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 ).
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.
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.
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.
Genetics and Epidemiology
PA + VSD comprises approximately 1% to 2% of all congenital heart defects, or 7/100,000 live births. Approximately 10% to 20% of individuals with tetralogy of Fallot have the PA + VSD variant. Importantly, 22q11 deletions are more commonly found in patients with PA + VSD (40%) than tetralogy. Those with the deletion typically have a more complex pattern, with small pulmonary arteries and MAPCA dependence.
Early Presentation
Patients with PA + VSD present with varying severity of cyanosis, determined by the extent of pulmonary vasculature and presence of MAPCAs. These maintain pulmonary blood flow when the ductus arteriosus closes (often later than usual). If MAPCAs are insufficient, a child will be given prostaglandins until a surgical shunt is created to provide adequate pulmonary blood flow. If MAPCAs are too abundant or unrestricted (less common), pulmonary blood flow increases as the pulmonary vascular resistance falls, and pulmonary congestion with heart failure symptoms will result. Without surgery to either increase or limit pulmonary blood flow, prolonged survival is unlikely. Those with adequate but not excessive pulmonary blood flow can survive into adulthood without surgery, although this well-balanced circulation occurs infrequently.
Management
The early management goals are to ensure adequate pulmonary blood flow without overcirculation, specifically to (1) establish a confluent, functional pulmonary vasculature, (2) achieve an RV-PA connection, and (3) close the VSD with a patch. The means of achieving this have evolved over the past several decades. In many older adult survivors this likely involved a multistage approach with several operations in childhood ( Fig. 48.4 ). Surgeons are now more frequently able to meet these goals with a single surgery. In children, central pulmonary artery size and the ability to achieve a repair predict overall survival; long-term outcome is good in patients in whom a repair is achieved.
Many adults will have undergone a palliative systemic to pulmonary arterial shunt procedure early in life to improve pulmonary blood flow. Several shunt varieties have been used over the years and are well described elsewhere. A Blalock-Taussig (BT) shunt, first performed in 1944, marked the beginning of the era of surgical intervention in cyanotic congenital heart disease. The shunt connected the subclavian artery with the ipsilateral pulmonary artery. It was usually placed on the side opposite the Ao to avoid kinking. The modified BT shunt uses a Gore-Tex conduit between the subclavian and pulmonary artery to maintain pulsatile flow to the arm and better control the shunt volume (see Fig. 48.4B ) and is now the most common systemic to pulmonary arterial shunt.
Other options include a Waterston-Cooley shunt (between the ascending aorta and the RPA), Potts shunt (between the descending aorta and LPA), or central shunt (interposition graft from ascending aorta to the MPA). These are rarely used by surgeons in the current era because complications such as severe distortion of the pulmonary arteries or pulmonary arterial hypertension are more common than with the BT shunt. However, they all may be seen in surviving adults. A Melbourne shunt, more recently introduced, uses an end-to-side anastomosis of the ascending aorta to the pulmonary artery.
For patients with severely atretic pulmonary arteries, unifocalization is required to reconstruct the pulmonary vascular bed from available vascular tissue, including MAPCAs. Unifocalization involves painstaking dissection and reunion of vessel walls, with synthetic material placed to bring the RPA and LPA in communication. This process is often staged through several surgeries (see Fig. 48.4 ). When successful, unifocalization allows for placement of a valved RV-PA conduit and VSD closure. Treatment with a single-staged surgical procedure is becoming more common and/or a hybrid catheter/surgical-based approach. An objective assessment of the adequacy of arborization can guide decision making early on. Two schemes for quantifying pulmonary vasculature are the McGoon ratio and the Nakata index. Decisions are sometimes based on intraoperative assessment of pulmonary blood flow. In patients with hypoplastic pulmonary arteries treated with an initial palliative strategy, there was no difference in the degree of increase of the Nakata index at 1 year in those who received a systemic to pulmonary artery shunt and those in whom an RV-PA connection was established, although the rate of severe postoperative complications was higher in the systemic shunt group.
Single ventricle palliation may be necessary if the RV is not sufficient to sustain independent pulmonary circulation. However, creation of a Fontan pathway may not be an option if the pulmonary vasculature is not favorable.
Long-Term Outcome
Adult providers are obligated to understand the early interventions made on an individual patient. The provider must review the past records to understand details of the patient’s original anatomy and subsequent interventions ( Table 48.1 ). Complications are the rule rather than the exception in PA + VSD, and all patients deserve regular, informed follow-up.
| Repaired Patients |
| RV-PA conduit stenosis and regurgitation—due to calcification and degeneration of the conduit over time RV pressure overload—due to conduit stenosis, branch pulmonary artery stenosis, stenoses in unifocalized MAPCAs or hypoplastic pulmonary arteries, or arborization defects of pulmonary vasculature Right heart failure—due to RV pressure or volume overload Tricuspid regurgitation—due to right heart failure Left heart failure—due to long-standing volume overload (excess circulation from MAPCAs or aortic insufficiency), or coexistent RV failure Aortic root dilatation and regurgitation—may be progressive Endocarditis—in conduit or on other residual lesions Arrhythmias—supraventricular (atrial fibrillation, atrial flutter, or atrial tachycardia), usually related to right heart failure. Ventricular arrhythmias may be related to ventriculotomy, intrinsic myocardial abnormalities, or progressive ventricular dilatation and dysfunction |
| Palliated and Unoperated Patients |
| Cyanosis—due to inadequate pulmonary blood flow Pulmonary hypertension—(may be segmental) due to chronically excessive blood flow in lung segments supplied by large, unrestrictive MAPCAs or shunts. Left ventricular dysfunction—due to long-standing volume overload from MAPCAs, myocardial ischemia from cyanosis, or RV failure Aortic root dilatation and regurgitation—may be progressive Arrhythmias—as previous Stroke—due to paradoxical emboli from intracardiac communications or in situ thrombosis related to erythropoiesis |
Adult unoperated patients are uncommon. They likely have either unprotected pulmonary blood flow and Eisenmenger physiology or limited pulmonary blood flow from resistance in MAPCAs. Intervention on such a patient is rarely justified but is determined based on thorough review of clinical status, existing pulmonary blood flow, and biventricular function.
Palliated patients will have undergone a shunt or unifocalization, but further surgery to close the VSD and establish RV-PA connection may not have been possible. These patients remain cyanotic. If stable and with few or no symptoms, long-term survival is reasonable, and further complex, risky surgical procedures may not be warranted. In rare circumstances, palliated or unrepaired patients without RPA-LPA confluence may have different hemodynamics in the two lungs, such as low PVR in one and high PVR in the other.
The vast majority of adults will have undergone VSD closure and RV-PA conduit placement but are not free from complications or further intervention. Conduit stenosis ( Fig. 48.5 ) is common, and many adults will have had one or two surgical conduit replacements already. Stenosis may be present at areas of conduit anastomosis with major branch pulmonary arteries. Although conduit longevity is generally better in adults than in children, reoperations for conduit stenosis, regurgitation, or endocarditis are not uncommon in adults. Factors associated with shorter conduit longevity include age, smaller conduit size, non-Dacron conduit material, and higher pulmonary arterial pressure, but most data come from pediatric populations, and predictive factors in adults are not well defined. Approximately one-half of patients will have required reoperation within 10 years of initial repair, and two-thirds of patients at 20 years.
