14.6.12 Pulmonary atresia

Pulmonary atresia with ventricular septal defect is an extreme form of Fallot in which there is no communication between the RV and PA. At birth, the patent ductus arteriosus is the only source of pulmonary blood flow. A third of children maintain flow to the PA with 2 to 6 major aortopulmonary collateral arteries (MAPCA) [5]. Children experience varying degrees of cyanosis depending on the degree of R-to-L shunting via the VSD and L-to-R shunting via the patent ductus arteriosus or collaterals. Long-term survival is rarely possible under these circumstances, since the PA is hypoplastic and the collaterals do not provide sufficient flow, while the connection between the aorta and the pulmonary arteries causes structural deterioration of these vessels leading to irreversible pulmonary arterial hypertension.

If collaterals are absent, this lesion constitutes a neonatal emergency, since closure of the ductus arteriosus results in death. Total correction is performed immediately if circumstances permit: patch over the VSD and RV-PA conduit (homograft or valved bovine jugular vein conduit). If this is not possible due to the specific circumstances of the case, a stent may be inserted percutaneously in the ductus arteriosus to prevent it from closing or a Blalock-type calibrated peripheral shunt may be constructed [5]. If MAPCA are present, the surgical strategy is based on unifocalisation, which involves transforming the system of collaterals into a single mediastinal vessel vascularising the PA trunk, and calibrating this to achieve PAP of approximately 30 mmHg. Preoperative catheterisation is required for optimal mapping of these vessels to differentiate competitive MAPCA (simple ligatures) from non-competitive or distal competitive MAPCA (compulsory unifocalisation) on which vascularisation of a lobe or pulmonary segment is dependent (Figure 14.61A). Survival at 10 years is 70-85% [1].

Anaesthetists face three key issues [6]:
 

Figure 14.61A: Diagram showing various types of surgical corrections in cases of MAPCA.

Pulmonary atresia with intact septum

Pulmonary atresia with intact ventricular septum is a complete fibromuscular blockage associated with varying degrees of RV and tricuspid valve hypoplasia. In 10-20% of cases, fistulas between the RV and epicardial coronary arteries render myocardial perfusion dependent on RV function, with RV pressure significantly raised due to the blockage impeding ejection [2]. Survival is ensured by an ASD (R-to-L shunt) and a patent ductus arteriosus kept open by a prostaglandin infusion. Closure of the patent ductus arteriosus immediately exacerbates cyanosis. Several therapeutic options are available depending on the degree of RV hypoplasia [5,6].
 

The RV is small, hypertrophic and under high pressure. If no coronary fistulas are present, it must be decompressed to allow its growth. Anaesthesia is subject to the same constraints as in cases of single ventricle defects (see Ventricular hypoplasia).

Special case: isolated pulmonary stenosis

While pulmonary stenosis is present in approximately 10% of congenital heart disease cases, it may also exist in isolation and may manifest itself late in adolescence as right ventricular hypertrophy followed by RV failure. The RV is often ischaemic as the O₂ requirement is raised while O₂ supply is compromised by intraventricular hypertension during systole. An increase in afterload occurring from birth causes concentric-type hypertrophy rather than RV dilation. Right heart function remains adequate as long as intraventricular pressure is < 50% of left heart pressure and there is no associated volume overload. Patients become symptomatic if RV pressure exceeds half of systemic pressure [7]. The valve is dome-shaped with a narrowed central opening (Figure 14.61B).
 

Figure 14.61B: Examples of congenital pulmonary stenosis – the valve is narrow, hypoplastic, and more or less cone-shaped [3]. 

 

Surgery is indicated if the maximum gradient is ≥ 60 mmHg and RV pressure > 0.7 times LV pressure [5]. Percutaneous valve repair by balloon dilation is the preferred treatment, but it is associated with major pulmonary insufficiency in 25% of cases. Although more invasive, surgical valvulotomy leads to excellent outcomes and 95% survival at 25 years.

Four key constraints apply to anaesthetic management of isolated pulmonary stenosis.
 

Once the PA is unclamped, the sudden increase in pulmonary flow may cause significant alveolar exudate. This pulmonary reperfusion lesion occurs in a quarter of all cases. High PEEP is beneficial [8].

 

 

 

© BETTEX D, BOEGLI Y, CHASSOT PG, June 2008, last update February 2020