Pulmonary Stenosis and Atresia

Definition

PS refers to a narrowing of the right ventricular outflow tract secondary to a lesion that can occur at any of three levels—valvular, subvalvular, or infundibular region of the pulmonary artery. The most common form is a dysplastic valve with partial fusion of the three pulmonary valve cusps.

PA with intact interventricular septum, also known as hypoplastic right heart syndrome, is characterized by complete blockage of the right ventricular outflow tract. Atresia usually occurs at the level of the valve, and less frequently the pulmonary artery is also atretic. The competence of the tricuspid valve and the presence of tricuspid anomalies determine the development of the right ventricle, but this is usually hypoplastic with a proportionally smaller tricuspid valve. Less commonly, the right ventricle is dilated or of normal size.

Prevalence and Epidemiology

The estimated incidence of PS is approximately 9% to 10% of all congenital heart diseases (CHDs) diagnosed in neonates. PA is diagnosed in 1 : 22,000 live births, and it accounts for 1% to 5% of all prenatally diagnosed CHDs.

Etiology and Pathophysiology

As in most CHDs, the etiologies of PS and PA are multifactorial. The risk of chromosomal anomalies and extracardiac malformations is low; there is a 2% risk of aneuploidy. PS can appear in the context of different nonchromosomal syndromes (e.g., Williams, Alagille, and Noonan syndromes), and it is a typical finding of congenital rubella syndrome.

As with any other CHD, PS can be associated with other CHDs:

• 1.

  Isolated PS is less commonly diagnosed in fetal life because the diagnosis is more challenging, especially in less severe forms.

• 2.

  PS associated with other CHDs, typically with conotruncal anomalies, represents the most common form detected during fetal life.

In PA, the presence of a ventricular septal defect determines another important distinction: pulmonary atresia in association with a ventricular septal defect may be part of tetralogy of Fallot or other CHDs (double-outlet ventricle, transposition of great arteries, heterotaxy syndromes; see Chapter 86, Chapter 87, Chapter 88, Chapter 91 ). The characteristics of the tricuspid valve determine the size of the right ventricle in PA. Two types of PA can be distinguished in relation to the tricuspid valve:

• 1.

  PA type I (75% of cases): there is a competent or atretic tricuspid valve, and the right ventricle is hypoplastic. This form is associated with the presence of ventriculo-coronary arterial fistulas in 30% of cases.

• 2.

  PA type II (25% of cases): the tricuspid valve is incompetent or insufficient and there is a normal or, more frequently, a dilated right ventricle. This form of PA can be associated with anomalies of the tricuspid valve (e.g., Ebstein anomaly or tricuspid dysplasia; see Chapter 80 ).

Manifestations of Disease