Pulmonary Atresia With Ventricular Septal Defect

General Overview

Pulmonary atresia (PA), or absence of a communication between the right ventricle (RV) and the main pulmonary artery (MPA), exists in two forms based on the presence or absence of a ventricular septal defect (VSD). Despite similar nomenclature, they are very disparate entities, each with a distinct management strategy and expected outcome. PA with a VSD (PA + VSD), discussed here, shares many structural and management features with tetralogy of Fallot. Patients usually have two functional ventricles and a VSD overriding the aortic valve (ie, “subaortic”). Pulmonary arterial development and hence pulmonary blood flow is variable but often facilitated by large collateral arteries stemming from the systemic arterial tree. In contrast, PA with an intact ventricular septum (PA + IVS) is characterized by a hypoplastic RV, a patent ductus arteriosus supplying blood to the lungs, and coronary fistulae. PA + IVS is discussed in Chapter 50 .

Like with many forms of congenital heart disease, PA + VSD manifests a wide spectrum of severity from simple to complex. In its simplest form the lesion is merely an extreme variant of tetralogy of Fallot with an imperforate pulmonary valve. Accordingly, the clinical management of tetralogy of Fallot (see Chapter 47 ) also largely applies to PA+VSD. In its more complex form, there is atresia of the MPA or major branches, wherein pulmonary blood flow is completely dependent on large collaterals. RV stroke volume exits through the overriding aortic valve, mixes with left ventricle (LV) output, and contributes to both the pulmonic and systemic circulations. This end of the spectrum is more similar to type 4 truncus arteriosus.

The major challenge in the management of PA + VSD is optimization of pulmonary blood volume and pressure, avoiding either too little or too much. Heterogeneity of pulmonary blood flow is the rule and complicates treatment considerably. The amount of native pulmonary vasculature present and the extent of collateral blood flow to the lungs determine the treatment approach for each individual. Collaterals, known as major aortopulmonary collateral arteries (MAPCAs), are often an essential element for the development of lung tissue and lung perfusion but can also present difficulties in the long term.

Anatomy

Pulmonary Vasculature

In simple cases in which atresia affects only the valve itself, the MPA may be present and reasonably sized. In more severe cases the pulmonary artery may be severely atretic or nonexistent, with the exception of a small fibrous band connected to the infundibulum. Absent flow through the pulmonary arteries in utero contributes to further atresia of the distal vessels, such that the lesion can essentially propagate its own severity. The extent of distal arborization may not be sufficient for blood to reach all portions of lung parenchyma. Lung segments not in communication with the branch pulmonary arteries are typically perfused via MAPCAs. Either lung may be smaller than usual as a result of inadequate perfusion.

Confluence between the right pulmonary artery (RPA) and left pulmonary artery (LPA) is another variable differentiating individuals along the spectrum of lesion severity. Branch PA confluence occurs in the majority (85%) and simplifies the initial management because all the intrapulmonary arteries are in communication and the pulmonary blood flow arises predominantly from a patent ductus arteriosus ( Fig. 48.1A ) or from MAPCAs, especially if the RPA and LPA are hypoplastic (see Fig. 48.1B ). When the RPA and LPA are not confluent, different parts of the lung are perfused strictly via MAPCAs (see Fig. 48.1C ).

Figure 48.1, Three patterns of pulmonary arterial anatomy in pulmonary atresia with ventricular septal defect. A, Well-formed central pulmonary arteries with normal arborization are present. Pulmonary blood supply is via a patent ductus. B , Central but hypoplastic pulmonary arteries are present and coexist with major aortopulmonary collateral arteries (MAPCAs). C, Central pulmonary arteries are absent and pulmonary blood supply is entirely via MAPCAs. D , Angiogram demonstrating the pattern in B : selective injection into a MAPCA retrogradely fills small pulmonary arteries that taper toward the atretic main pulmonary artery (MPA), producing a “seagull” sign. E , Angiogram demonstrating the pattern in C : an aortogram with injection into the descending aorta reveals large bilateral MAPCAs.

MAPCAs may be vessels of substantial diameter (>10 mm) with a muscular layer. They typically stem from the descending thoracic aorta ( Fig. 48.2 ) or any of its branches, including the subclavian, intercostal, bronchial, or celiac arteries. Rarely coronary arteries can also supply collaterals to the pulmonary circulation, usually without significant coronary steal. MAPCAs most often anastomose with the pulmonary artery branches proximally, and with somatic growth these anastomoses can become stenotic over time. These differ from acquired collateral blood vessels to the lungs associated with cyanosis, which usually join the pulmonary blood supply more distally at or near the precapillary level.

Figure 48.2, Maximum intensity projection reconstruction of a magnetic resonance imaging angiogram in a patient with pulmonary atresia with ventricular septal defect (VSD), shown in three different views. From the right, a large collateral MAPCA from the descending aorta is visible to the right pulmonary artery, which courses underneath the aortic arch and is confluent to the LPA, shown from the left. The center shows an anteroposterior (AP) projection, wherein the absence of a large main pulmonary artery (MPA) can be appreciated. Ao, Aorta; LPA, left pulmonary artery; MAPCA, major aortopulmonary collateral artery.

Intracardiac Anatomy

The VSD is typically a large, perimembranous, subaortic defect, as is seen in tetralogy of Fallot ( Fig. 48.3A and B ). Less commonly the defect may be subpulmonic, when the aorta is malposed anteriorly (such as a Taussig-Bing anomaly with transposition of the great arteries). The terminology may become inconsistent because there is only one semilunar valve. Hence the terms “double-outlet right ventricle” or “transposition of the great arteries,” although convenient, may be misnomers in the setting of coexistent pulmonary atresia.

Figure 48.3, Oblique coronal magnetic resonance imaging (A) and three-chamber view (B) showing a large ventricular septal defect with the aorta overriding both the right and left ventricles. Patient was not repaired, and hence there is persistent RV hypertrophy from systemic level pressures. Ao, Aorta; RV, right ventricle.

PA + VSD can also be associated with other congenital defects, including a right-sided aortic arch (25% of cases), dextrocardia, L-type malrotation, atrioventricular septal defects, or heterotaxy syndromes, especially when 22q11 deletion is present. Coronary anomalies are relatively frequently seen; a left anterior descending artery originating from the right coronary appears to be the most common. Management is more complex with these additional anatomic variants.

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