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Ann Thorac Surg 2004;77:1881-1882
© 2004 The Society of Thoracic Surgeons
a Cardiac Unit, Institute of Child Health, University College, London, United Kingdom
* Address reprint requests to Dr Anderson, Cardiac Unit, Institute of Child Health, 30 Guilford St, London WN1N 1EH, UK
e-mail: r.anderson{at}ich.ucl.ac.uk
The investigation by Hosseinpour and colleagues [1] provides important additional information concerning the location of the atrioventricular conduction tissues in patients with congenitally corrected transposition. In this setting, in most instances, the atrioventricular conduction axis takes its origin from an anomalously located atrioventricular node, rather than the regular atrioventricular node found at the apex of the triangle of Koch [2]. But this is not always the case, and, until now, no logical explanation has been given to explain why, in some cases, the atrioventricular bundle arises from a regularly positioned atrioventricular node.
Congenitally corrected transposition, of course, is the combination of discordant connections of the cardiac segments at both the atrioventricular and ventriculoarterial junctions. As such, it can exist either in the usual arrangement, or in a mirror-imaged variant. To date, as explained by Hosseinpour et al [1], in all the cases examined histologically, all those with the mirror-imaged variant ("situs inversus") have had the atrioventricular conduction axis arising posteriorly from a regularly positioned node, rather than being displaced anterosuperiorly as in the usual situation. And, as also explained by Hosseinpour et al [1], in a small minority of the cases with usual atrial arrangement ("situs solitus"), the conduction axis has been found in posterior rather than anterior location. The accepted explanation thus far for these apparently contradictory findings has been that, in the cases with minor-imaged arrangement, the ventricular mass is arranged in usual fashion, with d-looping, or right-hand ventricular topology. Because of this, it was argued, the atrioventricular node would be normally positioned [3]. There is, however, a deficiency in this logic. As already indicated, the conduction axis can still be located posteroinferiorly even with left-hand ventricular topology ("l-looping"). Furthermore, if the abnormal position of the conduction tissues in those with usual arrangement depended exclusively on the presence of left-hand ventricular topology, or "l-looping," then the conduction tissues would also be expected to be abnormal when the normally structured heart was seen in the setting of mirror imagery with concordant segmental connections. In reality, the conduction tissues are themselves mirror-imaged in this setting, but are otherwise normally located. Hosseinpour and colleagues [1] have now proposed and tested a much better explanation for the arrangement as seen with the mirror-imaged variant, an explanation that also holds good for identifying those rare instances in which patients with discordant atrioventricular connections in the usual setting can still possess a "regular" atrioventricular node that gives rise to a penetrating atrioventricular bundle. Furthermore, their account explains also the existence of those cases in which the posterior bundle coexists with an anterior node also giving rise to a penetrating bundle, the two bundles then combining to form a "Monckeberg" sling [2].
Their explanation is based on the concept of septal malalignment, as proposed in our own initial studies [2, 4]. In our earlier studies, however, we had been at a loss to explain why the septums were apparently better aligned in the cases with mirror-imaged atrial arrangement. Hosseinpour and colleagues [1] have now elegantly solved the conundrum. They have observed that, in all of the described examples of congenitally corrected transposition with mirror imagery in which the conduction tissues have previously been studied, there was either pulmonary atresia or severe pulmonary stenosis. They rightly indicate that the absence of a patent outflow from the morphologically left ventricle serves also to remove the "malalignment gap" that usually interposes between the atrioventricular node and the regular atrioventricular bundle at the apex of the triangle of Koch.
Parts of their account, however, still leave room for improvement. They comment that congenitally corrected transposition is "also known as l-TGA." This may well be true in the majority of cases, but certainly not in all. We know that the aorta is "d-transposed" in almost all the cases found with mirror-imaged atrial arrangement. Those who continue to use "l-TGA" as a synonym for corrected transposition are taking the segmental notation of Van Praagh [5] out of context. The correct way of describing those cases of congenitally corrected transposition with usual atrial arrangement and left-sided aorta is as "transposition {S, L, L}," while those rare cases of "regular" transposition with concordant atrioventricular connections and left-sided anterior aorta are properly designated as "transposition {S, D, L}." Codification of the full segmental arrangement is essential to show the full picture.
In their description of the background to the discovery of the anterior node, the authors then do less than justice to Monckeberg [6] and Lev and colleagues [7]. According to Hosseinpour and colleagues [1], "in the index case of Monckeberg, cited by Bharati and Lev, cc TGA was associated with double outlet right ventricle." There are two problems with this assertion. In the first place, if there is double outlet right ventricle, then the heart should no longer be described as displaying "transposition." Double outlet right ventricle can certainly be found in association with discordant atrioventricular connections, and Monckeberg certainly described the conduction tissues in such a case [6]. It is less than perfect, however, to describe double outlet right ventricle in this setting as representing "congenitally corrected transposition." "Transposition" is best considered synonymous with discordant ventriculoarterial connections, or alignments. Discordant ventriculoarterial connections cannot coexist with double outlet. Description of these categories should represent an "either-or" situation. The aorta can certainly be anterior in the setting of double outlet right ventricle, but is best not described using the term "transposition."
It is the credit due to Monckeberg that is perhaps more important. The significance of Monckeberg's case had been recognized long before the paper published by Bharati and Lev in 1978 [8]. Lev, with other colleagues, had discussed the significance of his findings in 1958, a report of the conduction tissues in hearts with common atrioventricular orifice [6]. Monckeberg's observations, nonetheless, remained neglected by the surgical community even after Lev's discussions, as had other important studies published in the German literature [9]. The surgical significance of the anterior node became evident in the early 1970s [2, 4]. At that time, I had just returned from a year spent in Amsterdam. During my studies, my mentor, Dirk Durrer, had commented "the Anglo-Saxons spend all their time rediscovering the old German literature." When considering knowledge of the location of the conduction axis in hearts with discordant atrioventricular connections [6, 9], it was difficult to quarrel with this assertion. We should not, therefore, devalue these original contributions in the German literature. But at least now, thanks to the study of Hosseinpour and colleagues [1], we have a rational explanation as to why the patients studied thus far with congenitally corrected transposition in the mirror-imaged variant had their bundles of His arising from "regular" atrioventricular nodes.
References
This article has been cited by other articles:
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  M. Ly, E. Belli, B. Leobon, C. Kortas, O. E. Grollmuss, D. Piot, C. Planche, and A. Serraf Results of the double switch operation for congenitally corrected transposition of the great arteries Eur. J. Cardiothorac. Surg., May 1, 2009; 35(5): 879 - 884. [Abstract] [Full Text] [PDF]
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 T. Shin'oka, H. Kurosawa, Y. Imai, M. Aoki, M. Ishiyama, T. Sakamoto, S. Miyamoto, K. Hobo, and Y. Ichihara Outcomes of definitive surgical repair for congenitally corrected transposition of the great arteries or double outlet right ventricle with discordant atrioventricular connections: Risk analyses in 189 patients J. Thorac. Cardiovasc. Surg., May 1, 2007; 133(5): 1318 - 1328. [Abstract] [Full Text] [PDF]
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