## 4 Discussion
Conversely, the risks related to more aggressive techniques with radical debridement and reconstruction of the annular anatomy are well recognized, with non-negligible mortality and major morbidity, i.e., heart block requiring permanent pacemaker insertion, perioperative myocardial infarction and hemorrhagic complications at the level of the atrioventricular junction or proximal left ventricular free wall, often uncontrollable and fatal [31; 32; 33]. The recent adoption of the so-called microinvasive options, such as transcatheter prosthetic MV implantation procedures may represent an appealing alternative, particularly in high-risk patients, but to date outcome is suboptimal and indications are anatomically stringent, particularly in case of a relatively small left ventricle and a narrow nitroaro aortic angle, which imply a hazard of left ventricular outflow tract obstruction. In this scenario, the earliest experience with severe MAC was collected from the MAC Global Registry and reported a 30-mortality rate of 25% [34]. In a systematic review by [PERSON] et al., on 354 patients with MAC disease undergoing trans-septal and trans-apical valve-in-valve, the risk of left ventricular outflow tract obstruction was 11.2%, the incidence of at least moderate post-procedural mitral regurgitation was 4.1%, the rate of device embolism was 3.7%, and the risk of reintervention was 16.7%. The reported 30-day and 1-year mortality rates were 23%, and 43% respectively [35]. Our surgical practice in patients with MV disease and MAC is, whenever possible, to prefer repair techniques, and this is usually feasible in cases of mild to moderate MAC without significant leaflet involvement. In our series, however, repair was feasible only in 6/27 patients (22%), always with implantation of a complete prosthetic ring, while posterior leaflet resection and artificial chordal positioning were performed in three and in two patients, respectively. In case of valve replacement our technique of choice includes the least debridement of annular calcifications in order to drive the sutures and to achieve a good seating of the prosthesis. Aggressive decalcification is seldom necessary, avoiding time-consuming annular reconstruction coupled by a reduced hazard of atrioventricular disruption, coronary injury and, ultimately, intraoperative death. Besides, minimally invasive techniques are more straightforward and less cumbersome with this approach. The extent of the annular calcium bar impacts the feasibility of MV repair. In case of extensive or near-circumferential MAC or leaflet involvement, the MV flexibility is severely impaired and the chances of a durable repair are jeopardized. In our population, severe and moderate MAC grading was reported in 11 (41%) and 13 (49%) patients, respectively, whereas involvement of one or both MV leaflets was observed in 48% and 52% of the cases. Not surprisingly, as already stated, the repair rate was only 22% (6/27). Traditionally, MAC has been primarily addressed through a conventional full sterotomy. Nevertheless, the promising results reported by minimally invasive cardiac surgical programs have drawn the attention toward more complex cases, including MV disease with MAC. The benefits of a minimally invasive approach are particularly evident in elderly or frail patients, as well as in case of prior cardiac operations with the inherent risks of re-sternotomy and coronary bypass graft injury, if present. Besides, MV exposure may be more favorable with a lateral approach in patents with a relatively small left atrium. In our experience with minimally invasive MV surgery during the last two decades, this case series indicates the feasibility and effectiveness also in patients with MAC with low perioperative mortality and rate of complications.