RIGHT VENTRICULAR OUTFLOW TRACT OBSTRUCTION
Right ventricular outflow tract obstruction can occur at the subinfundibular, infundibular, valavular or supravalvular levels.
Subinfundibular stenosis commonly associated with a ventricle septal defect. It is caused by narrowing between prominent and hypertrophied muscle bands or ridges that separate the hypertrophied, high-pressure inlet and apical portions from a low-pressure, non-hypertrophied and non-obstructive infundibular portion of the right ventricle.
Infundibular stenosis usually occurs in combination with other lesions, particularly ventricle septal defec, tetralogy of fallot,and secondary to valvular pulmonary stenosis (reactive myocardial hypertrophy). At the infundibular level, and to some extent the subinfundibular level, the obstruction tends to be dynamic, meaning that the orifice narrows during systole.
Valvular pulmonary stenosis is usually an isolated lesions. Mainly due to intrinsic wall abnormalities and independent of haemodynamics, dilatation of the pulmonary trunk and the left pulmonary artery may occur, the right pulmonary artery generally being less affected. Most often, there is a typical dome-shaped pulmonary valved wit a narrow central opening but a preserved mobile valve base. A dysplastic pulmonary valve, with poorly mobile cusps and myxomatous thickening, is less common and frequenly part of Noonan syndrome. An hourglass deformity of the pulmonary valve, with bottle-shaped sinuses and stenosis at the comissural ridge of the valve, has also been described. In adults, a stenotic pulmonary valve may calcify late in life.
Supravalvular pulmonary stenosis or pulmonary arterial stenosis is caused by narrowing of the main pulmonary trunk, pulmonary arterial bifurcation, or pulmonary branches. It seldom occurs in isolation, and may occur in tetralogy of Fallot, Williams-Beuren syndrome, Noonan syndrome, Keutel syndrome, congenital rubella syndrome or Allagile syndrome. The stenosis may be located in the main branches or more peripherally. It may be discrete or diffuse (hypoplastic) or there may be frank occlusion, and may occur as single or multiple stenosis. Stenosis may be secondary to previous placement of a pulmonary artery band or at previous shunt site. A diameter stenosis >50% is usually considered to be significant, and would be expected to have pressure gradient and a result in hypertension in the proximal pulmonary arteries.
Clinical presentation and natural hystory:
Adults patient with unoperated may be asymptomatic or they may present with angina, dyspnoea, dizziness or syncope. The degree of obstruction is progressive over time.
Patients with mild to moderate valvular pulmonary stenosis are usually asymptomatic. Mild valvular pulmonary stenosis in unoperated adults is usually not progressive. Moderate pulmonary stenosis can progress at the valvular level (calcification) or at the subvalvular, due to reactive myocardial hypertrophy. Patients with severe stenosis may present with dysnoea and reduced exercise capacity, and have a worse prognosis.
Patients may be asymptomatic or have symptoms of dyspnoea and reduced exercise capacity. They are usually recognized in the context of certain syndromes or referred for suspicion of pulmonary hypertension. Peripheral pulmonary artery stenosis may progress in severity.
Catheter intervention is recommended for patients with valvular pulmonary stenosis with valves which are not dysplastic (balloon valvotomy) and with peripheral pulmonary stenosis.
Surgery is recommended for patients with subinfundibular or infundibular pulmonary stenosis and hypoplastic pulmonary annulus, with dysplastic pulmonary valves.