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Page 6 of 10 Scotti et al. Vessel Plus 2021;5:6 I http://dx.doi.org/10.20517/2574-1209.2020.68

(2) an adequate annular size, which must not be too small not to allow safe anchoring and not too wide to
increase the risk of LVOT obstruction;
(3) the LV function, which could be greatly reduced after TMVRpl;
(4) the native leaflets and the eventual annular calcifications to find the best implant site, which should be
as atrial as possible.

As the transfemoral approach is under development, the patients to be screened must be able to tolerate
transapical access. This condition may constitute a great limitation, especially in patients with SMR who
have remodeled LVs or ischemic scars.

Structural valve deterioration is a great concern for TMVRpl. The systolic pressure gradient generates a
significant mechanical stress on the bioprosthetic mitral valve, resulting in a more frequent degeneration if
compared to the aortic counterpart. This rate is increased even more by the young age of the patients (~ 10 years
[17]
younger than recipients of aortic valves) . Indeed, greater hemodynamic shear stress, differences in
calcium deposition, and residual leaflet antigenicity contribute to a higher tendency of valve degeneration
[18]
in younger patients .
Another factor to be considered is the feasibility of anticoagulation treatment to avoid device thrombosis.
[19]
This complication was reported in 3% of patients in TMVRpl studies , which adopted a minimum
regimen of three months of anticoagulation mimicking the recommendations from current guidelines
regarding conventional surgical mitral valve replacement.

A careful analysis of the enrollment criteria of the TMVRpl trials allows us to identify the patient to be
denied or offered this therapy [Table 1]. The presence of a LV (LV end diastolic diameter > 70 mm, LVEF
< 30%) or right ventricle (RV) dysfunction, hypertrophic obstructive cardiomyopathy, and restrictive or
constrictive cardiomyopathy represent common exclusion criteria [Figure 3]. Comorbidities such as severe
chronic kidney disease requiring dialysis, significant coronary artery disease, and bleeding or thrombotic
disorders are further unfavorable factors. Regarding the valve apparatus, predicted LVOT obstruction,
severe mitral stenosis, fused commissures, prohibitive mitral annulus calcifications, and vegetations or
valvular masses have to be avoided. The most important features that favor TMVRpl over TMVR are
represented by the prediction of a suboptimal MR reduction with the latter technique and some of the
TMVR exclusion criteria such as multisegment or commissural disease, perforations, or clefts. For the
reasons outlined above, the ideal patient should have a good LV function (LVEF > 30%) in the absence of
scars or remodeled LV walls that could be irreversibly damaged by a transapical access.

FUTURE PERSPECTIVES
Currently, a repair-first strategy is the transcatheter way to go for patients with severe MR. The lessons
learned from the surgical experience and the paucity of data on TMVRpl make this approach a second
[20]
choice . A percutaneous repair respects the complex anatomy and physiology of the mitral valve. The
preservation of the valvular and subvalvular apparatus leads to LV and RV reverse remodeling with
improved functional performance [21,22] . However, the technological progress in transcatheter valves could
increase the appeal of TMVRpl therapy if a valve capable of adapting to such variable anatomies was found.
This hoped-for result would mean having a device less technically demanding, with great versatility and
more predictable results in terms of MR reduction.

Transseptal delivery systems for TMVRpl are emerging and will replace the current transapical approach,
which is burdened by an increased risk of peri-procedural complications.