Congenital Pulmonary Stenosis

Definition

Congenital pulmonary stenosis is a cardiac anomaly characterized by an abnormal narrowing of the right ventricular outflow tract, which obstructs blood flow to the pulmonary artery. This condition can affect the pulmonary valve (valvular stenosis), the subvalvular region (infundibular stenosis), or the proximal pulmonary artery (supravalvular stenosis). This congenital heart defect may occur in isolation or in association with other congenital malformations, including:

• Tetralogy of Fallot
• Double outlet right ventricle (DORV)
• Univentricular heart

The severity of the stenosis depends on the degree of obstruction and the pressure gradient between the right ventricle and the pulmonary artery. In the most critical cases, the right ventricle develops compensatory hypertrophy to counteract the increased afterload, potentially progressing to right ventricular failure.

Embryology and Pathogenesis

The development of the right ventricular outflow tract and pulmonary valve occurs between the fourth and eighth week of gestation. Defects in this process can lead to abnormalities in the formation of valve cusps, narrowing of the infundibular region, or anomalies in pulmonary artery development. The main pathogenic mechanisms include:

• Defects in endocardial cushion development: may result in incomplete fusion of the valve cusps, leading to thickened, dysplastic, or immobile leaflets.
• Abnormalities of the conotruncal septum: defects in neural crest cell migration can alter the division of the truncus arteriosus.
• Genetic mutations: Pulmonary stenosis has been associated with pathogenic variants in the JAG1 and NOTCH1 genes, as well as genetic syndromes such as Noonan syndrome, Alagille syndrome, and trisomy 21.

Classification

Congenital pulmonary stenosis can be classified based on the site of obstruction:

• Valvular stenosis: the most common form, due to abnormal fusion of the valve cusps, which become thickened, dysplastic, or immobile.
• Infundibular stenosis: caused by muscular hypertrophy of the right ventricular outflow tract, often associated with Tetralogy of Fallot.
• Supravalvular stenosis: results from abnormal growth of the proximal pulmonary artery or genetic syndromes such as Williams-Beuren syndrome.

Pathophysiology

Narrowing of the right ventricular outflow tract leads to an increased afterload on the right ventricle, resulting in ventricular wall hypertrophy. In advanced cases, this hypertrophy becomes maladaptive, increasing filling pressures and reducing the right ventricle's ability to maintain adequate cardiac output. The main hemodynamic consequences include:

• Increased right ventricular pressure: leading to concentric right ventricular hypertrophy.
• Reduced pulmonary blood flow: potentially causing hypoxemia in cases of right-to-left shunting (e.g., in the presence of a patent foramen ovale).
• Right ventricular diastolic dysfunction: possibly impairing left ventricular filling due to ventricular interdependence.

Clinical Manifestations

Symptoms vary depending on the severity of stenosis. Mild cases may be asymptomatic and diagnosed incidentally due to an ejection systolic murmur detected on auscultation. Moderate cases may present with fatigue, exertional dyspnea, and palpitations. Severe cases in neonates with critical stenosis may result in cyanosis, tachypnea, feeding difficulties, and early right heart failure.

Diagnosis

The diagnosis of congenital pulmonary stenosis relies on cardiovascular imaging studies. Doppler echocardiography is the first-line diagnostic tool, allowing assessment of the pressure gradient across the pulmonary valve and right ventricular function. Cardiac magnetic resonance imaging (CMR) provides a three-dimensional evaluation of the right ventricular outflow tract and associated vascular anomalies. Cardiac catheterization with angiography is reserved for complex cases or candidates for percutaneous interventions.

Treatment

Therapeutic management varies based on the severity of obstruction:

• Clinical monitoring: recommended for asymptomatic patients with mild stenosis.
• Balloon valvuloplasty: the treatment of choice for moderate-to-severe valvular stenosis, with high success rates and a low risk of complications.
• Surgical correction: in more complex cases (severe infundibular stenosis, associated structural anomalies), valvulotomy or outflow tract reconstruction with a transannular patch may be performed.
• Pulmonary valve replacement: indicated in cases of severe valvular dysplasia that cannot be treated with valvuloplasty or conservative surgery.

Prognosis

The prognosis of congenital pulmonary stenosis is generally favorable for patients treated early. In mild cases, the quality of life is excellent without the need for treatment. For patients undergoing valvuloplasty or surgery, long-term follow-up is essential to monitor the progression of residual pulmonary insufficiency or restenosis.

Conclusion

Congenital pulmonary stenosis ranges from asymptomatic forms to critical stenosis with significant hemodynamic impact. Echocardiography is the reference diagnostic tool, while treatment varies from simple monitoring to percutaneous or surgical correction. Timely management allows for excellent long-term outcomes and a good quality of life for patients.

References
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