Aortic valve repair: a glimpse into the future

As the repair of the aortic valve emerges as a more standardized and reproducible discipline, it is interesting to glance back at its past and venture a glimpse into the future. In doing so, it is tempting to examine the journey of mitral valve repair as it has evolved from an enigmatic art practised by a handful of masters to an algorithmic science applied by many in daily practice. The journey of mitral valve began with a few pioneers who systematically and persistently applied reparative techniques to correct mitral insufficiency. A critical milestone was the development of the classification of mitral valve insufficiency by Carpentier [1], which provided the much needed common language and enabled communication among cardiologists, echocardiographers and surgeons. The earliest repairs of the mitral valve were simple suture annuloplasties, followed later by the development of a variety of materials and techniques to facilitate annular remodelling and stabilization. This was followed by leaflet repair techniques which continue to evolve and engender debate among surgeons today [2]. With the accumulation of experience and clinical data, comparative studies examining the outcome of repair versus replacement were instrumental in establishing mitral valve repair as the preferred treatment for mitral valve insufficiency [3]. Perhaps, the slowest step in the development of mitral valve repair was the dissemination of the surgical techniques from a few experts to the worldwide community of surgeons—a process which continues to this day. Notably, this journey of mitral valve repair, from its earliest application to its establishment as a Class I indication for the treatment of mitral insufficiency, took over three decades. The journey of aortic valve repair to date bears significant resemblance to that of mitral valve repair. The preservation of the normally functioning aortic valve in the context of aortic root pathology was perhaps the first important milestone in aortic valve repair. The valve-sparing techniques of reimplantation and remodelling pioneered by David and Feindel [4] and Yacoub et al. [5] were the first annuloplasties of the aortic valve, compelling surgeons to better understand the anatomic and functional relationships of the aortic valve annulus and cusps. In the last decade, we have seen the emergence of a variety of leaflet repair techniques including free margin plication, free margin resuspension, triangular leaflet resection and pericardial patch augmentation [6, 7]. In recent years, we have also seen the emergence of a classification system for aortic insufficiency [8] that provides us with the vocabulary with which to converse about aortic valve repair, much like the Carpentier classification did for mitral valve repair. Outcome data are starting to emerge, and a number of studies now report follow-up beyond 10 years. Published studies have already reported good repair durability and a low rate of valve-related complications with aortic valve repair [9, 10]. Despite the similarities, important aspects of the aortic valve are different from those of the mitral valve. One reason for the later development of aortic valve repair techniques compared with mitral valve repair is that the most commonly encountered pathology of the aortic valve is degenerative calcific stenosis, which offers little choice to the surgeon except to resect and replace the valve. Secondly, in contrast to the mitral valve, surgeon's' view of the aortic valve is from its outflow side, making it virtually impossible for surgeons to visually assess and test the valve in its pressurized state. Echocardiographic and anatomic assessment of the aortic valve is, therefore, critical for successful aortic valve repair. Thirdly, the functional aortic annulus is not a single entity, but rather consists of two distinct anatomic structures, namely the ventriculo-aortic junction (VAJ) and the sinotubular junction (STJ), both of which play an important role in the normal valve function. Thus, annuloplasty of the aortic valve requires attention on both of these components. As the preservation and repair of aortic valves matures as a discipline, there are several important challenges and opportunities that lie ahead. First, there is a need to expand the repertoire of surgical techniques available for aortic valve repair. One such area is the development of materials and techniques for stable annuloplasty of the aortic valve. Currently, the most stable method of annular stabilization, commonly used in the context of aortic root pathology, is a valve-sparing root replacement procedure using the reimplantation technique, which serves to stabilize both the VAJ and the STJ. However, techniques and materials to address VAJ dilatation in the setting of a non-dilated root, often seen in patients with bicuspid aortic valves, require further refinement. Our group, along with others, has suggested novel approaches that are in the early phase of development. Another such area is the development of materials for cusp augmentation and reconstruction. Currently, autologous or bovine pericardium is the most commonly used material for the replacement of cusp tissue. However, both are associated with limited longevity of valve repair [10]. The ideal material would endure the haemodynamic stresses of the aortic valve without degeneration or calcification, would not trigger an immune response, be available off the shelf and have excellent intraoperative handling properties. The next important frontier in the advancement of aortic valve repair is the careful conduct of long-term, outcome studies. Important limitations of the existing literature in this context include mostly single-centre, single-surgeon studies, the variation in the surgical techniques employed, inadequate description of the population studied, loss to follow-up and incomplete or inadequate reporting of valve-related events. Furthermore, as more data accrue, outcomes of aortic valve repair need to be compared with those of aortic valve replacement with mechanical valves, bioprosthetic valves and the pulmonary autograft. It is likely that the greatest benefit of valve preservation and repair will be realized in younger patients and will be in the form of reduced valve-related complications. Perhaps, the slowest, most labour-intensive step in the development of mitral valve repair was and continues to be the dissemination of surgical techniques and experience around the world. A recent study estimated that among surgeons performing mitral valve surgery in the USA, the average rate of mitral valve repair was 41% [11]. This challenge will be equally significant for the development of aortic valve repair. The time-honoured surgical tradition of teaching by demonstration and mentorship goes a long way to impart the necessary surgical techniques and judgement. However, the process is slow and the impact is often limited to a small number of individual surgeons. Adjunctive tools to facilitate education should be considered, including the use of animal or cadaveric models and computer simulation. Lastly, advances in technology and imaging now allow for the construction of finite element models of the aortic valve based on real patient data from echocardiograms. Surgical techniques can then be implemented within these models to assess and predict the outcome of certain anatomic manipulations. This ‘virtual surgery’ platform can facilitate patient-specific surgical planning and potentially make the application of aortic valve repair a more predictable endeavour. Aortic valve repair is at an important crossroads in its development. As the techniques become more reproducible and better established, it is increasingly being applied, particularly in younger patients. On the other hand, while the current data on repair durability and valve-related complications look quite promising, comparative studies examining outcomes between aortic valve repair and replacement are limited. The question of whether aortic valve repair will become the preferred treatment modality for all patients with aortic insufficiency remains unanswered. However, a quick review of the history of mitral valve repair reveals that important milestones in the development of aortic valve repair have already been achieved as it evolves into a viable alternative to aortic valve replacement in patients with aortic insufficiency.

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