Labyrinth in cardiac surgery: annuloplasty for aortic valvuloplasty

In contemporary cardiac surgery, aortic valvuloplasty is perhaps the only field that is still in its infancy. Surgeons are in a never-ending labyrinth of aortic valvuloplasty, and because of the uncertainty involved, performing aortic valve replacement on young patients with aortic regurgitation is a concerning situation. In Japan, aortic valvuloplasty was performed in only 8% of elective surgeries on patients with aortic regurgitation in 2014 [1] and that number remained almost unchanged in 2019 (preparing for submission). It has been estimated that a learning curve of 40–60 cases is required for aortic valvuloplasty [2]. Since facility consolidation is not achieved in Japan, aortic valvuloplasty has not become popular due to the low number of cases per facility.

What is the difference between aortic valvuloplasty and mitral valvuloplasty, which are so popular worldwide? The consensus seems to be that the advantages of the latter are that the valve leaflet tissue is abundant and thick, easy to manipulate, and only 2-dimensional alignment is required (as is the case with the bicuspid aortic valve). However, the distinct difference seems to be that the latter has the more popular, widely-used commercially available annuloplasty ring. For this reason, mitral valvuloplasty has been standardized as a straight forward and reproducible procedure, so it is now becoming a common surgery in the world, to the extent that it is performed even by robotic surgery.

Even in aortic valvuloplasty, a large annulus is identified as one of the greatest risk factors for failure, and the importance of annular support has been emphasized [3]. In the aortic valve reimplantation technique, the vascular graft itself fixes the annulus, but in the aortic root remodelling technique and isolated aortic valvuloplasty, it is desirable to add some kind of annular support, and various modifications have been proposed. The currently widely applied types are external suture annuloplasty [4], external flexible ring annuloplasty [5] and internal rigid ring annuloplasty reported by Jarral et al. [6] in this issue of EJCTS. This is followed by internal suture annuloplasty [7] and internal flexible ring annuloplasty [8] as a minority. Of these, only the external flexible ring and internal rigid ring are currently commercially available products. Partial annuloplasty is simple but less effective as annular support, and circular support is recommended [9]. Notably, no new alternatives have been proposed since the author's previous review of annuloplasty published over 7 years ago [10]. All of them have both advantages and disadvantages, making it difficult to judge which method is better over others, and each surgeon is currently focusing on their favourite type. The lack of studies comparing each method is probably why surgeons remain stuck in this never-ending labyrinth of aortic valvuloplasty.

In these turbulent times, Jarral et al. [6] should be congratulated for publishing their experience with 71 cases over 6 years in this issue of EJCTS, one of the largest single-institutional experiences with internal rigid ring annuloplasty. Early results are excellent without in-hospital mortality in spite of many concomitant procedures. Freedom from reoperation is also favourable with 94% at 3.9 years. However, unfortunately, it is still a retrospective, single-institutional, single-arm study. Readers can only judge the merits or demerits of this method by comparing its results with historical cohorts. Furthermore, the short mean follow-up period of 3.9 years does not allow us to estimate the true effect of this ring. A common concern among surgeons is fixing a rigid ring adjacent to the delicate valve leaflets. Indeed, 3 of the 4 repair failures were due to ring dehiscence. The geometry of commissural posts of this ring that flare outward by 10° might be one of the causes of this ventricular septal defect. Subcommissural suture to fix this ring might be another cause. Finally, the patients who had undergone this operation did not have an extremely enlarged annulus (not over 30 mm but median 27 mm). Patients with such a large annulus should benefit from this ring, but its effectiveness is unknown. Even so, only rings up to 25 mm are currently available.

So, what is the ideal aortic annuloplasty ring? Briefly, it is one that restores the normal geometry and function of the aortic annulus. With the recent advances of imaging technology, it has been revealed that the aortic annulus has an oval shape on a 3D plane. Currently applied suture annuloplasty and flexible ring annuloplasty cannot restore the elliptical shape, so in that respect, this rigid ring, which restores the near-normal morphology of the aortic annulus, makes sense. On the other hand, the aortic annulus expands and contracts with the cardiac cycle, and in this respect, the rigid ring is non-physiological, and suture annuloplasty and flexible ring annuloplasty are preferred. Therefore, would not an external semi-rigid ring be the ideal ring to restore the geometry and function of the aortic annulus without affecting the delicate leaflets? I cannot help but hope that the day will come soon when such a ring will become commercially available and many surgeons will be able to escape from this seemingly endless labyrinth.

Anyway, I would like to pay tribute to the efforts of their team, who concentrated on 1 ring and applied it to 71 cases over a period of 6 years, achieving satisfactory results. There is no doubt that their data will serve as a valuable milestone and will be used for comparison with other annuloplasty methods in the future. We hope that they will continue to use this ring in more cases, analyse the causes of failure in detail, aim to further improve clinical outcomes with technical modifications and illuminate the path that will lead us out of this labyrinth.

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