78: Surgery for Left Ventricular Outflow Tract Obstruction in Children

Epidemiology

• Left ventricular outflow tract obstruction (LVOTO) occurs in 2.8 of 10,000 live births, accounting for 3 to 6 percent of congenital heart defects.

Morphology

• LVOTO is valvar in 50 percent, subvalvar in 25 percent, and supravalvar in 10 percent of cases. Multilevel obstruction is present in 15 percent of cases.

Pathophysiology

• Obstruction at any level causes increased left ventricular systolic pressure and wall stress and consequent left ventricular hypertrophy. Left ventricular hypertrophy produces subendocardial ischemia and diastolic dysfunction. Eventually, myocardial fibrosis occurs with associated left ventricular systolic dysfunction. Low cardiac output, pulmonary edema, and ventricular arrhythmias may occur late and are associated with increased mortality.

Clinical features:

• Neonates with critical valvar aortic stenosis (AS) present with low cardiac output and shock, requiring emergency treatment. Other forms of LVOTO are often asymptomatic and may be detected by the presence of a heart murmur or abnormalities on ECG. Chest pain, dyspnea, and palpitations occur with increased activity as the degree of obstruction worsens. Symptoms at rest occur with long-standing LVOTO.

Diagnosis

• Diagnostic evaluation is performed in children with a characteristic systolic ejection murmur. Echocardiography allows diagnosis and determines the level(s) of obstruction. The left ventricular outflow tract gradient can be estimated with the use of Doppler flow velocity, and ventricular systolic and diastolic function can be assessed. Diagnostic cardiac catheterization is rarely necessary.

Treatment

• Neonates with critical valvar AS and morphology amenable to biventricular repair respond well to percutaneous transcatheter balloon valvotomy. Aortic valve replacement is required in older children. Enlargement of a small annulus may be achieved with the use of Konno aortoventriculoplasty. Options for valve replacement include a bioprosthetic or mechanical prosthesis, or an autograft (Ross procedure), but all have significant disadvantages in the pediatric population. Discrete subaortic membrane is resected via aortotomy, but diffuse tunnel-like narrowing requires a modified Konno procedure. A variety of aortoplasty techniques are available for patients with supravalvar AS.

Outcomes

• Excellent outcomes, with operative mortality of less than 5 percent, are achieved in most patients. Reoperation to upsize valves is expected in pediatric patients with somatic growth after aortic valve replacement or for structural valve deterioration. Discrete subaortic membrane recurs in approximately 15 to 20 percent of patients despite successful initial repair, and is dependent on the preoperative gradient.