Standardized Definition of Structural Valve Degeneration for Surgical and Transcatheter Bioprosthetic Aortic Valves

Expanding TAVI to Low and Intermediate Risk Patients

TAVI has become the standard treatment in patients at increased surgical risk and is increasingly being performed in patients at intermediate to low surgical risk. While non-inferiority has been demonstrated in intermediate risk patients, several challenges—particularly with regard to valve durability—need to be addressed before expansion to lower risk and younger patients can be recommended on a broad basis. Current trends, trials results, and remaining challenges are summarized and discussed in the light of updated treatment guidelines.

Haemodynamic outcomes following aortic valve-in-valve procedure

Background and objectives

Transcatheter aortic valve-in-valve implantation (ViV) has emerged as a valuable technique to treat failed surgical bioprostheses (BPs) in patients with high risk for redo surgical aortic valve replacement (SAVR). Small BP size (≤21 mm), stenotic pattern of degeneration and pre-existing prosthesis–patient mismatch (PPM) have been associated with worse clinical outcomes after ViV. However, no study has evaluated the actual haemodynamic benefit associated with ViV. This study aims to compare haemodynamic status observed at post-ViV, pre-ViV and early after initial SAVR and to determine the factors associated with worse haemodynamic outcomes following ViV, including the rates of high residual gradient and ‘haemodynamic futility’.

Methods

Early post-SAVR, pre-ViV and post-ViV echocardiographic data of 79 consecutive patients who underwent aortic ViV at our institution were retrospectively analysed. The primary study endpoint was suboptimal valve haemodynamics (SVH) following ViV defined by the Valve Academic Research Consortium 2 as the presence of high residual aortic mean gradient (≥20 mm Hg) and/or at least moderate aortic regurgitation (AR). Haemodynamic futility of ViV was defined as <10 mm Hg decrease in mean aortic gradient and no improvement in AR compared with pre-ViV.

Results

SVH was found in 61% of patients (57% high residual gradient, 4% moderate AR) after ViV versus 24% early after SAVR. Pre-existing PPM and BP mode of failure by stenosis were independently associated with the primary endpoint (OR: 2.87; 95% CI 1.08 to 7.65; p=0.035 and OR: 3.02; 95% CI 1.08 to 8.42; p=0.035, respectively) and with the presence of high residual gradient (OR: 4.38; 95% CI 1.55 to 12.37; p=0.005 and OR: 5.37; 95% CI 1.77 to 16.30; p=0.003, respectively) following ViV. Criteria of ViV haemodynamic futility were met in 7.6% overall and more frequently in patients with pre-existing PPM and stenotic BP (18.5%) compared with other patients (2.0%). ViV restored haemodynamic function to early post-SAVR level in only 34% of patients.

Conclusion

Although ViV was associated with significant haemodynamic improvement compared with pre-ViV in >90% of patients, more than half harboured SVH outcome. Furthermore, only one-third of patients had a restoration of valve haemodynamic function to the early post-SAVR level. Pre-existing PPM and stenosis pattern of BP degeneration were the main factors associated with SVH and haemodynamic futility following ViV. These findings provide strong support for the prevention of PPM at the time of initial SAVR and careful preprocedural patient screening.

Stent and leaflet stresses in 26-mm, third-generation, balloon-expandable transcatheter aortic valve

OBJECTIVES

Transcatheter aortic valve replacement has proven successful in treating intermediate-risk, high-risk, and inoperable patients with severe aortic stenosis. Third-generation, balloon-expandable transcatheter aortic valves were developed with an outer sealing skirt to reduce paravalvular leakage. As transcatheter aortic valve replacement use expands, long-term durability questions remain. Valve design influences durability, where regions of increased leaflet stress are vulnerable to early degeneration. However, third-generation transcatheter aortic valve stresses are unknown. Our goals were to determine the stent and leaflet stresses of third-generation, balloon-expandable transcatheter aortic valves.

METHODS

The commercial 26-mm Edwards SAPIEN 3 valve (Edwards Lifesciences, Inc, Irvine, Calif) underwent high-resolution micro-computed tomography scanning to develop a precise 3-dimensional geometric mesh of the stent and valve. Leaflet material properties were obtained from surgical bioprostheses, and stent material properties were based on cobalt-chromium. Simulations of systemic pressure loading were performed, and stress was calculated using finite element analyses.

RESULTS

At diastole, maximum and minimum principal stresses on transcatheter aortic valve leaflets were 2.7 MPa and -0.47 MPa, respectively. Peak leaflet stresses were observed at upper leaflet commissures, at their connection to the stent. Maximum and minimum principal stresses for the stent were 38.2 MPa and -44.4 MPa, respectively, at 80 mm Hg and were located just below the commissural stent.

CONCLUSIONS

Stress analysis of the 26-mm SAPIEN 3 valve using exact geometry from high-resolution scans demonstrated that peak stresses for both transcatheter aortic valve stent and leaflets were present at commissural tips where leaflets were attached. These regions would be most likely to initiate degeneration. The Dacron skirt had minimal effect on stresses on leaflets and stent.

Bioprosthetic aortic valve durability in the era of transcatheter aortic valve implantation

The main limitation of bioprosthetic valves is their limited durability, which exposes the patient to the risk of aortic valve reintervention. Transcatheter aortic valve implantation (TAVI) is considered a reasonable alternative to surgical aortic valve replacement (SAVR) in patients with intermediate or high surgical risk. TAVI is now rapidly expanding towards the lower risk populations. Although the results of midterm durability of the transcatheter bioprostheses are encouraging, their long-term durability remains largely unknown. The objective of this review article is to present the definition, mechanisms, incidence, outcome and management of structural valve deterioration of aortic bioprostheses with specific emphasis on TAVI. The structural valve deterioration can be categorised into three stages: stage 1: morphological abnormalities (fibrocalcific remodelling and tear) of bioprosthesis valve leaflets without hemodynamic valve deterioration; stage 2: morphological abnormalities and moderate hemodynamic deterioration (increase in gradient and/or new onset of transvalvular regurgitation); and stage 3: morphological abnormalities and severe hemodynamic deterioration. Several specifics inherent to the TAVI including valve oversizing, manipulation, delivery, positioning and deployment may cause injuries to the valve leaflets and increase leaflet mechanical stress, which may limit the long-term durability of transcatheter bioprostheses. The selection of the type of aortic valve replacement and bioprosthesis should thus take into account the ratio between the demonstrated durability of the bioprostheses versus the life expectancy of the patient. Pending the publication of robust data on long-term durability of transcatheter bioprostheses, it appears reasonable to select SAVR with a bioprosthesis model that has well-established long-term durability in patients with low surgical risk and long life expectancy.

Expanding TAVI to Low and Intermediate Risk Patients

TAVI has become the standard treatment in patients at increased surgical risk and is increasingly being performed in patients at intermediate to low surgical risk. While non-inferiority has been demonstrated in intermediate risk patients, several challenges-particularly with regard to valve durability-need to be addressed before expansion to lower risk and younger patients can be recommended on a broad basis. Current trends, trials results, and remaining challenges are summarized and discussed in the light of updated treatment guidelines.