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Ann Thorac Surg 1995;59:562-564
© 1995 The Society of Thoracic Surgeons
Department of Paediatrics, National Heart & Lung Institute, London, United Kingdom
As the French say, ``chacun à son goût.'' Nomenclature is, perhaps, very much a matter of taste, especially when the taste is based on a particular tradition. Before the introduction of the segmental approach, lesions tended to be pigeon-holed into well-recognized categories according to their characteristic morphology. Complex and unusual malformations were usually consigned to the ``miscellaneous'' group. The advent of segmental diagnosis changed that, with each case being treated strictly upon its own merits. The problem that I find with the concept of segmental notation, however, is its cryptic nature when applied to rare and unusual lesions. Thus, does the patient described in the report by Santini and associates [1] in this issue of The Annals really have the typical morphology of tetralogy of Fallot? And does the chosen title convey the morphology present to the working surgeon?
Most surgeons would recognize immediately typical tetralogy of Fallot as seen in the operating room when opening the right ventricle (or approaching through the tricuspid valve). The aortic orifice would be overriding the crest of the ventricular septum, this made possible by the presence of a large interventricular communication. The right ventricular component of the subaortic outlet would be separated from the narrowed anteriorly located subpulmonary infundibulum by the malaligned outlet (infundibular) septum (Fig 1A
). These characteristics depend not only on the interrelations of the infundibular components themselves, but also on their relationships to the rest of the right ventricle. In this regard, tetralogy of Fallot almost always exists in hearts with usual atrial arrangement (situs solitus), with concordant atrioventricular connections, and with connections between the ventricular mass and great arteries that can vary between being concordant or double-outlet connection from the right ventricle. This difference, of course, depends upon the precise attachments of the overriding aortic valve. In the majority of cases, the aortic valvar leaflets are connected mostly in the left ventricle so that the ventriculoarterial connections are concordant. Because the arterial trunks are normally related, in segmental notation this overall arrangement for the heart is described as {S,D,S}. Tetralogy of Fallot also can be found rarely when the entire heart, along with the remaining organs of the body, are arranged in mirror-image fashion (Fig 1B). The segmental notation for this variant is {I,L,I}.
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What, then, is tetralogy of Fallot {S,D,I}? This notation indicates that the atrial chambers occupy their anticipated location (S = solitus) and are connected to appropriate ventricles that exhibit right-hand topology (D-loop). The arterial segment of the heart, however, is mirror-imaged (I = the pulmonary trunk located anteriorly and to the right of the aorta with the bifurcation swinging rightward and posteriorly around an aortic arch that swings initially leftward but then descends over the right bronchus). But how can such an arterial segment take its origin from ventricles with right hand topology (D-loop)? This depends entirely on one's definition of the arterial segment. My own preference is to define the arterial segment as starting at the ventriculoarterial junction. Within my definition, the ventricular outlet components are considered as part of the ventricular mass. Within the segmental approach as promoted by the Boston group [1], the infundibular structures are taken to belong to distal cardiac segment, which is then described as ``infundibuloarterial''. It is this definition that permits tetralogy of Fallot to be described in the {S,D,I} variant. Thus, the pulmonary trunk arises anteriorly and rightward from the right ventricular outlet above a restrictive completely muscular subpulmonary infundibulum. This infundibulum is separated by the malaligned outlet septum from the posterior and leftward subaortic outlet, which overrides the crest of the ventricular septum but is connected predominantly to the left ventricle. The subaortic ventricular septal defect (Fig 2A) is cradled between the limbs of the septomarginal trabeculation (septal band). Although it is difficult to be sure, I presume that the defect in the described case had a muscular inferior rim separating the ventricular septal crest from the membranous septum, which is described as intact.
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). To my eyes, this infundibular morphology in relation to the right ventricle is much more comparable with the arrangement seen in hearts with concordant atrioventricular and discordant ventriculoarterial connections (complete transposition) with the pulmonary trunk overriding an anterior muscular malalignment defect (see Fig 2A). All that would be required to have such a case transformed into the variant described by the Boston group would be to have the aorta ``plugged in'' to the overriding outlet usually supporting the pulmonary trunk, and the pulmonary trunk, instead of the aorta, connected to the narrowed right-sided and anterior muscular infundibulum. This, of course, is morphogenetic speculation on my part [2], but no more speculative than the concept propounded by the Boston group [1], which depends upon the ventricular outlets developing in concert with the arterial trunks rather than with the ventricular trabecular components. Indeed, in terms of speculative morphogenesis, it is an easy matter to imagine the lesion described by the Boston group as being part of a spectrum of lesions belonging to the group of hearts with double-outlet right ventricle, left-sided aorta, and subaortic ventricular septal defect. The change from such a heart with double-outlet from the right ventricle to the described lesion with concordant ventriculoarterial connections simply requires the aorta to ride the septal defect so as to take its origin predominantly from the left ventricle. But this interpretation would require double-outlet right ventricle to be recognized as a ventriculoarterial connection in the presence of fibrous continuity between an arterial and an atrioventricular valve. I am not sure whether the Boston group acknowledges this possibility, as my understanding is that they prefer to diagnose double outlet on the basis of infundibular morphology rather than according to the connection of the arterial trunks with their supporting ventricles. Be that as it may, had the aortic and mitral valves in the case described by the Boston group been separated by just 1 mm of infundibular musculature, the case would no longer have been categorized by them as tetralogy of Fallot. Instead, if my understanding of their system is correct, it would have been called anatomically corrected malposition {S,D,L}. Then, still with this millimeter of infundibular musculature separating the aortic and mitral valves, if the aorta had arisen predominantly from the right ventricle, the case would indeed have been called double-outlet right ventricle {S,D,L}. So, perhaps our difference in tastes reflects 1 mm of infundibular musculature. But my taste is also to seek for clarity when naming malformed hearts. I do not believe that ``tetralogy of Fallot {S,D,I}'' describes clearly this very rare entity. I would be surprised if this title provided many surgeons with a practical account of the lesion described. It may also be that not many surgeons are enlightened concerning the anatomy having read this editorial. This reflects the true complexity of this lesion, which I have yet to encounter myself in either the clinical setting or as an autopsied specimen. Here we return to tastes and approaches. In describing rarities, I believe that a precise, even lengthy, account is much more important than a brief title. My preference, therefore, would be to describe a heart of this kind as having usual atrial arrangement, concordant atrioventricular and ventriculoarterial connections, but with the left-sided orifice of the aorta, with fibrous continuity between its valve and the mitral valve, overriding a muscular outlet ventricular septal defect, the pulmonary trunk arising from a stenotic rightward and anteriorly located complete muscular infundibulum. I would complete my account with a description of the anomalous course of the right coronary artery, the location of the aortic arch, and the other associated malformations, because all these features are important.
Footnotes
Address reprint requests to Dr Anderson, Department of Paediatrics, National Heart & Lung Institute, Dovehouse St, London, SW36LY, United Kingdom.
References
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  R. H. Anderson How Should We Optimally Describe Complex Congenitally Malformed Hearts? Ann. Thorac. Surg., September 1, 1996; 62(3): 710 - 716. [Abstract] [Full Text]
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R. Van Praagh Tetralogy of Fallot {S,D,I}: A Recently Discovered Malformation and its Surgical Management Ann. Thorac. Surg., November 1, 1995; 60(5): 1163 - 1165. [Full Text]
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