, including parasternal, apical long-axis, and suprasternal (seen in the image below).
Two-dimensional suprasternal echocardiographic image of supravalvar aortic stenosis. In SVAS with hourglass deformity and diffuse hypoplasia, the diameter of the ascending aorta is smaller than that of the aortic root. In SVAS with fibrous diaphragm, the external ascending aortic diameter is normal, although an echogenic membrane is commonly observed above the sinuses of Valsalva.
Turbulent color flow mapping indicates the site of hemodynamically significant obstruction and can reveal coronary ostial stenosis, the incidence of which is high in SVAS.[13]
Doppler peak gradient overestimates and, therefore, does not predict catheter-measured gradient well in patients with SVAS and may not be reliable in assessing its severity and guiding the need for intervention.[14]
Cardiac Catheterization
A retrograde aortic catheterization with an end-hole catheter can be used to localize the site of obstruction by showing the pressure gradient above the aortic valve on pullback tracing. Blade balloon angioplasty has been effective for associated peripheral pulmonary artery stenosis when conventional balloon angioplasty fails.[15]
Complications include blood vessel rupture, tachyarrhythmias, bradyarrhythmias, and vascular occlusion. Postcatheterization precautions are for hemorrhage, vascular disruption after balloon dilation, pain, nausea and vomiting, and arterial or venous obstruction from thrombosis or spasm.
Cardiac asystole and mortality due to coronary events have been reported during catheterization and during the postprocedure period. Cardiac catheterization should therefore be performed only if clearly indicated and should be done under general anesthesia, which should be undertaken with close supervision and administered by an experienced anesthesiologist.
Chest Radiography
On chest radiography, the cardiac silhouette may be variably increased, and the ascending aorta may be asymmetrically dilated. The presence of both findings indicates hemodynamically significant SVAS.
Electrocardiography
ECG usually reveals left ventricular hypertrophy, depending on the severity of stenosis. ST/T segment changes may be present with involvement of coronary ostia and the coronary arteries. Right ventricular hypertrophy may be present if there is associated right ventricular outflow tract obstruction.
Cineangiography
A biplane left ventriculogram and an aortogram can reveal the morphology of supravalvar narrowing, stenosis of the arch vessels, aortic root abnormalities, and dilated coronary arteries (see the image below). Right ventricular or pulmonary arterial angiography should be performed simultaneously in order to discern the presence of peripheral pulmonary artery stenosis, particularly in Williams syndrome.
Aortogram of a patient with supravalvar aortic stenosis and dilated sinus of Valsalva. Magnetic Resonance Imaging
Although magnetic resonance imaging (MRI) can provide high definition of SVAS, obtaining an MRI in infants and young children may require sedation, which carries a risk of sudden death. Therefore, this study should be undertaken with close supervision and administered by an experienced anesthesiologist. MRI may be particularly useful in delineating aortic arch anatomy and evaluating for stenosis of the arch vessels.
Computed Tomography
Multislice computed tomography (CT) scanning with angiography can generate high-resolution images of aortic valve lesions within seconds. However, this test exposes the pediatric patient to radiation.
Histologic Findings
Myocardial hypertrophy, coronary intimal hyperplasia, and atherosclerotic changes can be observed in most cases of SVAS. Subendocardial fibrosis may be present in severe cases of SVAS. Abnormal deposition of elastin in arterial walls of patients with SVAS has been seen, which leads to the increased proliferation of arterial smooth muscle cells, resulting in the formation of hyperplastic intimal lesions.[16]
Genetic Evaluation
Obtain a genetic evaluation for patients with SVAS to confirm the diagnosis of Williams syndrome, which is often associated with SVAS. Molecular diagnosis of Williams syndrome can be made by fluorescent in situ hybridization (FISH) using Williams probe.
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