Pulmonary stenosis refers to a congenital anomaly involving narrowing between the right ventricle and the pulmonary artery. It may occur as an isolated defect or as part of a complex congenital heart condition.
Pathoanatomy
It can involve infundibular (right ventricular outflow tract) stenosis, pulmonary valve stenosis, and stenosis of the annulus, main pulmonary artery, or its branches. Pulmonary valve stenosis is the most common type, characterized by thickened valve cusps with commissural fusion, leading to a "fish-mouth" appearance that protrudes into the pulmonary artery. Post-stenotic dilatation of the pulmonary trunk is often observed. Infundibular stenosis may present as diaphragmatic or tubular narrowing. Diaphragmatic stenosis occurs when fibromuscular tissue forms a localized constricting ring in the right ventricular outflow tract, dividing the right ventricle into two chambers. The thin-walled chamber between the stenotic ring and the pulmonary valve is known as the "third ventricle." Tubular narrowing involves diffuse thickening of the anterior wall of the right ventricle, the septomarginal trabecula, and the muscular bands, resulting in severe stenosis and hypoxic spells. Stenosis of the main pulmonary artery and its branches may appear as localized or multiple areas of underdevelopment.
Pathophysiology
Pulmonary stenosis causes obstruction to blood flow from the right ventricle to the pulmonary artery. The right ventricle compensates by increasing its contractility and intracavitary pressure to pump blood effectively. Chronic pressure overload leads to right ventricular hypertrophy and reduced right ventricular cavity size, thereby worsening the outflow tract obstruction. Some patients may develop tricuspid regurgitation due to elevated right ventricular pressure and displacement of the papillary muscles. In advanced stages, right ventricular remodeling and fibrosis occur, resulting in reduced myocardial contractility and tricuspid valve incompetence, which may eventually cause heart failure. Impaired venous return and blood stasis may lead to peripheral cyanosis. In severe cases, with coexisting atrial or ventricular septal defects, right-to-left shunting of blood may cause central cyanosis.
The pressure gradient between the right ventricle and the pulmonary artery reflects the degree of stenosis. Normal pressure differences are below 5 mmHg. A gradient between 5 and 40 mmHg indicates mild stenosis, 40 to 100 mmHg indicates moderate stenosis, and gradients above 100 mmHg indicate severe stenosis.
Clinical Presentation
Patients with mild stenosis are often asymptomatic for long periods. Moderate to severe stenosis may present with symptoms such as chest tightness, shortness of breath, palpitations, and syncope after exertion, as well as reduced exercise tolerance and fatigue. Symptoms typically worsen with age. In advanced stages, signs of right heart failure, such as hepatomegaly, lower extremity edema, and ascites, may develop. Auscultation typically reveals a loud ejection systolic murmur at the second intercostal space along the left sternal border, accompanied by a systolic thrill. Pulmonary valve closure may result in a diminished or absent second heart sound. For infundibular stenosis, the murmur is usually heard at the third to fourth intercostal space along the left sternal border. In severe stenosis, the cardiac murmur may lessen in intensity, and cyanosis of the lips and extremities may be observed.
Auxiliary Examinations
Electrocardiogram (ECG)
Findings include right axis deviation, right ventricular hypertrophy with strain patterns, inverted T waves, and peaked P waves.
Chest X-Ray
The pulmonary vasculature may appear reduced, while right atrial and right ventricular enlargement can be observed with a rounded cardiac apex. In valvular stenosis, post-stenotic dilation of the pulmonary artery may cause prominence of the pulmonary artery segment.
Ultrasound: This modality provides highly accurate diagnosis of pulmonary stenosis, identifying the location and severity of the stenosis and estimating the transvalvular pressure gradient.
Diagnosis
Diagnosis is typically established based on clinical symptoms and signs in combination with findings from ECG, chest X-ray, and ultrasound. Right heart catheterization and right ventricular angiography may be performed when necessary. Pulmonary stenosis should be differentiated from atrial septal defect, ventricular septal defect, patent ductus arteriosus, and tetralogy of Fallot.
Treatment
Indications for Surgery
Mild stenosis does not require surgical treatment. Patients with moderate or greater stenosis, clinically significant symptoms, evidence of right ventricular hypertrophy on ECG, or a right ventricular-to-pulmonary artery pressure gradient exceeding 50 mmHg may benefit from elective surgery. In cases of severe stenosis with syncope or secondary right ventricular outflow tract stenosis, early surgical intervention is recommended.
Surgical Techniques
A median sternotomy is used to establish cardiopulmonary bypass, and the procedure may be performed with the heart arrested or beating under direct visualization. Pulmonary valve stenosis is treated via an incision in the pulmonary artery, performing commissurotomy of the valve cusps. For infundibular stenosis, the right ventricular outflow tract is opened to remove the fibromuscular ring and the hypertrophied septomarginal and muscular bands, thereby relieving the obstruction. If the stenosis persists, the outflow tract can be widened with an autologous pericardial or synthetic patch. For annular stenosis, the valve annulus may be incised and widened with a transannular patch extending from the right ventricular outflow tract to the pulmonary artery. In cases of stenosis involving the main pulmonary artery or its branches, patches constructed from pericardium or synthetic materials may be placed at the site of narrowing.
Percutaneous pulmonary balloon valvuloplasty involves advancing a balloon catheter from the femoral vein to the pulmonary valve under fluoroscopic guidance to dilate the stenosed valve, and is suitable for isolated valvular stenosis with mild valvular abnormalities. Surgical transcatheter balloon dilation may be performed through a small incision in the second intercostal space under esophageal ultrasound guidance, involving direct puncture of the right ventricular outflow tract for balloon dilation. This approach is primarily used for small, low-weight, or severely stenosed pediatric patients, offering reduced surgical trauma and faster recovery. However, balloon dilation may be less effective in some cases and may lead to pulmonary regurgitation due to valvular tearing. For older children and adults with isolated stenosis of the main pulmonary artery or its branches, transcatheter placement of stents in the pulmonary artery is an alternative option.