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Page 4 of 20 Nappi et al. Vessel Plus 2021;5:40 https://dx.doi.org/10.20517/2574-1209.2021.06

TMViV-T includes a transapical, transatrial or transseptal approach. The transapical approach is performed
by practicing a small anterolateral thoracotomy in the fifth or sixth intercostal space which is used to access
the pericardial space near the left ventricular apex. At this level, the transcatheter heart valve (THV) delivery
system is introduced. The advantage of this approach is due to the anatomical peculiarity that allows direct
access to the entire mitral apparatus aimed at the coaxial retrograde deployment of the transcatheter heart
valve in patients presenting with a failed surgical mitral bioprosthesis. Instead, the transatrial approach
technique is performed through a small anterolateral thoracotomy which allows the antegrade deployment
of the transcatheter heart valve device. Finally, the transseptal approach is achieved with an initial access
through the femoral vein, which allows the catheters and delivery system to progressively advance towards
the left atrium. A transseptal puncture is performed, allowing for the deployment of the antegrade
transcatheter heart valve [18,26] .

The main advantage of the transseptal approach is avoiding a thoracic incision, which offers a quick post-
procedural recovery after mechanical intervention. Moreover, its indication is suitable in patients with
severe chronic lung disease or in those who were managed with multiple sternotomies [8,18,26,28] .

The preferred approach was the transapical access (70.1%) over transseptal (24.4%). It is important to note
that in-hospital and 30-day mortality was much less common than their STS PROM (8.5% vs. 11%), while
1.4% of patients experienced postoperative left ventricular outflow tract obstruction. In addition,
considering the fragility of patients treated with this type of mechanical intervention, the post-procedure
morbidity was low. A postoperative left ventricular outflow tract obstruction occurred in very few patients;
similarly, the rate of stroke or need for dialysis was low in recipients of TMViV-T. Repeat mitral valve
surgery during hospitalization was not required for any patient. Considering that 83.7% of the patients had
echocardiographic control available, moderate to severe mitral regurgitation occurred infrequently and the
measured transvalvular mitral gradients were low. Evidence based on early outcomes in this group of high-
risk patients, for whom repeat open mitral valve surgery was avoided, is encouraging. Therefore, TMViV-T
can be offered as an effective treatment option for this category of patients [18,26-28] .

Clinical evidence and technical evolution using transcatheter mitral valve-in-valve therapy
The international registry for transcatheter mitral valve replacement (TMVR) was established with the aim
to treat patients with degenerated mitral bioprostheses and failed annuloplasty rings who are suitable to
receive the transcatheter mitral valve-in-valve therapy. All patients who were subsequently recruited, with a
mean age of 72.5 years and a mean STS score of 8.9% ± 6.8% [Table 1], constitute the TMVR registry, which
serves as a multicenter observational study. It was due in November 2015 with a total of 25 centers from
Europe and North America working to implement and improve the registry. In total, 248 patients were
included to receive a mechanical intervention on the mitral valve through transcatheter-based therapy. Of
these, 176 patients (71%) were considered to receive a TMViV for a degenerated mitral bioprosthetic valve,
whereas 72 patients (29%) had TMViR due to failed annuloplasty rings [8,19,27,29,30] .

Considering the cohort, we noted a relatively low rate of procedure-related death (n = 3; 1.2%), conversion
to conventional surgery (n = 5; 2%), valvular embolization (n = 4; 1.6%) and left ventricular perforation
occurred (n = 1; 0.4%). Across the group, left ventricular outflow obstruction occurred in 8 (2.3%) patients,
but there was no difference between patients receiving TMViV (4; 2.3%) or those undergoing TMViR (4;
2.3%). Patient-related successful procedure was achieved in 92.3% of device recipients; however, a
significantly lower technical success rate was noted in patients who were managed with TMViR than in
those who had TMViV. Other significant differences included reintervention for paravalvular leak that
occurred more frequently in patients who were managed with TMViR compared to those who underwent