Advances in transcatheter technology have revolutionized the treatment of aortic valve disease, with its implantation now approved for patients of any risk category. However, the most frequent valve disease in the developed world is mitral regurgitation (MR). Clinically significant MR prevalence is approximately 2% in the general population, increasing with age, affecting more than 10% of individuals older than 75 years. This, along with rising life expectancy, results in a growing group of elderly patients and/or those with high comorbidity who may not be candidates for open surgical treatment. In fact, various publications have estimated that approximately 50% of patients with severe MR are declined for surgery due to age, comorbidities, and high surgical risk. This has led to the development of less invasive transcatheter therapeutic options to improve symptoms and quality of life for these patients.

Despite the growing evidence of feasibility and favorable outcomes with transcatheter mitral repair options (especially with edge-to-edge devices), almost 25% of treated patients exhibit moderate residual regurgitation in the short to medium term, which is associated with increased mortality. Moreover, certain valvular anatomies are not suitable for repair, such as calcified or retracted leaflets, clefts, and multiple regurgitant jets. Consequently, there has been a growing interest in developing transcatheter mitral valve prostheses (TMVR) to achieve more durable and versatile outcomes across different types of MR mechanisms. However, TMVR currently presents various technical challenges for implantation:

1. Access: The transfemoral approach, through transeptal puncture, requires large navigation systems (≥24 Fr), presenting a risk of residual interatrial shunt; these systems must also possess a high degree of flexibility to cross the interatrial septum and orient coaxially within the native mitral valve. The transapical access has shown favorable early results, but in an effort to extrapolate TAVI results, it has been suggested that it may be associated with worse outcomes than transfemoral access.
2. Device Anchoring: Unlike TAVI, where the aortic valve is often calcified and rigid, facilitating relatively easy and stable prosthetic implantation, mitral anchoring is more complex as it is performed on a generally non-calcified annulus with a three-dimensional D-shaped morphology and dynamic behavior throughout the cardiac cycle.
3. Risk of Left Ventricular Outflow Tract (LVOT) Obstruction: The degree of left ventricular dilation, septal hypertrophy, and the angle formed between the aortic and mitral annuli are important factors to consider in the planning of TMVR implantation.
4. Uncertainty Regarding Durability and Thrombogenicity.

Currently, several transcatheter mitral valve prosthesis models are designed for implantation via both transfemoral/transeptal (Evoque™ (Edwards), Sapien M3™ (Edwards), Highlife™ (Highlife), etc.) and transapical (Tendyne™ (Abbott), Intrepid™ (Medtronic), Tiara™ (NeoVasc), etc.) access. All except for the Tendyne™ prosthesis have been implanted in a limited number of patients, within clinical trials or under compassionate use, with short-term results available.

The Tendyne™ prosthesis is currently the only transcatheter mitral valve prosthesis with CE marking, with over 1,000 implants performed worldwide. It has shown favorable short- and medium-term results across various mechanisms of mitral regurgitation, even in cases of double mitral lesion and severe mitral annular calcification (MAC). This prosthesis is implanted via a transapical approach and consists of three porcine pericardial leaflets attached to two self-expanding nitinol stents, one internal, leaving a minimum effective orifice area of 3.2 cm², and an external asymmetric stent designed in the D-shape of the native mitral annulus. The device is completed with a polyethylene tether, ensuring adequate sealing and enabling prosthetic repositioning/retrieval, connected to a pad anchored at the ventricular apex, providing prosthetic stability and hemostasis. Six sizes of prostheses are available (29, 33, 35, 37, 39, and 41 mm) with standard or reduced profile. A key aspect in determining the anatomical suitability for this prosthesis implantation is preoperative assessment via TTE/TEE and cardiac CT angiography. The annular and left ventricular diameters must fall within specific ranges (especially LV end-systolic diameter >40 mm) to avoid the risk of LVOT obstruction. Using these measurements and a virtual recreation of the prosthesis implant, the neo-LVOT should be >250 mm².

Sorajja et al. published the initial outcomes in 100 patients, showing a technical success rate of 96% with no intraoperative mortality. Mortality and stroke at 30 days were 6% and 2%, respectively, with no MR in 98% of cases. The mean follow-up was 13.7 months, with a one-year survival rate of 72.4%, and 88.5% of survivors were in NYHA functional class I-II/IV.

Recent publications reported two-year outcomes, confirming the good performance of the prosthesis with more than 93% of patients without MR or evidence of prosthetic dysfunction. The survival rate was 61%, with a high functional class maintained (81.6% in class I-II/IV of NYHA).

In the subgroup of patients with severe mitral annular calcification, Gössl et al. reported outcomes in 20 patients who underwent Tendyne™ prosthesis implantation. All patients had severe MR, with 31% also presenting significant stenosis. Procedural success was 95%, with MR elimination in all cases, adequate safety (5% in-hospital mortality), and symptomatic improvement in most patients during one-year follow-up. These data represent a substantial improvement in outcomes for this high-risk surgical population compared to other published transcatheter treatments.

To provide a realistic perspective on the current status of transcatheter mitral prostheses, recent results from the CHOICE-MI (CHoice of Optimal Transcatheter Treatment for Mitral Insufficiency) multicenter registry have been published. This study involved 746 patients with severe MR, high surgical risk (mean EuroSCORE II of 6.3%), and deemed suboptimal candidates for percutaneous mitral repair, who were evaluated for transcatheter prosthesis implantation. After preoperative assessment, 229 patients met the anatomical criteria, and 10 different devices were implanted. The access route was transapical in 89.5% of cases, with a 95.2% implantation success rate. During the procedure, mortality, malposition, LVOT obstruction, and migration rates were 1.8%, 3.7%, 3.2%, and 2.3%, respectively. At one-year follow-up, residual MR >1+ occurred in 4.8% of patients, and the combined endpoint of mortality/hospitalization due to heart failure occurred in 39.2% of patients.

The role of transcatheter aortic prostheses implanted in the mitral position has also gained attention in cases of valve-in-valve (ViV) and valve-in-ring (ViR) procedures for patients with high surgical risk. The VIVID international registry, with 1,079 patients (857 ViV and 222 ViR), represents the most extensive experience to date. In most cases, the Sapien 3™ prosthesis (Edwards) was implanted, with more than 60% of cases using transapical access. Peri-procedural and 30-day mortality were 1.8% and 7%, respectively, with significant residual MR occurring more frequently in ViR than in ViV cases (16.6% vs. 3.1%, p=.001). Four-year survival was 62.5% for ViV and 49.5% for ViR (p<.001).

In patients with severe annular calcification, the MAC Global Registry reported data from 64 patients (mean STS score of 14±9.5) who underwent implantation of balloon-expandable aortic prostheses. Access routes included transapical (43.8%), transeptal (40.6%), and surgical transatrial (15.6%). Implant success was 72%, with four cases of prosthesis embolization to the left atrium and severe LVOT obstruction in 9.3% of patients. In-hospital mortality was 29.7%, and at one-month follow-up, more than 80% of patients had no residual MR and maintained a good functional class.

In summary, for patients with severe MR who are inoperable, at high surgical risk, or not candidates for percutaneous repair, transcatheter mitral prostheses have shown favorable initial clinical and hemodynamic outcomes.

The procedure’s success depends on appropriate patient selection, meticulous preoperative planning, and teamwork between cardiac surgeons, imaging specialists, and interventional cardiologists. There remain various anatomical limitations that restrict implantation indications, preventing its universalization for all potential candidates and all mitral pathologies. Although short- and medium-term outcomes are promising, further studies are required to assess the long-term safety and efficacy of these devices.

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