Introduction
This is an unusual condition (accounting for 5 per cent of all cases of pulmonary atresia (PA), although commoner in Eastern Asia) but one with a broad spectrum of treatment options depending on the degree of development of the right ventricle (RV). The commoner varieties of PA (i.e. PA with ventricular septal defect (VSD), tetralogy of Fallot with PA, PA with major aorto-pulmonary collateral arteries (MAPCAs)) are associated with the presence of a large VSD, which provides an outlet for the RV. However, occasionally, PA can occur in the absence of any VSD – in which case there is no outlet for the RV. This is known as ‘pulmonary atresia with intact ventricular septum’ (PAIVS). With no exit from the ventricular chamber, the pressure within the RV can be very high.
The consequence of this is twofold:
1. A lack of forward flow through the right ventricle can lead to varying degrees of underdevelopment or hypoplasia of the RV. This is thought to correlate with the point in fetal development at which the PA develops – the later it occurs, the better is the development of the RV.
2. The pressure within the cavity of the ‘cul-de-sac’ of the RV can become very high, leading to myocardial hypertrophy, endocardial damage and the creation of fistulous communications between the (high-pressure) RV cavity and the coronary arterial circulation. If these fistulae become well developed, then flow into the coronary circulation becomes retrograde from the right ventricular cavity into (usually) the right coronary system. In severe cases, the consequence is that the coronary circulation becomes dependent on this retrograde flow driven by high right ventricular pressure (so-called right ventricular-dependent coronary circulation), and the fistulous flow creates a dilated right coronary system. This creates a fragile coronary circulation at risk of coronary steal, typically in situations of low aortic diastolic pressure (Figure 13.1).
The key to management and the ultimate destination in this condition is based on assessment of the RV size. The normal RV is described as being ‘tripartite’, consisting of an inlet portion, an outlet portion and an apical trabecular portion. Assessing the volume of the right ventricular cavity in a neonate can be very difficult in view of its multiple thick trabeculations and its asymmetrical shape, and echocardiographic assessment of right ventricular volume is notoriously unreliable. Thus, the tricuspid valve dimension is usually used as a surrogate marker of right ventricular size and based on the Z-score of the predicted size according to body surface area (BSA). Table 13.1 summarizes the predictive outcome for the RV in the setting of PAIVS based on tricuspid valve size. RVs that are ‘bipartite’ (i.e. no apical trabecular portion) are very rarely likely to be suitable for biventricular repair.
| Z-score of tricuspid valve | Composition of RV | Likely destination |
|---|---|---|
| Larger than −2 | Tripartite | Biventricular repair |
| −2 to −5 | Tripartite ± bipartite | 1½-Type repair |
| Smaller than −5 | Bipartite | Univentricular repair (Fontan pathway) |
Diagnosis and Presentation
Patients present as newborns with cyanosis, and survival is duct dependent. Patients with a patent ductus may remain stable but will have varying degree of cyanosis, but if presentation is at the time of duct closure, then the baby may present with circulatory collapse and need resuscitation and ventilation. All patients need prostaglandin E2 infusion.
The mainstay of diagnosis is with echocardiography, and other imaging modalities are not usually required. MRI or CT may be indicated if there is concern about the branch pulmonary artery anatomy or size. Echo will confirm the diagnosis and also define the structure and size of the RV (atrial septum above, with particular focus on tricuspid valve (TV) size) as well as the presence of any coronary fistulae.
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