Four types of congenital aortic stenosis are generally recognized. Valvular stenosis is the most common type; subaortic and supravalvular stenosis and asymmetric septal hypertrophy occur infrequently.
Valvular Aortic Stenosis
Essentials of Diagnosis
Usually asymptomatic in children; angina and syncope indicate severe stenosis. Valvular aortic stenosis accounts for approximately 5% of congenital heart anomalies and is the only type of aortic stenosis that occurs in neonates, accounting for approximately 10% of cases. The clinical characteristics of neonatal critical aortic stenosis differ from those of valvular stenosis in older children in several respects. In neonates, the valve is often unicommissural or bicommissural, and associated anomalies, including other left-sided obstructive lesions, are usually present. Profound clinical deterioration occurs after ductal closure, with left ventricular failure, subendocardial ischemia, and endocardial fibroelastosis. In older children, the valve is more frequently tricommissural, and associated anomalies are less common. Most children are asymptomatic, and symptoms, when present — with the exception of sudden death — typically evolve less acutely.
Children with severe stenosis develop dyspnea, angina, or syncope with effort. Newborns with aortic stenosis have severe heart failure, cyanosis, metabolic acidosis, and associated respiratory distress. In the infant, the cardiac silhouette is usually large, and pulmonary venous congestion is present. Echocardiography provides the essential diagnostic information.
Valvular stenosis cannot be treated medically. In neonates, clinical presentation alone is the indication to intervene in most cases. In older children, indications include a pressure gradient between the left ventricle and aorta of 50 mm Hg or greater; symptoms of syncope, heart failure, and aborted sudden death; and ischemic electrocardiographic changes. Available interventions include various surgical procedures or balloon dilation. In neonates, suitability for restoration of biventricular physiology can be difficult to ascertain. After initiation of prostaglandin therapy for maintenance or restoration of ductal patency, balloon dilation is typically the initial effort to restore biventricular function in neonates. Other surgeons prefer initial surgical valvotomy with the patient supported on cardiopulmonary bypass. The success of either technique ultimately depends on selection of patients appropriate for two-ventricle physiology. For the older child, valve replacement is usually necessary. A variety of replacement options are available, including bioprostheses (stented and unstented porcine and pericardial valves; aortic homografts), pulmonary autografts (Ross procedure), or bileaflet mechanical prostheses.
In general, surgical or balloon valvotomy of a critically stenotic valve in the neonate is not curative. Ultimately, the valve will undergo progressive thickening and stenosis or insufficiency. Mortality ranges between 10% and 40%. Of those surviving, 30–50% will require repeat valvotomy or valve replacement in 5–10 years. Prognosis after valve repair, a preferred option, is substantially better in the older child, with mortality less than 5%. However, long-term confirmation of durability remains unconfirmed. Results are also good with mechanical replacement, with the acknowledgment that issues of growth of the patients as well as structural deterioration of the valve will necessitate eventual valve replacement. The pulmonary autograft is a favored option in children and offers growth potential and freedom from anticoagulation and synthetic surfaces. The pulmonary allograft that is used to replace the harvested autograft remains a source of concern, potentially requiring reintervention when the child is older.
Subaortic congenital stenosis may exist in two forms: discrete and diffuse subaortic stenosis. The discrete form is more common, consisting of a membranous or fibromuscular ring of tissue located beneath the aortic annulus. Other anomalies may coexist, particularly left-sided obstructive lesions (mitral stenosis, aortic coarctation) associated with the diffuse form. The pathophysiology of left ventricular outflow tract obstruction leads to clinical manifestations similar to those of valvular stenosis. The diagnosis is typically confirmed in late childhood and is rare in neonates.
Indications for operative repair include symptoms, a gradient of 50 mm Hg, or evolving aortic regurgitation. Operative repair of the discrete form consists of resection of the membrane, myectomy of the septum. Fifteen-year survival is greater than 95%, with a risk of recurrent obstruction requiring reoperation of 5–20% at 15 years. Repair of the diffuse type requires more extensive modification of the outflow tract, usually with some combination of septal muscle resection, annular and outflow tract enlargement, and in some cases valve replacement, the latter procedures referred to as Konno and Ross-Konno procedures. The operative mortality and the risk of recurrence are greater for the diffuse form of stenosis.
Supravalvular Aortic Stenosis
Isolated supravalvular congenital stenosis is typically in the form of an hourglass-shaped constriction of the aorta at the sinotubular junction (top of the commissures). In fact, obstructive lesions can be found as well in the abdominal aorta (10% of patients) and the pulmonary vasculature or right heart outflow tract (40–70%). This distribution of lesions is due to intrinsically abnormal production of elastin in the media of vessels during development as a consequence of alterations of the elastin gene (7q11.23). It is postulated that decreased elasticity leads to increased shear stresses, leading ultimately to hyperplasia of smooth muscle in the media, with decreased amounts of broken elastin fibers. Therefore, larger arteries, subjected to greater stress, are affected more frequently. Abnormalities of the aortic valve leaflets are present in 20–40% of patients. Less commonly, the left coronary artery may demonstrate various degrees of obstruction.
Supravalvular stenosis is associated with Williams-Beuren syndrome (mental retardation, distinctive facial features, peripheral pulmonary artery stenosis). It occurs in autosomal dominant forms and sporadic forms in which the nonvascular aspects of Williams-Beuren syndrome are absent. The various forms depend on the exact abnormality and mode of acquisition of the altered gene. In general, the dominant symptoms relate to the proximal aortic obstruction.
Various types of operative repairs are available. A synthetic patch can be inserted to widen the area of narrowing. Another approach consists of limited resection of the stenosis, mobilization of the aorta, tailoring the proximal and distal ends for primary anastomosis (no synthetic patch). Both techniques are associated with a low mortality, excellent relief of obstruction. When present, obstruction of the right heart outflow tract or pulmonary vasculature has a tendency to regress with time. For severe lesions, operative repair (patch enlargement) can be conducted at the time of aortic surgery.