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) Valvular obstruction: The most common type; usually involves an isolated defect, often as a feature of the congenital rubella syndrome, component of the tetralogy of Fallot, Noonan syndrome, or Alagille 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.
3. Signs: In cases of severe stenosis, the jugular venous pressure reveals an augmented a wave. 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).
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.
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 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.
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. 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.