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Nappi et al. Vessel Plus 2021;5:40 https://dx.doi.org/10.20517/2574-1209.2021.06 Page 7 of 20

three-quarters had a degenerated mitral bioprostheses. For patients who underwent TMViR/valve related to
MAC disease, the estimated survival rate was 78% at 30 days. Instead, for those who received TMViV for
degenerated bioprosthetic mitral valve, the survival rate was 95% at 30 days [95% confidence interval (CI):
70%-86% vs. 92%-97%; P = 0.008]. Finally, the survival rate was 68% in patients who had transcatheter mitral
valve therapy ViR/ViV in MAC group compared to the rate of 86% in those who were managed with
transcatheter mitral valve therapy for failed bioprosthetic mitral valve at 1-year follow up (95%CI: 58%-78%
vs. 81%-91%; P = 0.008) [14,15] .

[23]
Hu et al. , in a recent systematic literature review, analyzed the outcomes of 245 patients who underwent
TMVR (172 TMViV and 73 TMViR) surgery for degenerated bioprostheses and failed annuloplasty ring
from 2009 to 2018. The mean age of all candidates for TMViV therapy was 73 ± 12 years, with a mean STS
score of 15.6% ± 13.5% and mean LVEF or 46.7% ± 14.1%. In this review, the technical success rate was
93.5% and the operative mortality was 5.7% with no significant differences between the two groups (5.2%
TMViV vs. 6.8% TMViR). In the entire study, left ventricular outflow obstruction were observed in 4 (1.6%)
patients: 0 (0%) in the TMViV group and 4 (5.5%) in the TMViR group.

[31]
In a recent review with a 5-year follow up, Cheung et al. reported 23 consecutive patients with
degenerated mitral bioprosthesis, who were successfully treated using TMViV. Patients received Edwards
SAPIEN-type balloon-expandable valves with a left ventricular apex approach. The success of the device was
100% and no cases of valve related malposition or embolization occurred .
[31]

As demonstrated by the reported data and the cited studies, despite the evidence of low intraoperative and
postoperative mortality and low incidence of major bleeding and stroke, the main concern with the use of
TMViV-T, besides the possible need for a reoperation, is the increased risk of complications from LVOT
obstruction and death related to congestive heart failure.

Eleid et al. [14,15] showed that LVOT obstruction significantly increased in patient with higher ejection
fractions (66 ± 6 mmHg vs. 56 ± 12 mmHg; P = 0.002). This risk is even higher in TMViR or TMV-in-MAC
recipients than in those who had TMViV procedures. It is important to point out that the majority of
patients who had minimal symptoms related to LVOT obstruction were managed conservatively, showing
transvalvular mitral gradients decreasing over time. Nevertheless, in some cases, patients who received
TMViVR or TMV-in-MAC developed a critical obstruction related to displacement of the systolic anterior
mitral leaflet in the left ventricular outflow tract resulting in irreversible impairment of cardiac function
with death due to the onset of congestive heart failure. However, the incidence of severe LVOT issue and
other complications can be notably decreased by careful patient screening [24,33-35] .

Another concern is related to the choice of the appropriate size of the implant, which remains a matter of
debate. We mainly adopt an oversizing of 5%-10% compared to the pre-existing prosthesis. The reference
considered is the internal diameter reported by the producer, so, for patients who had a prosthesis with an
internal diameter of less than 21.5-mm, a 23-mm SAPIEN valve is preferred. The advantage offered by
oversizing lies in a greater security for anchoring the device when it is inserted inside the sewing ring.
Furthermore, this choice has proved to be of great use in reducing the risk of paravalvular leakage.
However, the risks of extreme oversizing remain to be considered and should be avoided. In fact, a severely
under-expanded device can lead to various drawbacks including an increase in the transvalvular gradient, a
non-optimal coaptation of the leaflet and a compromised valve durability [14,15] . Ultimately, a considerable
contribution has been offered by the standardized use of cardiac computed tomography, which has proved
to be fundamental in assessing the risk of LVOT obstruction and determining the degree and distribution of