Structural valve deterioration (SVD) refers to intrinsic alterations of bioprosthetic heart valves such as leaflet fibrosis and/or calcification, leaflet tear, and pannus that eventually lead to their hemodynamic dysfunction. Bioprosthetic failure (BVF) defines any clinically expressive valve dysfunction related to SVD or other conditions, such as endocarditis and prosthetic valve thrombosis, that eventually requires valve reoperation or reintervention (1). The clinical manifestation of bioprosthetic failure varies according to the severity of valve dysfunction. Literature is scarce on specific mechanisms and clinical presentation of SVD after TAVR, notably on self-expanding valve ACURATE Neo (Boston Scientific, Ecublens, Switzerland). We herein report on two cases with distinct mechanisms of SVD after ACURATE Neo implantation leading to BVF.

Data on specific mechanisms of SVD affecting TAVR prostheses, their incidence, and clinical presentation are limited.

The PARTNER-1 (Placement of Aortic Transcatheter Valves) trial (n = 1057) and CoreValve High-Risk Pivotal trial (n = 795) reported extremely low rates of severe SVD with 0% and 0.8% after 5 years for SAPIEN (Edwards Lifesciences, Irvine, CA, USA) and CoreValve (Medtronic, Minneapolis, MN, USA), respectively (2, 3). However, interpretation of these findings is limited due to the small number of survivors at 5 years, as predictable with typically elderly and frail patients included in these historical cohorts. With the introduction of standardized criteria for SVD, longer follow-up, and inclusion of younger, lower-risk patients in prospective TAVR trials in recent years, higher rates of SVD were reported. The NOTION (Nordic Aortic Valve Intervention) trial (n = 139), referring to the European Association of Percutaneous Cardiovascular Interventions (EAPCI), reported SVD risk after CoreValve implantation as high as 4.8% at 6 years (4). Analyzing data from the PARTNER-2A trial (n = 1438) and PARTNER-2/SAPIEN-3 Intermediate-Risk registry (n = 891) and referring to the Valve Academic Research Consortium 3 definitions, Pibarot et al. reported SVD risks of 3.9% and 9.5% at 5 years after implantation of Edwards SAPIEN 3 and Edwards SAPIEN XT, respectively (5). However, the rates of BVF were rather low (1.1% and 3.7% for Edwards SAPIEN 3 and Edwards SAPIEN XT, respectively). Also, large European retrospective cohort studies on multiple TAVR devices reported 5-year rates of SVD ranging from 2.5% to 4.2% and low rates of SVD-related BVF according to the EAPCI guidelines (6, 7). The heterogeneity of the above-mentioned rates of SVD makes their interpretation difficult and can be explained by at least two factors: first, the underestimation of the incidence of SVD given the substantial competitive risk of death in cohorts with a high mortality on short term (e.g., PARTNER-1), and second, the variability of SVD criteria according to the definitions used. An overview of SVD rates reported by the major historical randomized control trials and retrospective cohort studies focusing on TAVR durability is given in Table 1.

When looking at surgical registries of SAVR after TAVR (n = 123 and n = 46), SVD accounted for 10%–15% of indications for TAVR explant in two recent retrospective studies (8, 9).

Since ACURATE Neo is a more recent and less implanted model of the TAVR era, less information is available about long-term outcomes and specific failure mechanisms of this device.

In the SCOPE-2 (Safety and Efficacy Comparison of Two TAVR Systems in a Prospective Randomized Evaluation 2) trial (n = 796), ACURATE Neo was challenged with its self-expandable concurrent Medtronic CoreValve Evolut (10). The authors observed more frequent cardiac deaths at 1 year (8.4% vs. 3.9%; p = 0.01), more frequent severe aortic regurgitation in the short term (10% vs. 3%, p = 0.002), and more frequent structural valve deterioration in the short term (14% vs. 6%, p = 0.004) with ACURATE Neo. However, structural valve deterioration was no more statistically different after 1 year (10% vs. 14%, p = 0.25) and the valve-related dysfunction requiring repeat procedure was similarly low in both devices (1%, p = 0.99). Reporting on mid- and long-term results after ACURATE Neo implantation (n = 104), Siquiera et al. mentioned a single case of SVD-related failure addressed with a valve-in-valve procedure (11). The authors concluded with overall reassuring mid- to long-term outcomes with this device. Findings of the SCOPE-2 trial at 1 year and those of Siquiera et al. are summarized in Table 1. In our institution, we observed a rate of SVD-related BVF of 0.84%, accounting for the two present cases over the past 5 years, which was similar to the previously mentioned studies. Finally, reviewing the international EXPLANT-TAVR registry (n = 269), Bapat et al. noticed six surgical explants of ACURATE Neo (4.5% of all self-/mechanically expandable devices), but neither the causes for explant nor the durability of the failed prostheses was specified (12).

As the number of TAVR in even younger patients increases, the need to manage late complications with TAVR will increase. The number of former implanted and available TAVR models is also increasing. As such, a better understanding of the specific mechanisms of SVD affecting TAVR prostheses is mandatory. Our two cases contribute to increasing knowledge in this area by illustrating two close but specific modes of SVD leading to acute bioprosthetic failure of the ACURATE Neo. A macroscopic examination of the valves revealed no signs of active endocarditis, and the blood cultures were negative. Eubacterial PCR from leaflet samples was not performed to exclude previous endocarditis. Leaflet tear/disruption is a rare yet well-documented mechanism of SVD of surgical bioprostheses, especially those with externally mounted leaflets (13–16). Leaflet disruption in aortic bioprosthesis occurs abruptly, and the affected patient typically presents with acute, clinically poorly tolerated aortic regurgitation, as in the two present cases. In the absence of endocarditis criteria, we assumed that the rupture of the leaflet was due to mechanical fatigue by an analogous mechanism to that affecting surgical bioprostheses. To the best of our knowledge, this issue with ACURATE Neo has never been reported.

As for therapy, we opted for TAVR explant and SAVR. Our strategy was driven in both cases by the limited experience reported with valve-in-valve procedures in failed ACURATE Neo, in the second case by the rather shallow aortic root with subsequent risk of coronary obstruction. Indeed, recent works highlighted the increased risk of coronary obstruction following redo-TAVR with high-profile index bioprosthetic valves such as ACURATE Neo (17). Further studies are warranted to define the best approach to failed TAVR prostheses with respect to the index model, mode of failure, and patient´s anatomy.