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J Thorac Cardiovasc Surg 1996;111:1106-1107
© 1996 Mosby, Inc.
LETTERS TO THE EDITOR |
Department of Pediatrics
National Heart and Lung Institute
London SW3 6LY, United Kingdom
To the Editor:
We read with great interest the report of Rubino and his colleagues
1 concerning various connections in hearts from patients with visceral heterotaxy and asplenia. We 2 have just reported a similar series of findings in hearts from patients with isomeric right atrial appendages, a group of patients that is very similar but not identical to those having visceral heterotaxy and asplenia. 3 Like Rubino and his associates, 1 we have also long been interested in this spectrum of malformations, and we were surprised that the Boston investigators chose to ignore all our previous work, 4-7 because some of our findings are surely pertinent to the topic of discussion. In fact, our latest study, comprising 124 cases, produces findings that are in close agreement with the study of Rubino and associates. 1
We disagree with the Boston group, however, on two areas of major surgical significance. The first concerns the matter of recognition of atrial arrangement (situs). Rubino and his colleagues 1 chose to ignore this matter in this publication, arguing that it had been the subject of two previous reports. 8,9 It is, perhaps, unfortunate that neither of those earlier accounts had been the subject of peer review in the generally accepted sense, and neither is published in journal format. Be that as it may, the subject of atrial arrangement is surely the key to the concept of visceral heterotaxy, the more so since one of the cited works of Rubino's group (their reference 10) 10 contends that isomerism of the atrial chambers is an erroneous concept. This, of course, depends entirely on the concept used to differentiate the atria. For many years, we have chosen to follow the excellent concept promulgated by Van Praagh and colleagues 11 for use in recognizing and differentiating components of the cardiac segments and dubbed by them the "morphologic method." In essence, this method suggests that features that are themselves variable should preferably not be used in differentiation. It seems to us that use of this criterion rules out the venous connections as a marker of atrial morphology since, as shown by both the Rubino study 1 and our own investigation, 2 they are remarkably variable in the setting of visceral heterotaxy. Yet, if we understand the previous publications 8,9 correctly, this is precisely the criterion they used to judge atrial "situs." Is this not a direct contravention of the morphologic method? If there were not a suitable alternative approach, such a departure would be acceptable. But an excellent alternative does exist. This is the structure of the atrial appendages based on the morphology of their junctions with the rest of the atrial segment. This emphasis on morphology is crucial, since we 2 agree with Rubino and associates 1 that neither size nor shape of the appendages is sufficiently constant to permit their recognition. Taking the extent of the pectinate muscles within the appendage relative to the vestibules of the atrioventricular junctions, in contrast, proved an absolute guide to distinction of morphologically right and left appendages not only in the normal heart, as illustrated by Van Praagh and Vlad, 12 but also in hearts from patients with visceral heterotaxy. 2 Use of this anatomic criterion enabled us in all cases studied 2 to recognize the presence of isomeric atrial appendages, not only morphologically right but also morphologically left. Venoatrial connections, however, were markedly variable, emphasizing that, in the strictest sense, it is the appendages that are isomeric and not the entire atrial chambers. This criterion of junctional morphology has also been shown to be valid in animal models of isomerism. 13,14
The concept of isomerism existing as a grouping within the spectrum of visceral heterotaxy then brings us to our second potential disagreement with the Boston investigators, again a feature of surgical impact. They described two cases having asplenia but in the presence of a coronary sinus. In none of our cases with isomeric right appendages (125 in all) did we encounter a coronary sinus defined on the basis of a circumflex venous channel running within the epicardial aspect of the atrioventricular junction. Indeed, the finding of anomalous coronary venous drainage is another key surgical feature in hearts with isomeric atrial appendages. 15 We wonder, therefore, if the patients in the Boston series with asplenia could have had either isomeric left appendages or, alternatively, one right and one left appendage, according to the nature of their junctions with the remainder of the atrial segment. We encountered two cases in our series with asplenia and visceral heterotaxy in which both the appendages were of morphologically left pattern.
There is then a third disagreement between our studies. Our findings showed that, according to anatomic criteria, the majority of cases in which the pulmonary veins connected to the atrial segment in hearts with asplenia and visceral heterotaxy could not be considered to represent normal connections. This is because the presence bilaterally of pectinate muscles extending around the atrioventricular junctions, together with the anomalous coronary venous drainage and the lack of atrial musculature at the insertions of the pulmonary veins, produces an arrangement quite dissimilar from the anticipated union of the pulmonary veins with the posterior wall of the morphologically left atrium. These differences have no relationship whatsoever with considerations of the site and formation of the primary and so-called secondary components of the atrial septum. At any event, as can be shown by dissecting any normal heart, the so-called secondary septum is no more than an infolding of the wall between the superior caval and pulmonary veins. The very absence of this structure, therefore, would indicate an abnormality in the arrangement of the pulmonary veins.
References
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