Introduction
Sometimes referred to as ‘complex pulmonary atresia’, this rare group within the spectrum of pulmonary atresia (PA)/ventricular septal defect (VSD) is defined by the additional presence of major aorto-pulmonary collateral arteries (MAPCAs) that provide multiple sources of pulmonary blood flow arising from the thoracic aorta or its branches.
Table 12.1 summarizes categorization of pulmonary atresia. The first consideration is whether there is associated VSD or not (intact septum; see Chapter 13). When a VSD is present, then this is often considered as the extreme spectrum of tetralogy of Fallot – where the outflow obstruction is so severe that it has become atretic. This is reflected in the fact that the intra-cardiac anatomy is similar to that of tetralogy with a large sub-aortic peri-membranous VSD and overriding aorta. In the majority of PA/VSD, the branch pulmonary arteries are well developed with normal branching patterns and distribution within the lungs and are supplied by the ductus arteriosus. However, approximately 20 to 40 per cent of all cases of PA/VSD are associated with MAPCAs (typically two to six vessels that arise from the thoracic aorta or the brachiocephalic artery, most commonly around the level of the carina) supplying a variable degree of the lung parenchyma. The condition is characterized by its heterogeneity and the variable relationship between the MAPCAs and the native pulmonary artery system. The ductus may or may not be present, but if it is present, then it will supply some component of the native system rather than a MAPCA. DiGeorge syndrome is associated with 30 per cent of cases, usually at the more severe end of the spectrum with poor-quality pulmonary vasculature.
Table 12.1 Classification of Pulmonary Atresia
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Pulmonary blood supply can be categorized as follows:
1. Well-developed native pulmonary artery system supplying all areas of the lung. Variable MAPCAs feeding into the native system, but no areas of the lung supplied exclusively by MAPCAs.
2. Mixed distribution; under-development of native system to a variable degree with a combination of native vessels and MAPCAs supplying the lungs – some areas of the vasculature supplied exclusively by MAPCAs.
3. Complete absence of intra-pericardial pulmonary arteries. Lung supply is entirely through MAPCAs, which can be of variable size and quality.
In general, those in group 1 carry the best prognosis and those in group 3 carry the worst due to the fact that MAPCA distribution within the lung is often abnormal and underdeveloped, sometimes with tortuous and stenotic areas even within the lung tissue. However, there can still be variability even within these subgroups, and assessment of any case has to take into account the overall quality of the vasculature, which can be underdeveloped and patchy in any situation. Furthermore, the MAPCAs themselves typically run a tortuous and variable course from their origin into the lung, which can develop additional stenoses within them over time, even occluding in some cases.
Large MAPCAs can result in unprotected blood flow to areas of the lung with the risk of developing pulmonary vascular disease in these segments, whereas stenotic or small MAPCAs lead to under-perfusion and potential underdevelopment of the same. Consequently, the natural history and mode of presentation of these patients are equally heterogeneous – and reflect the underlying anatomy of the pulmonary blood flow.
Presentation and Investigation.
Most patients are cyanosed but relatively stable, enabling time for assessment and planning of treatment. The degree of cyanosis depends on the nature of the pulmonary blood flow, as described earlier, but severe cyanosis is unusual and is a bad prognostic sign, suggesting poorly developed vasculature. Cyanosed neonates may benefit from prostaglandin E2 if there is a ductus supplying part of the native system, but prostaglandin E2 will not have any effect on the MAPCAs themselves.
At the other end of the spectrum, patients with large MAPCAs may not be cyanosed due to such high pulmonary blood flow and are actually in congestive cardiac failure (CCF). More typically, patients lie between these two extremes and are moderately cyanosed – however, it is important to recognize that these patients are not ‘safe’ in that the apparently well-balanced circulation could include a mixture of some areas of the lung being over-perfused (and at risk of pulmonary vascular disease) and others under-perfused (and at risk of failing to develop).
Echocardiography is helpful to confirm the intra-cardiac anatomy and will usually identify the presence of MAPCAs arising from the aorta but cannot define the anatomy. Cardiac catheterization is essential in all cases to identify all MAPCAs and show their distribution within the lungs. Careful assessment of each injection will reveal the native system (if present) being supplied by the MAPCAs, which typically appear as a seagull-shaped image on the late phase of injection (see Figure 12.1B). MRI and CT angiography are essential adjuncts to catheterization to demonstrate the 3D relationship of the MAPCAs to the airways and the great vessels. Careful 3D reconstruction techniques are time consuming but extremely helpful for planning surgery, particularly in defining the relationship of MAPCAs to the main airways and the oesophagus (Figure 12.2).
