**5. Technical considerations**

The first few TMVR procedures were performed using a surgical transapical [6, 7] or open trans-atrial [8, 9] approach, but subsequent reports described successful implantation with a completely percutaneous trans-femoral transseptal approach [10–12]. Transseptal access has been the default access in ViV and ViR in the MITRAL trial, while both transseptal and trans-atrial access have been equally used in ViMAC [16–18]. All-cause 30-day mortality in ViMAC was 16.7% (trans-atrial, 21.4%; transseptal, 6.7%; transapical, 100% [n = 1]; p 0.33) and 1-year mortality was 34.5% (trans-atrial, 38.5%; transseptal, 26.7%; p = 0.69) [18]. These mortality rates are relatively higher than other transeptal or transapical procedures; as studies have shown that the 30-day and 1-year mortality rates were 3.6% and 23.2% for

*Transcatheter Mitral Valve Replacement: Evolution and Future Development DOI: http://dx.doi.org/10.5772/intechopen.98953*

patients undergoing transseptal transcatheter edge-to-edge repair using MitraClip for secondary mitral regurgitation, and the 30-day and 1-year mortality rates were 8.4% and 25.4% for transapical TAVR [22, 23].

Because the mitral annulus is larger in size compared to aortic valve annulus, TMVR requires larger devices, including prosthesis and delivery systems [10]. Mitral annular calcifications are less common compared with aortic valve calcifications, and their presence may condition the implant of a transcatheter mitral prosthesis. For this purpose, the role of TMVR in presence of considerable annular calcification is less clear, as shown in the MAC (mitral annular calcification) Global Registry, which demonstrated that TMVR was feasible in MAC but associated with relatively high early and midterm mortality at 1 year, although patients who survived at 1-year follow-up had sustained improvement of symptoms [4, 5]. Similarly, the MITRAL trial showed relatively high 1-year mortality in ViMAC patients, but transeptal ViMAC showed promising results with 30-day mortality lower than the predicted STS score, however mortality rates in this population remains higher than other transeptal procedures, including transcatheter edge-to-edge repair using MitraClip [1, 2, 18].
