Minimally invasive mitral valve repair: for every patient, for every surgeon or still a work in progress?

J Thorac Dis 2020 | http://dx.doi. org/10.21037/jtd.2020. 02.39 The history of minimally invasive (MI) cardiac surgery started with coronary artery bypass surgery (1), but the term “minimally invasive” was defined as “an intervention that does not require median sternotomy or the use of cardiopulmonary bypass”. The subsequent application of the same concept to mitral valve (MV) surgery changed the meaning of MI, from “no sternotomy, no cardiopulmonary bypass” to “no full sternotomy”. Partial sternotomy, in fact, has been and is still used and cardiopulmonary bypass, of course, is part of the procedure. In general MI became minimally access. But a sentence in the last paragraph of the paper from Calafiore et al. (1), written in 1996, sounds as a prophecy: “Future generation of cardiac surgeons, especially those in training, will have to become familiar with minimally invasive cardiac procedures, especially MICAB. ” The interest in MI coronary artery bypass is again increasing (2,3) and MI valve surgery is continuously expanding. The trend in MIMV surgery has been studied by Paparella et al. (4) in a multicenter study. They found that the MI approach became more frequent from 2011 (27.5%) to 2017 (71.7%), with a similar early mortality in subjects paired by propensity score. Cardiopulmonary bypass time and cross-clamping time reduced progressively over time. However, if the benefits of MIMV surgery in terms of reduced intensive care and in-hospital stay, reduced rate of atrial fibrillation, less transfusion rate, lower readmission rate are now clear (4-7), a more comprehensive analysis identifies a few weak points. Most of the cases are concentrated in a few Institutions, where the results are optimal (8). On the other side a low surgical volume is considered to affect the quality of the surgical results (8,9), as low volume Centers concentrate most of the complications. An analysis of the trends in less invasive MV operation in US showed that 26% of the Centers performed at least one procedure per year, but the median was 3 (10). Some complications appeared to occur more in MIMV surgery, as bleeding (9,10), aortic dissection (11), stroke (10,11), phrenic nerve palsy (11) and in a recent paper it has been reported that the ejection fraction was reduced in patients who underwent MIMV repair if compared with propensity matched pairs undergone median sternotomy (12). However, most of these complications are related to the most critical part of MIMV surgery: the learning curve. A study indicated that 75 to 125 procedures were necessary to master the technique and that to maintain the skill is necessary at least 1 case per week (13). Another study reported that the number of operations necessary to overcome the learning curve was 60 for MV replacement and 90 for MV repair (14). It is then clear that the limit to the expansion of the technique is not only to perform the surgery or to choose the patient, but also to maintain the necessary expertise, impossible in low volume Centers. As a consequence, a MI approach, even if used since long time (15) to correct both degenerative (4) and functional (16) mitral regurgitation (MR), still is not the procedure of choice for MV repair. Editorial Commentary