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Eur J Cardiothorac Surg 2005;28:855-856
© 2005 Elsevier Science NL

Editorial comment

The aortic valve: an everlasting mystery to surgeons

Cardiothoracic Surgery, University Hospital, Coimbra, Portugal

(Email: antunes.cct.huc{at}sapo.pt).

Despite its apparent simplicity, the anatomy, physiology and physiopathology of the aortic valve have persistently defied the comprehension of the surgeons. Literally, thousands of works have been published on these subjects and it does not cease to surprise us.

In this issue of the journal, Thubrikar et al. [1], from Charlotte, USA, describe an observational study on 14 patients with dilated aortic root and aortic regurgitation who were examined by transesophageal echocardiography. They measured the diameter of the annulus and of the sinotubular junction (STJ), the length of the free edge of the leaflets, and the height of the sinuses and of the leaflets, and compared these measurements with those obtained in silicone moulds of 19 normal human aortic valves. They found that the diameter of the annulus was equivalent and the sinotubular junction diameter was increased in dilated aortic roots, as compared to normal. Strikingly, the aortic sinuses appear to be higher and the leaflets larger than normal. Furthermore, the length of the free edge and the sinus height were all found to be increased in patients with dilated root. That is, their measurements "suggest that these anatomically normal leaflets were, however, not geometrically normal". Finally, they could not correlate the degree of regurgitation with any of the dimensions measured. They, therefore, conclude that "the dimensions of the leaflets may change together with aortic root dilatation" and recommend that "during valve sparing, it may be necessary to correct not only the dilatation of the aortic root, but also the length of the free edge of the leaflet in order to achieve a competent valve".

Coming from an author and group that have been notorious by their extensive work on the aortic valve and root, this is yet another very important study as, to my knowledge, nobody has reported these alterations before.

Naturally, some criticism may be levelled at the methodology used in the study, such as the relatively small number of patients studied, the use of TEE rather than intraoperative measurements, which the authors justified because of the preoperative planning of aortic valve reconstruction with a customized prosthesis, and the use of moulds of the normal valves, because these valves were usually not examined by TEE and consequently such recordings were not available. Nonetheless, these findings could justify earlier surgery for aortic regurgitation, prior to enlargement of the aortic valve leaflets in order to achieve aortic valve reconstruction, as questioned by the reviewers during the analysis for publication of this manuscript.

However new these findings may be, they cannot constitute a surprise. The lengthening of the free edge of the leaflet, which seems to parallel the increase in the distance between the commissures, and the increase in the height of the leaflets may point to an attempt to maintain cuspal coaptation and prevent or reduce regurgitation. It has been a common observation that aortic regurgitation occurs late during the process of STJ dilatation and may not begin until this has reached a critical value. On the other hand, as the authors have shown previously, in a landmark paper, both the annular and the STJ diameters change during the cardiac cycle, [2] which results from the elasticity of all the tissues that make up the aortic root, and this elasticity may obviously be altered in the pathological conditions that trigger aneurysm formation.

Based on the data presented, the authors have developed "tabulated guidelines to restore safe functional dimensions of the valve components, provided that the intraoperative measurements of the leaflet dimensions are accurate enough", which are the subject of publication in another journal [3]. But they are of the opinion that "it may not be necessary to recommend early surgery for AI, because the guidelines have been successful in correcting fairly advanced stages of AI. The rationale is that if a reliable way of fixing the valve is determined, AI can be let run its course as long as the patient can tolerate it".

On the other hand, none of the current methods of valve sparing during aortic root substitution contemplates the finding of increased length of the free edge of the cusps and incorporates routine shortening of these free edges. The techniques of remodelling and reimplantation developed by Yacoub et al. [4] and David et al. [5], as well as other techniques currently in practice are based on the assumption that many patients with aortic regurgitation seem to have anatomically normal leaflets and focus their attention onto the aortic sinuses and commissural insertion and, in fact, distinguish from each other by the emphasis placed on these aspects of the valve anatomy.

Unlike mitral valve repair, aortic valve conservation appears to be less reproducible, despite the fact that the aortic valve anatomy is seemingly simpler than that of the aortic valve, which raises many questions. The paper by Thubrikar et al. may bring some answers. Many failures of the procedure may be due to lack of knowledge of these data and this information provided by the authors could be very important in improving the results after this procedure.

Aortic regurgitation present in the dilated aortic root is mostly related to stretching of the free edges of the leaflets, preventing appropriate apposition (if the leaflets are structurally normal, showing the small Mercedes Benz-type star in the centre of the valvular orifice commonly seen both in echocardiografic imaging and during surgery). The enlarged leaflets indicate that just decreasing STJ diameter will not be sufficient to obtain a competent valve, because the leaflets have become too large for the valve orifice. Excessive surgical reduction of the size of the diameter of the sinotubular junction, and not of the ventriculo-aortic junction (annulus) may result in leaflet prolapse and valve incompetence. In these cases, it remains the option of free-edge shortening, using one of the several techniques that have been recommended for aortic regurgitation caused by isolated leaflet prolapse.

Current techniques of aortic valve sparing, most of which do not use scientific rules for selecting the graft diameter, thus need to be adapted in the light of this new knowledge. Nonetheless, coaptation of the leaflets may be different in different patients and may even not occur in some. Obviously, each patient is a different case and the surgical technique must be applied accordingly, but we must not ignore data such as that presented by the authors, even if that means to challenge time-honoured procedures.

	References

Top References

 

1. Thubrikar MJ, Labrosse MR, Zehr KJ, Robicsek F, Gong GG, Fowler BL. Aortic root dilatation may alter the dimensions of the valve leaflets. Eur J Cardiothorac Surg 2005;28:850-855.
2. Thubrikar M, Piepgrass WC, Shaner TW, Nolan SP. The design of the normal aortic valve. Am J Physiol 1981;241:H795-H801.
3. Labrosse MR, Beller CJ, Robicsek F, Thubrikar MJ. Geometric modeling of functional trileaflet aortic valves: development and clinical applications. J Biomech 2005(2005 Sept. 29; [Epub ahead of print]).
4. Yacoub M, Fagan A, Stassano P, Radley-Smith R. Result of valve conserving operations for aortic regurgitation [abstract]. Circulation 1983;68(Suppl):III321.
5. David TE, Feindel CM, Bos J. Repair of the aortic valve in patients with aortic insufficiency and aortic root aneurysm. J Thorac Cardiovasc Surg 1995;109:345-352.

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				R. H. Anderson The surgical anatomy of the aortic root MMCTS, February 19, 2007; 2007(0219): 2527. [Abstract] [Full Text] [PDF]

				R. H. Anderson Editorial comment: Demystifying the anatomic arrangement of the aortic valve Eur. J. Cardiothorac. Surg., June 1, 2006; 29(6): 1006 - 1007. [Full Text] [PDF]

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