The significance of systemic-to-pulmonary collateral arteries

In their brief report [1], Zhou et al. describe an individual with tetralogy of Fallot and pulmonary atresia, in whom the pulmonary arterial supply was via a tubular aortopulmonary window. The pulmonary arterial supply, however, was supplemented by multiple systemic-to-pulmonary collateral arteries. Their case is unusual on several counts. In the first instance, as shown by their excellent images, the importance of which they rightly emphasize, the pulmonary trunk was of good size, as were the right and left pulmonary arteries. In the second instance, the aortopulmonary window was an extensive tubular entity. The channel was rightly described, nonetheless, as being an aortopulmonary window since it was intrapericardial. In their patient, it might more appropriately have been described as an aortopulmonary tunnel. The third unusual finding was the presence of 4 systemic-to-pulmonary collateral arteries. These vessels are more usually found when the intrapericardial pulmonary arteries themselves are grossly hypoplastic. The conundrum then, both in diagnosis and in determining the optimal surgical approach to repair, is to determine the proportions of the pulmonary parenchyma supplied by the intrapericardial pulmonary arteries as opposed to the systemic-to-pulmonary collateral arteries. In the patient described, this was not such a problem, since the intrapericardial arteries were themselves of significant size, and presumably supplied the entirety of the pulmonary parenchyma. Despite this fact, the surgeons opted to anastomose the collateral arteries to the pulmonary trunk, choosing to ligate only one of the 4 collateral arteries, along with the tubular aortopulmonary communication. It is difficult to fault their choice in the light of the excellent outcome.

Their findings are significant relative to the more general considerations of the anatomical findings in the setting of tetralogy with pulmonary atresia. In this regard, the authors are correct when describing their patient as having tetralogy with pulmonary atresia. The intracardiac anatomy was, indeed, that of tetralogy of Fallot, but with pulmonary atresia rather than pulmonary stenosis. Many authors continue to describe this constellation of abnormal anatomical findings as ‘pulmonary atresia with ventricular septal defect’. This description is not in itself incorrect. The anatomy seen in the reported patient, however, is but one of the variants that can justifiably be grouped together as representing pulmonary atresia in the setting of deficient ventricular septation. It is only in the subset of patients having the phenotypic features of tetralogy of Fallot that it is frequent to find the pulmonary arterial supply provided by systemic-to-pulmonary collateral arteries. Not all individuals with this anatomy, of course, have systemic-to-pulmonary collateral arteries. In around half, the pulmonary arterial supply is through the arterial duct. In this setting, the intrapericardial pulmonary arteries then usually supply all the pulmonary segments. Similar arrangements can more rarely be found when the pulmonary arteries are discontinuous, with each fed through an arterial duct. Or when, as in the current case, the confluent pulmonary arteries are fed through an aortopulmonary window. In the latter instance, nonetheless, it is exceedingly rare for the window to be as elongated and tubular as that shown in the patient of Zhou et al. [1].

Controversy continues to surround the issue of systemic-to-pulmonary collateral arteries on several counts. In the first place, it is better to describe them as being systemic-to-pulmonary, rather than aortopulmonary. This is because the collateral channels can arise from the brachiocephalic arteries, or from the coronary arteries. A second problem is that they are often distinguished from the intrapericardial arteries on the basis that the latter vessels are ‘native’. But the collateral arteries are just as native as those arising from the pulmonary trunk. The third question is whether the arteries are no more than enlarged bronchial arteries. The best way of resolving that dilemma would be to demonstrate the presence of true bronchial arteries in addition to the systemic-to-pulmonary arteries. The bronchial arteries are nutritive rather than oxygenating, and branch with the bronchial tree, but systemic-to-pulmonary arteries can satisfy both of these criteria. Since the vessels are unequivocally systemic-to-pulmonary channels, that remains the best descriptor. Once such collateral channels have been identified, the major persisting surgical dilemma is whether they should be unifocalized [2–5]. The answer to that conundrum will not be provided by anatomical studies. Suffice it to say that, on occasion, the systemic-to-pulmonary collateral arteries are the only source of pulmonary arterial supply. In this setting, there is a complete absence of the intrapericardial pulmonary arteries, and the vessel leaving the base of the heart can justifiably be considered to represent a solitary arterial trunk. In terms of clinical presentation, such individuals fall into the category of tetralogy with pulmonary atresia. And, in such a setting, unifocalization provides the only means of obtaining a biventricular circulation.

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