described for treatment of supravalvar aortic stenosis.165–167 However, due to risk for injury to the aortic valve and coronary arteries, surgical intervention is preferred The goal of surgical intervention is to achieve a symmetric enlargement of the aortic root and other narrowed segments of the aorta and head vessels (Video 44.14 and 44.15).168 Concomitant stenosis of central pulmonary artery and/or coronary arteries should also be addressed during the procedure if indicated Aortic valve repair may also be required Long-Term Outcomes Severe generalized arterial forms and associated aortic valve disease are correlated with late death and the need for reoperation The long-term survival rate is between 70% and 97%, and freedom from reoperation is approximately 65% at 20 years Reoperations are more often due to aortic valve problems than progressive supravalvar aortic stenosis Reoperation also appears more common in nonsyndromic forms compared with patients with Williams-Beuren syndrome.160 However, quality of life is generally good, with the majority of patients in the New York Heart Association functional class I.169–172 Subvalvar Aortic Stenosis Subvalvar stenosis is an obstruction of the left ventricular outflow tract below the aortic valve Congenital subvalvar aortic stenosis is the second most common form of left ventricular outflow tract obstruction and accounts for 15% of all cases.173 There is a male predominance with a male-to-female ratio between 1.5:1 and 2.5:1.174 The genetic basis for subvalvar aortic stenosis is not well defined, although there have been reported familial cases These few reported cases of familial subvalvar stenosis were consistent with an autosomal recessive inheritance, but other pedigrees are suggestive of an autosomal dominant pattern.175–177 Compared with valvar and supravalvar stenosis, the genetic factors in subvalvar aortic stenosis is far less determined Pathophysiology The most common forms or subaortic stenosis are either a fixed obstruction due to a discrete fibrous membrane or a diffuse tunnel-like obstruction This condition may occur in patients with associated congenital heart diseases, including ventricular septal defect, coarctation of the aorta, interrupted aortic arch, and atrioventricular septal defect The lesion may develop in patients with these defects before surgery but may also appear and progress significantly after surgical correction of the associated defects Other rare causes of subaortic stenosis include abnormal attachments of the mitral valve, accessory tissue, abnormal insertion of the mitral papillary muscle, abnormal muscular bands within the left ventricular outflow tract, and spaceoccupying lesions in the left ventricular outflow tract Shone syndrome is characterized by a complex of subvalvar aortic stenosis in association with a supravalvar mitral ring, parachute mitral valve, and coarctation of the aorta Hypertrophic obstructive cardiomyopathy is associated with dynamic subvalvar obstruction due to opposition of the anterior leaflet of mitral valve against the hypertrophied ventricular septum As discussed previously with other forms of left ventricular outflow tract obstruction, subvalvar aortic stenosis can result in compensatory left ventricular hypertrophy This increased afterload results in increased left ventricular systolic pressure and wall stress Subvalvar aortic stenosis is generally progressive, but this can be very variable from stable mild stenosis to rapid worsening obstruction.178 Predictors of disease progression include increased gradient at time of diagnosis, the presence of attachments of the subaortic membrane to the mitral valve, aortic valve thickening at diagnosis, and decreased distance of the membrane to the aortic valve.174 In addition, subvalvar aortic stenosis can result in turbulent flow in the subaortic region and interfere with the motion of the aortic valve and result in aortic regurgitation This is an important physiologic consequence and the degree of regurgitation generally progresses over time Clinical Features As with valvar and supravalvar stenosis, symptoms are uncommon with subvalvar stenosis, even when the narrowing is severe These patients typically present with a new systolic murmur This is most commonly a harsh systolic ejection murmur that is heard the loudest at the left mid-sternal border The murmur will often radiate to the carotids and the degree of obstruction will correlate with the intensity of the murmur Similar to supravalvar stenosis, an ejection click will not be heard There may be an early diastolic murmur if complicated by significant aortic regurgitation Investigations Electrocardiogram The electrocardiogram is usually normal, but there may be varying degrees of left ventricular hypertrophy with strain pattern Chest Radiograph This is often normal, although enlargement of left ventricle and left atrium may be present Echocardiography As with other forms of left ventricular outflow tract obstruction, transthoracic echocardiography with Doppler is the preferred imaging modality for the diagnosis of subvalvar aortic stenosis A comprehensive evaluation is fundamental to the diagnosis and planning for surgical intervention The