**3. Scientific evidence supporting TMVR**

The scientific evidence supporting TMVR is based on observational data, mostly from registries, in North America and Europe [1, 4–15], summarized in **Table 1**. Several studies showed data on outcomes of mitral ViV, ViR, ViMAC from single or multi-center registries; with consistent results demonstrating overall better outcomes for mitral ViV procedures compared to mitral ViR and ViMAC [1, 4–15].

The role of mitral ViV, ViR, and ViMAC has been evaluated in a prospective early feasibility clinical trial, the MITRAL trial (Mitral Implantation of Transcatheter Valves, NCT 02370511), which is the first prospective study assessing outcomes of TMVR in all of the three separate subtypes. The results of the trial have been recently published [16–18].



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

#### **Table 1.**

*Summary of observational TMVR studies with their major outcomes.*

In the MITRAL trial, in which 30 patients undergoing transseptal mitral ViV were enrolled between July 2016 and October 2017, technical success was achieved in 100% of cases with 30-day all-cause mortality of 3.3%, which remained unchanged at 1 year. At 1-year follow-up, the vast majority of patients were in New York Heart Association (NYHA) functional class I or II [16].

Similarly, in the MITRAL trial assessing patients undergoing transeptal mitral ViR, 30 patients were studied with results showing technical success of 66.7% (driven primarily by need for a second valve in 6 patients), all-cause mortality of 6.7% at 30 days and 23.3% at 1 year. Similar to ViV study, the vast majority of patients were in NYHA class I or II at 1 year [17].

MITRAL trial assessed ViMAC by prospectively enrolling 31 patients and was challenged by a high proportion of patients with threatened left ventricular outflow tract (LVOT) obstruction. As such mitigation strategies were devise in the form of alcohol septal ablation and trans-atrial valve implantation accompanied by anterior leaflet resection. As such as high proportion of patients received transatrial TMVR (48.4%), while transseptal access was used in 48.4%, and transapical access 3.2%. Technical success was achieved in 74.2% of cases, overall 16.7% (trans-atrial, 21.4%; transseptal, 6.7%; transapical, 100% [n 1/4 1]; p = 0.33) all-cause mortality rate at 30 days and 34.5% (trans-atrial, 38.5%; transseptal, 26.7%; p = 0.69) mortality at 1 year. Similar to ViV and ViR study, the vast majority of patients were in NYHA class I or II at 1 year [18]. Importantly, this trial introduced preemptive alcohol septal ablation as a mitigation strategy to prevent LVOT obstruction [18].
