## 4 Discussion  
MAC requires technically demanding surgery, increases operative risk, and impairs the repair feasibility in patients with degenerative MV disease [16; 17; 18]. Several surgical techniques have been described to tackle this issue with varying results. These include isolated leaflet repair or resection, or implantation of artificial ePTFE chordae with or without annuloplasty [19; 20], edge-to-edge MV repair [21], valve replacement with no annular calcium debridement securing the prosthesis inside the calcified annulus [22], intra-atrial insertion of a mitral prosthesis eventually with Dacon or pericardial patch interposition to form an external skirt or prosthetic neo-annulus [23; 24], partial debridement of the calcific bar [25], en bloc decalcification and annular reconstruction with Dacon or pericardial patch [16], and ultrasonic debridement of the calcification [26]. Finally, extra-anatomical left atrial to left ventricular apex bypass with a valved conduit has been described by the Mayo Clinic team as an extra-anatomical solution in patients with extensive MAC [27], mimicking a technique originally performed during the Eighties at the Bambing Gesi Hospital in Rome to correct congenitally hypoplastic atrioventricular valve stenosis in children [28]. Clearly, the strategies that avoid altogether the manipulation of the MV annulus and that thus do directly address the MAC are technically more straightforward. Unfortunately, successful repair with no annuloplasty is applicable only in a minority of patients and, paradoxically, in those with less severe MACs and with minor leaflet involvement. Similarly, edge-to-edge procedures can be very easy and not time-consuming to perform, but almost invariably at the expense of some degree of residual MV regurgitation, in analogy to transcatheter edge-to-edge repair with MitraClip(tm) technology (Abbott Vascular, Abbott Park, IL, USA). Conversely, intra-atrial fixation of a MV prosthesis might appear a clever and appealing solution, but may not uniformly allow secure anchoring in an ectopic position and also often determines implantation of a smaller valve because the annular orifice \begin{table}
\begin{tabular}{l c} \hline \hline FU iEOA (cm\({}^{2}\)/m\({}^{2}\)) & 1.44 \(\pm\) 0.29 \\ Follow-up (days) & 271 (102–671) \\ \hline MV: mitral valve TV: tricuspid valve; RAP: retrograde arterial perfusion; EAC: endo-aortic clamp; TTC: transt thoracic clamp; CPB: cardio-pulmonary bypass; IQR: interquartile range; SD: standard deviation; ICU: intensive care unit; FU: follow-up; iEOA: indexed effective orifice area. Data are expressed as median (IQR), mean \(\pm\) SD, or n (%). \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont_. is blocked by the MAC, with consequently higher postoperative transvalvular gradients. Although successful off-label implantation of an upside down 23 mm or in extreme cases 21 mm St. Jude Regent (St. Jude Medical, Inc., St. Paul, MN, USA) aortic mechanical prosthesis in the mitral position has been reported, predominantly in smaller size women with MAC or prior mediastinal radiation therapy [29], gradients may be a critical issue and often imply clinically relevant patient-prosthesis mismatch with persistently elevated left atrial and pulmonary pressures and reduced long-term survival [30]. Mid- or long-term results with extra-anatomical bypass still await to be validated. A somewhat more conservative approach to MAC with no or minimal annular debridement and a prosthesis secured to the near-intact calcium bar may offer reliable results, but should be balanced with the hazards of periprosthetic leak, circumflex artery injury and atrioventricular heart block, related to the sutures being driven through or around the calcified material, and with the difficulties in implanting a prosthesis of adequate size.