Transcatheter aortic valve implantation (TAVI) has redefined the invasive treatment of severe aortic stenosis over recent decades, progressively expanding from elderly patients at high surgical risk to lower-risk profiles. The valve-in-valve strategy, namely TAVI within a previous degenerated bioprosthesis, has also become established as an effective alternative to redo surgery in patients with significant operative risk.
By contrast, dysfunctional mechanical valves have so far remained beyond the scope of structural intervention, mainly because of the assumed technical limitations arising from their design, which pose a challenge for a percutaneous approach. As a result, patients with dysfunctional mechanical prostheses and prohibitive surgical risk have no therapeutic option beyond medical treatment.
This study challenges that premise and puts forward 2 hypotheses: whether a transcatheter aortic bioprosthesis can be implanted within dysfunctional mechanical valves in inoperable patients; and whether anticoagulation could be replaced by single antiplatelet therapy when there is no other indication apart from the mechanical prosthesis.
The technique consists of disrupting a bileaflet mechanical prosthesis by balloon inflation, with the aim of freeing the prosthetic ring so that it can be used as the anchoring structure for implantation of a transcatheter bioprosthesis (Myval™ or Evolut™). One of the challenges is retrieval or isolation of the metallic discs, for which intra-aortic filters are used to prevent embolism, or alternatively the fragments are isolated by overlapping the bioprosthesis.
Bench testing was initially performed to define a technically feasible strategy. Subsequently, mechanical prostheses were implanted in 20 animal models (pigs), 11 in the heterotopic position and 9 in the orthotopic position. In the heterotopic model, procedural success was 87.5% among those surviving the first surgical phase, with consistent retrieval of fragments. In the orthotopic model, the 2 animals that reached the TAVI phase died shortly thereafter: autopsy showed thrombosis, probably related to TAVI underexpansion in small prosthetic rings (16 mm).
The strategy was then translated to humans. Three patients deemed inoperable underwent compassionate-use treatment: one man with embolization of 1 disc during a previous endovascular procedure, another with an immobile disc causing heart failure, and one woman with 3 previous cardiac operations and a 21-mm prosthesis. TAVI implantation was successful in all 3 patients. In 2 of them, anticoagulation was replaced by single antiplatelet therapy. At 6 months, all patients were alive, with normally functioning valves, no leaflet thrombosis on follow-up CT, and no ischaemic or bleeding events.
COMMENTARY:
This study undoubtedly represents a clearly disruptive proposal, as it challenges one of the current limits of structural intervention and raises the possibility of percutaneous valve replacement within a mechanical prosthesis. Beyond its technical interest, its main contribution is that it opens the door to offering a therapeutic alternative to a group of patients who, until now, appeared to be confined to palliative pharmacological strategies without viable interventional options.
The study fulfils its fundamental objective by demonstrating the premise that the procedure is, at least from a technical standpoint, feasible.
However, the experimental nature of the study prevents any conclusions from being drawn regarding clinical outcomes. The human experience is limited to 3 cases, with only 6 months of follow-up, and therefore no robust data can be obtained in terms of safety, efficacy, or reproducibility. Even so, the fact that all 3 patients survived this period without relevant adverse events is an encouraging finding, supporting the plausibility of the technique in highly selected scenarios.
Once this first conceptual barrier has been overcome, a foundation is established on which several challenges that will determine its real-world applicability can begin to be addressed. Among these, reproducibility is a key issue. The reported cases involved patients with specific characteristics and prosthetic models, treated at a high-volume centre with extensive experience in structural intervention. Validation of this strategy will necessarily require larger studies and, given its limited prevalence, multicentre data to assess its applicability across different clinical settings. This will also require a coordinated effort in training and team standardization.
As with any emerging technique, numerous questions will arise regarding protocolization. These include the differential behaviour of various types of prostheses, the absence of devices specifically designed for this type of procedure, and the need to consider alternatives to femoral access in complex situations.
If the concept were to become established, it will be essential to determine its true clinical benefit. This would require demonstration that the procedure is safe, provides adequate haemodynamic results, and has acceptable durability. More importantly, in operable patients, it would need to show outcomes superior to those of the already established technical alternative: surgical redo valve replacement. In this regard, the study itself highlights the importance of achieving optimal prosthetic expansion, since failure to do so is associated with serious complications such as thrombosis, as shown in the animal models. For these issues, surgical technique allows the addition of aortic root/annular enlargement procedures (Nicks, Manouguian, Núñez, Bo Yang), which can provide a proven effective solution without adding excessive complexity or morbidity to the procedure. Likewise, embolic risk is inherent to the technique because of disc disruption, justifying the use of specific protection systems and requiring a more detailed assessment of its clinical impact. By contrast, control of potentially embolizable material is far greater with surgery, both for native prostheses and in redo procedures.
A particularly interesting aspect of this strategy is antithrombotic management. The possibility of transitioning from anticoagulation to antiplatelet therapy raises questions of major clinical relevance that will also need to be evaluated. However, persistence of the mechanical frame at the base of the TAVI neosinuses could add further thrombotic complications to those already known for this type of implant, particularly if oral anticoagulation is discontinued. In the setting of redo valve replacement, the possibility of replacing the mechanical prosthesis with a bioprosthesis is especially attractive, with consideration of the aforementioned aortic root/annular enlargement techniques or the use of sutureless prostheses (Perceval®) to avoid significant prosthesis–patient mismatch.
Ultimately, this strategy redefines the current boundaries of interventional treatment in patients with valvular heart disease and emerges as a potential hope for a clinical context with no alternatives in very selected cases.
REFERENCE:
Amat-Santos IJ, Real C, Galán-Arriola C, Diz-Díaz J, Párraga R, Pérez-Camargo D et al. Transcatheter aortic valve-in-mechanical valve replacement: a first-in-human study. Eur Heart J. 2026 Jan 30;ehag019. doi: 10.1093/eurheartj/ehag019.
