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J Thorac Cardiovasc Surg 1997;114:871
© 1997 Mosby, Inc.

LETTERS TO THE EDITOR

The structure of the aortic root

Department of Anatomy and Embryology^a
Leiden University
P.O. Box 9602
2300 RC Leiden, The Netherlands

Reply to the Editor:

We thank Professor Anderson for his interest in our recent article. ¹ First of all, we must apologize for having missed the article by Sutton, Ho, and Anderson ² in our literature survey, and consequently for not having discussed it, while preparing our article. Should the wrong impression have been evoked that we deliberately omitted the article, we can assert that this is not our style.

The article by Sutton, Ho, and Anderson ² is certainly interesting and deservedly emphasizes the role and build of the interleaflet triangles. Indeed, these authors deserve credit for mentioning "a very thin layer of elastic tissue on the luminal surface" of the interleaflet triangles. What surprised us most, however, during our investigations is that this elastic tissue appears to be isolated from the other areas of elastic tissue. Although we have to consider that a more refined technique may show the elastic tissue to be continuous, we do think it is interesting from a developmental point of view. Likewise, as Professor Anderson suggests, the conus tendon is intriguing and has our attention in our morphogenetic studies.

With respect to the subpulmonary infundibulum, we are well aware that the subpulmonary infundibulum is not made of the ventricular septum proper. We (M.M.B. and A.C.G-de G.) have investigated this issue extensively and also clarified its morphogenesis. ^3-6 We are somewhat surprised by Professor Anderson's comment, as he was the one who invited us, some years ago, to write a review on the morphologic and embryologic correlations of the outflow tract. ³ The most important message from the latter article was that because of the asymmetric configuration of the level of the arterial orifices, already present in early embryonic hearts, the separation process results in the formation of the posterior wall of the pulmonary infundibulum, "rather than a septum between both outflow tracts." Figs. 1, 3, and 4 of that article emphasize that this (muscular) part of the pulmonary infundibulum is adjoining the ascending aorta, from which it is separated "by loose fibrous tissue and can thus not be called an `actual' outlet septum." In the discussion of that article, we stated that our findings were in agreement with the observations of Anderson, Becker, and Tynan, ⁷ who said that "it is not a septal structure at all." It appears that modesty with "self-quotation" does not always pay. In our recent paper ^1c on the pulmonary and aortic roots, we did not repeat this discussion because we assume that surgeons performing the Ross procedure do know these morphologic details. When mentioning that part of the pulmonary anulus inserts into "the septal part of the right ventricular myocardium," we used this designation to distinguish its location which, strictly speaking, is the myocardium immediately above the ventricular septum proper. To avoid misunderstanding, we will consider a more strict formulation in the future.

There remains, however, one issue to be discussed. We do not agree with Professor Anderson's statement that the autograft in a Ross procedure "does not possess a septal component." Most of the autograft is taken out of the freestanding myocardium in a plane approximately perpendicular to the subpulmonary myocardial surface. The most critical part of dissecting the autograft, however, concerns the portion that is scooped out in a plane between slightly oblique and parallel to the surface on the right ventricular side of the curved anterior part of the ventricular septum, thereby avoiding the septal branch of the left coronary artery. Should the section be made perpendicular to this part of the septum, the chances of damaging the coronary branch would be increased and the lumen of the left ventricle anterior to the subaortic area would be opened. Thus this part of the myocardium is not "freestanding" but an "actual" part of the ventricular septum. Unfortunately, the illustration accompanying Professor Anderson's letter does not provide a proper view of this area. Morphogenetically, we consider this part of the septum to be the most cranial part of the primary septum formed by the primary fold.

12/8/84948

References

1. Hokken RB, Bartelings MM, Bogers AJJC, Gittenberger-de Groot AC. Morphology of the pulmonary and aortic roots with regard to the pulmonary autograft procedure. J Thorac Cardiovasc Surg 1997;113:453-61.
   
2. Sutton JP III, Ho SY, Anderson RH. The forgotten interleaflet triangles: a review of the surgical anatomy of the aortic valve. Ann Thorac Surg 1995;95:419-27.
   
3. Bartelings MM, Gittenberger-de Groot AC. The outflow tract of the heart: embryologic and morphologic correlations. Int J Cardiol 1989;22:289-300.
   
4. Bartelings MM, Gittenberger-de Groot AC. Morphogenetic considerations on congenital malformations of the outflow tract. Part 1. Common arterial trunk and tetralogy of Fallot. Int J Cardiol 1991;32:213-30.
   
5. Bartelings MM, Gittenberger-de Groot AC. Morphogenetic considerations on congenital malformations of the outflow tract. Part 2. Complete transposition of the great arteries and double outlet right ventricle. Int J Cardiol 1991;33:5-26.
   
6. Bartelings MM, Gittenberger-de Groot AC. The arterial orifice level in the early human embryo. Anat Embryol 1988;177:537-42.
   
7. Anderson RH, Becker AE, Tynan M. Description of ventricular septal defects—or how long is a piece of string? Int J Cardiol 1986;13:267-78.
   

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