The main findings of this study were: (i) ViV was associated with an improvement in valve haemodynamics compared with pre-ViV in 92% of patients. (2) However, SVH—as defined by VARC2 criteria—was observed in 61% of patients post-ViV versus 24% early post-SAVR. (3) ViV was able to restore valve function to that observed post-SAVR in only 34% of patients. (4) Pre-existing PPM of the surgical BP and BP mode of failure by stenosis were the main factors associated with higher rates of high residual gradient and SVH following ViV and of haemodynamic futility of this procedure.
Haemodynamic outcomes of ViV versus initial SAVR
About one quarter of patients had SVH (exclusively high residual gradient) early after initial SAVR. This is most likely related to the presence of severe PPM. However, following ViV, this rate of SVH increased by 2.5 folds compared with post-SAVR, and only one-third of the patients had a restoration of their valve haemodynamic function to the post-SAVR level following ViV (figures 2 and 3). These findings may be explained by the fact that the ViV procedure (ie, implanting a second valve within a pre-existing one) generally reduces the internal orifice area available for blood flow, unless the BP is expanded or fractured during the procedure. An analogy to this concept would be the Russian dolls, where the second doll is necessarily smaller than the first one. Hence, although the valve haemodynamic status of the failed BP is significantly improved (ie, gradient and/or AR are reduced compared with pre-ViV) in the vast majority of patients, the ViV procedure is generally not able to restore the baseline valve function post-SAVR.
The only factor associated with restoration of valve function to that observed early post-SAVR was the presence of stented porcine BP. In stented porcine BPs, the leaflets are mounted within the stent, whereas in most stented pericardial BPs (eg, Mitroflow) included in this study, the leaflets were mounted outside the stent. Hence, in pericardial BPs, ViV generally leads to a worsening of valve haemodynamics, whereas in stented porcine BPs, the radial forces exerted by the THV during ViV may compress the BP leaflet tissue and sutures and therefore expand the internal geometric orifice area of the BP. These factors may have resulted in less decrease, or even some increase, in the internal geometric orifice area and EOA of stented porcine BPs compared with stented pericardial BPs. These findings are consistent with recent in vitro studies that reported no increase in gradients after ViV implantation of the SAPIEN12 and the CoreValve13 within normally functioning porcine BPs.
Factors associated with ViV haemodynamic outcomes
Several studies reported that severe pre-existing PPM of the BP is associated with worse functional capacity, increased risk of mortality and increased rates of high residual gradient after ViV.6 7 However, the vast majority of previous studies have focused on the post-ViV haemodynamic status and did not compare with the pre-ViV and post-SAVR status. Furthermore, significant haemodynamic and clinical benefit may occur following ViV despite the presence of high residual gradients after the procedure. For example, a reduction in pre-ViV mean gradient of 60 mm Hg to post-ViV of 25 mm Hg will likely significantly improve the functional status of the patient.
The concept of treatment futility has been applied in the context of transcatheter valve therapy to functional and clinical outcomes, but the same principles may also be applied to haemodynamic outcomes.14–16 We thus defined haemodynamic futility as the absence of significant improvement in transprosthetic gradient (<10 mm Hg) and AR (<1 grade). In the present study, ViV was haemodynamically futile in 7.6% of the patients.
Pre-existing PPM of the surgical BP was associated with increased risk of high residual gradients after ViV and haemodynamic futility of ViV. Indeed, in a patient with severe pre-existing PPM, the EOAi is already small at the time of SAVR and a ViV generally further reduces the EOAi and worsens the haemodynamic status (ie, fitting a second doll in an already small doll). Patients with no-pre-existing PPM nonetheless harboured less improvement in EOA and gradients compared with those with pre-existing PPM (online supplementary table 3, online supplementary figure 3). Patients with no pre-existing PPM also often are those in whom regurgitation or mixed dysfunction is the predominant mechanism of BP failure. In such patients, the valve haemodynamic improvement following ViV is essentially related to the reduction in transprosthetic regurgitation, and there is thus no or minimal decrease in gradients per se.
Overall, these findings further emphasise the paramount importance of: (1) avoiding PPM, especially severe PPM, at the time of initial SAVR and (2) performing systematic screening for the presence of pre-existing PPM and/or acquired BP stenosis at the time of pre-ViV assessment. The new BP generations implanted in a supra-annular position allow to surgeon to achieve the prevention of severe PPM in most patients. Another option would be to perform a transcatheter aortic valve replacement in place of SAVR. Indeed, PPM is less frequent with transcatheter aortic valve replacement than with SAVR, and ViV within a THV is associated with better haemodynamics results than within a surgical BP.17
BP mode of failure by stenosis is also associated with higher risk of high residual gradients and haemodynamic futility following ViV. This may be explained by the fact that the thickened and calcified leaflets of the failed surgical BP may limit the expansion of the THV within the BP during ViV.
Hence, the haemodynamic utility versus futility ratio of the ViV procedure should be carefully evaluated in patients with severe pre-existing PPM and/or BP stenosis. In patients with severe PPM, one may consider fracturing the BP stent with a non-compliant balloon.18 19 Further studies are however needed to assess the risk–benefit ratio and long-term outcomes of this procedure. The findings of this study also provide support to the development of new generations of surgical BPs with expansible stents to allow the implantation of a larger THV at the time of ViV.
Several studies reported that THV with supra-annular design are associated with lower rates of high residual gradient after VIV compared with THV with intra-annular design, especially in patients with small BPs and/or BPs with severe PPM.4 7 20 In the present study, the THV design was not found to be associated with worse haemodynamic outcomes after ViV. Intra-annular THVs were used in the vast majority of the patients included in this series, and the supra-annular THVs were used specifically in small BPs.