Right Ventricular Outflow Tract Obstruction

Definition, Clinical Features, Natural HistoryTop

Right ventricular outflow tract obstruction may be caused by defects of the pulmonary valve, adjacent parts of the right ventricle, and main pulmonary artery that cause obstruction of the outflow of blood from the right ventricle.

1. Classification:

1) Valvular obstruction: The most common type; usually involves an isolated defect, often as a feature of congenital rubella syndrome, component of the tetralogy of Fallot, Noonan syndrome, or Alagille syndrome. Acquired pulmonary stenosis can occur in the setting of carcinoid syndrome.

2) Subvalvular obstruction: Usually a part of complex defects, most commonly associated with ventricular septal defect, tetralogy of Fallot, and subvalvular aortic stenosis.

3) Supravalvular obstruction: Rarely an isolated defect, it may be a part of the tetralogy of Fallot, Noonan syndrome, Williams syndrome, and Alagille syndrome.

2. Symptoms: In moderate and severe stenosis, fatigue, dyspnea, chest pain, and syncope are the common presenting features. Patients can also present with palpitations related to underlying atrial arrhythmias.

3. Signs: In cases of severe stenosis, the jugular venous pressure reveals an augmented a wave. A prominent right ventricular impulse is often palpable in individuals with significant right ventricular outflow tract obstruction. On auscultation, there is an ejection murmur best audible in the second intercostal space at the left sternal border and accompanied by a thrill in many patients with hemodynamically important stenosis. There is a normal first heart sound, wide splitting (not fixed) of the second heart sound with a soft pulmonary component (in severe stenosis), and systolic ejection click that fades during inspiration (in patients with thin and mobile valve leaflets; rarely in supravalvular or subvalvular stenosis). A right-sided S4 sound is audible in patients with a noncompliant right ventricle who are in sinus rhythm. In individuals with associated atrial septal defector ventricular septal defect and severe stenosis there may be cyanosis and clubbing present related to right-to-left shunting.

4. Natural history: Moderate or severe pulmonary stenosis is usually progressive; in milder forms, progression is rare in adults. Subvalvular or supravalvular stenosis causes right ventricular hypertrophy and increasing pressure gradients.

DiagnosisTop

Diagnosis is mainly based on echocardiography, while differential diagnosis includes the individual morphologic forms of the disease. Echocardiography can also provide the level of obstruction(s) and presence of associated congenital defects. A measure of the severity of stenosis is the peak pressure gradient between the right ventricle and the main pulmonary artery:

1) Mild: <36 mm Hg.

2) Moderate: 36 to 64 mm Hg.

3) Severe: >64 mm Hg.

TreatmentTop

Right ventricular outflow tract obstruction at any level requires invasive treatment if the peak pressure gradient on Doppler imaging is >64 mm Hg (peak flow velocity >4 m/s) and the right ventricular function is normal. In valvular stenosis, percutaneous pulmonary balloon valvotomy is the procedure of choice. In subvalvular and supravalvular stenosis as well as in stenosis with calcified or dysplastic valve, surgical repair is indicated. Other indications for interventional treatment include the presence of significant right-to-left shunting (with cyanosis) through an atrial septal defect (ASD) or ventricular septal defect (VSD), decreasing right ventricular function on serial imaging, and objective evidence of decrease in exercise capacity (reduction in maximal oxygen uptake [VO2 max]). In general, long-term survival rates in patients undergoing valvular stenosis repair are similar to those of the general population. However, individuals with significant pulmonary regurgitation after valvotomy develop symptoms related to progressive right ventricular enlargement.