Minimally invasive endoscopic mitral valve repair—the new gold standard for degenerative mitral valve disease

Almost 2 decades ago, the first successful case series demonstrated feasibility and safety of minimally invasive access mitral valve surgery (MIMVS) [1]. Subsequently, larger series reported longer-term follow-up with durable repair results for degenerative mitral valve pathologies with freedom from recurrent mitral regurgitation of at least 92% at 5 years [2]. Despite these convincing data, minimally invasive access for mitral valve repair is still under debate within the cardiac surgical community and not standard of care in all healthcare systems. In this issue of the European Journal of Cardiothoracic Surgery, Bonaros et al. [3] share their experience with a well-established MIMVS programme. The reported safety and functional outcome data are impressively good. Even more interesting are the surgical details discussed and the procedural changes in their practice over an almost 20-year time span including the addition of routine preoperative Computed tomography scans (CT) scans, the adoption of a non-rib-spreading 3D endoscopic approach and the trend from resection techniques towards leaflet preserving repair techniques including the use of artificial chordae. In many centres dedicated to minimally invasive mitral valve surgery, a development or refinement of surgical techniques could be observed over the last decade. In the early years, most programmes used a video-assisted ‘mini’-thoracotomy approach that also allowed for direct vision of the valve. The availability of high definition 3D endoscopy allowed for a further minimization of the surgical access including micro-thoracotomies, periaureolar and non-rib-spreading access while providing high-resolution 3D visualization of the mitral valve. Despite high patient acceptance, the evidence proving superiority of the minimally invasive access compared to sternotomy is largely missing. Few underpowered randomized controlled trials and meta-analyses did not find significant differences between the groups with regard to early mortality or long-term survival [4, 5]. However, morbidity seems to be significantly reduced when compared to a classic sternotomy approach (shorter intensive care unit stay, less transfusions, shorter ventilation times, etc.). On the downside, MIMVS will typically lead to slightly longer procedure times, cross-clamp and cardiopulmonary-bypass times [4, 5]. More importantly, MIMVS has been associated with an increased stroke rate, which was reported in some early studies [6] and has long been recognized as the potential ‘achilles heel’ of minimally invasive mitral valve surgery. In this context, the reported stroke rate from the Innsbruck group with 0.1% only deserves a closer look. It is obvious that the risk for stroke is not associated with a smaller surgical access per se but may be linked to the potential risks of retrograde cardiopulmonary bypass perfusion. Bonaros and colleagues demonstrated that, with meticulous preoperative planning based on CT angiography, this potential risk can be overcome [7]. In case of calcified femoral and iliac arteries or even more importantly abdominal aorta with thrombotic debris or ulcerations the group opted for central cannulation via a full or partial sternotomy. With this strategy, they were able to achieve an impressively low stroke rate. An alternative vascular access for arterial cannulation is the axillary artery, which can avoid the problems associated with femoral cannulation in this setting. Another potential shortcoming of MIMVS is the learning curve that is typically associated with any surgical procedure [8]. The Innsbruck group has to be congratulated for not only having served the surgical community as a training centre, and offering courses for minimally invasive valve surgery but also for building a training program. The applied pilot/co-pilot concept is largely facilitated by endoscopic visualization and seems very well suited to safely train new surgeons in a stepwise manner. Bonaros and colleagues used different ‘combined end points’ to assess the outcome. While ‘reoperation free survival’ or ‘perioperative safety’ is variables often described in surgical literature, the definition of ‘operative success’ is an interesting concept. Interestingly, the only protective factor for operative success was found to be the utilization of artificial chordae compared to resection techniques. In contrast, a randomized trial comparing a classic resection approach with neo-chordae techniques did not find a significant difference in repair success, although neo-chordae were associated with significantly larger length of coaptation [9]. The non-resection neo-chordae technique that has been adopted by many groups is well suited for a 3D endoscopic approach. As it is more forgiving, it might be easier to teach to new surgeons. The definition of ‘operative success’ used by the Innsbruck group follows the principles of value based care and goes well beyond the definition of a ‘successful repair’ or the classic ‘safety’ end points. It takes a patient perspective for summarizing the most important outcome variables. This is in contrast to more technical definitions that are applied to transcatheter mitral valve repair. The Mitral Valve Academic Research Consortium defines ‘procedural success’ as reduction of mitral regurgitation to optimal or ‘acceptable’ in addition to other safety end points [10]. Whereas ‘optimal’ matches the surgical definition of a good repair with either trace or none residual regurgitation, an ‘acceptable’ outcome per this definition also includes moderate (2+) mitral valve insufficiency—which is known to impact durability of the ‘repair’ mid-term. Therefore, it is important to define the quality of surgery and to report outcomes accordingly. In summary, the paper of Bonaros and colleagues is published in a timely manner to once again define the gold standard for mitral repair that can be achieved with minimally invasive endoscopic mitral valve surgery especially in low-risk patients suffering from degenerative mitral valve regurgitation.