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Annibali et al. Mini-invasive Surg 2022;6:12 https://dx.doi.org/10.20517/2574-1225.2021.101 Page 11 of 16

leads to heart failure because of increased transvalvular gradients (1%-3%) [79-81] .

In recent studies, subclinical leaflets thrombosis has been identified in a quarter of patients on antiplatelet
therapy, and there is evidence that oral anticoagulants prevent and can effectively regress leaflets thrombosis
with a significant reduction of valve gradient, although subclinical leaflets thrombosis may regress
spontaneously [77,82,83] . Some observational studies have shown an increase in thromboembolic events in
patients with subclinical leaflets thrombosis, but this has not been confirmed in the GALILEO trial and
other studies. The PARTNER-3-CT sub-study showed only a slightly higher valvular gradient when there
[84]
was present subclinical leaflets thrombosis at both 1 and 12 months .
ViV TAVR patients need to be considered at high risk of THV leaflets thrombosis for several reasons. In the
case of a very low implant, the THV will work with suboptimal hemodynamics with altered flow patterns,
creating a milieu for leaflet degeneration and, possibly, for thrombosis. Conversely, in the case of a very
high implant, which is requested in ViV procedures inside small surgical valves in order to achieve the
lowest possible gradient, there are ex-vivo bench-test data showing produced blood flow in some regions
between the two prostheses [75,85] . From computational study with flow fields, one of the hypothesized
mechanisms underlying this phenomenon is considered to be the geometric confinement of TAVR leaflets
by failed bioprostheses, which promotes the slowing of blood flow and promotes leaflet thrombosis .
[86]
Thrombosis events were more commonly described in patients with Mosaic (Medtronic) and Hancock II
(Medtronic) compared with other prostheses (20.3% vs. 7.2%) in patients without anticoagulant therapy .
[83]
[87]
Among the hypotheses evaluated, it appears that this complication may result from design factors .
Therefore, a more aggressive anticoagulation regimen after ViV TAVR is recommended, especially in
patient with high thrombotic risk and low hemorrhagic risk .
[7]

Nowadays, there are no robust randomized data on antiplatelet versus anticoagulation after ViV TAVR.
Based on recent studies and randomized controlled trials, a viewpoint document, that provides up-to-date
therapeutic insights into the peri- and post-TAVI antithrombotic treatment but with no particular
recommendations regarding ViV TAVR, was recently released . Finally, the optimal antithrombotic
[52]
regimen after ViV TAVR procedures should be based on the patient’s specific anatomical (e.g., higher risk
of leaflet thrombosis) and clinical (e.g., atrial fibrillation) characteristics .
[12]

STROKE RISK IN VIV TAVR
Stroke is an independent risk factor for increased mortality following TAVR . Embolization is the main
[88]
etiopathogenetic mechanism in the periprocedural period, while late events may be either device related or
spontaneous. Despite the substantial decline in stroke rates after TAVR in the most recent trials, it remains
one of the most important adverse events .
[6]
Although degenerated surgical bioprostheses are often calcified and more fragile, no statistically significant
difference in stroke rates was identified between ViV TAVR and TAVR on native valve . Furthermore, as
[89]
reported in a recent meta-analysis by Macherey et al. , quantitative analysis demonstrated no statistically
[90]
significant difference in 30-day stroke rates, 30-day mortality, and 1-year mortality among ViV TAVR,
TAVR on native valve and redo SAVR .
[90]

Studies on cerebral embolic protection device (CEPD) have been conducted primarily on TAVR on native
valves and have been shown to reduce stroke rates but without reducing procedural complication rates or
length of stay. Debris material, thrombus, valve tissue, aortic wall or calcification, captured by a CEPD in
ViV TAVR, does not appear to be different from native TAVR procedures [91-93] . Therefore, CEPD use should