Implantation of a transcatheter valve in massive mitral annular calcification (ViMAC) has emerged as an alternative to traditional surgical mitral valve (MV) replacement, as highlighted last year when we reviewed the study by Smith et al. Furthermore, this blog has thoroughly reviewed the evidence and use of transcatheter prostheses in mitral valve disease across all possible scenarios, including specific cases such as valve-in-valve/ring mitral (ViVM) in failed bioprosthetic or annuloplasty repairs. Most studies evaluating ViMAC are impractical due to grouping the transeptal, transapical, and transatrial forms of the procedure, creating uncertainty by preventing individualized analysis of the advantages and disadvantages of each technique. This study aims to evaluate clinical outcomes specifically for transatrial ViMAC using the most extensive multicenter registry to date. 

For this purpose, patients with symptomatic MV dysfunction and severe mitral annular calcification (MAC) were included in a ViMAC study conducted in 12 centers across the United States and Europe. Clinical characteristics, procedural details, and clinical outcomes were extracted from electronic medical records. The primary endpoint was all-cause mortality. We analyzed 126 patients who underwent ViMAC, with a median age of 76 years (interquartile range [IQR] 70-82 years), 28.6% of whom were female. The median score on the Society of Thoracic Surgeons (STS) risk scale was 6.8% (IQR 4.0%-11.4%), with a mean follow-up of 89 days (IQR 16-383.5 days). Of these patients, 61 (48.4%) presented isolated mitral stenosis, 25 (19.8%) had isolated mitral regurgitation (MR), and 40 (31.7%) presented mixed MV disease. Technical success was achieved in 119 (94.4%) patients. Thirty (23.8%) patients underwent concomitant septal myectomy, and 8 (6.3%) experienced left ventricular outflow tract obstruction (7 of 8 did not undergo myectomy). Five (4.2%) of the 118 patients with postprocedural echocardiographic data presented more than mild paravalvular leakage. All-cause mortality at 30 days and one year occurred in 14 (11.1%) and 33 (26.2%) patients, respectively. In multivariable models, moderate or greater MR in early postprocedural phases was associated with increased risk of one-year mortality (hazard ratio 2.31; 95% confidence interval 1.07-4.99; p = .03). 

The authors conclude that transatrial ViMAC is safe and feasible in this selected, predominantly male cohort. Moreover, they suggest that patients with significant MR may derive less benefit from ViMAC compared to those with isolated mitral stenosis. 

COMMENTARY:

The results of this study position the ViMAC alternative as a significant shift in MAC treatment, highlighting an innovative approach that promises to transform future practices in cardiovascular surgery with promising, comparable, and sometimes superior results to traditional surgical methods. 

The article reviewed today highlights the evolution and clear trend towards adopting less invasive techniques in MAC cases. Brener et al. present a study on 126 patients treated with the ViMAC technique over seven years, demonstrating significant advancement in this field. In comparison, last year, we reviewed the study by Smith et al., then the largest published, with 51 patients undergoing open surgical implantation of balloon-expandable transcatheter prostheses in MAC scenarios. That study reported 30-day and one-year mortality rates of 13.7% and 33.3%, comparable to the current study, with 30-day and one-year mortality rates of 11.1% and 26.2%, respectively. This indicates that in the two largest documented series to date, 30-day mortality slightly exceeds 10%, reaffirming the technique’s reproducibility and favorable outcomes. Other results obtained are frankly positive and comparable to those expected in conventional mitral surgery in similar high-severity and complex cases, showing a technical success rate of 95% and a paravalvular leakage rate of 4.2%. 

The study authors employ a technique similar to the one we detailed last year. This approach offers the main advantage of allowing anterior leaflet resection while minimizing posterior mitral annular manipulation. It enables sutures at various annular positions using Teflon pledgets on the atrial surface, adapting to the anatomy to secure them to the prosthetic cuff and reduce periprosthetic leaks. It also facilitates myectomy when the predicted left ventricular outflow tract area (LVOT) is less than 200 mm². In this study, myectomy was performed in 1 out of 4 patients, of whom only 3.3% experienced LVOT obstruction. Conversely, among patients who did not undergo concomitant myectomy, LVOT obstruction was observed in 7.3%. Therefore, the incidence of LVOT obstruction in this series was low, thanks to both anterior leaflet resection and myectomy, showing significant improvement in LVOT free space not observed in strictly transcatheter procedures (percutaneous transeptal or transapical). This improvement represents one of the main advantages and findings in using balloon-expandable prostheses in MAC patients. Alongside preventing atrioventricular groove rupture, by avoiding annular calcification resection, the optimization of LVOT space with these prostheses stands as one of the major benefits of this technique. 

These results underscore the efficacy of transcatheter prostheses when applied via a surgical approach, showing very good outcomes in cases where prognosis with traditional surgical techniques was unfavorable. On the other hand, the effectiveness of these same prostheses fully implanted by transcatheter routes, especially in contexts less complicated than those associated with MAC, has yet to be determined. Numerous clinical trials are currently underway to evaluate the outcomes of purely transcatheter mitral valve replacement (TMVR), employing transapical or transeptal approaches, with or without complementary techniques such as the LAMPOON (laceration of the anterior mitral leaflet) procedure and/or alcohol septal ablation. To date, no device has replicated all the advantages observed with the transatrial approach, which include complete anterior leaflet excision, myectomy when necessary, prosthesis placement and orientation under direct vision, and sutures to prevent perivalvular leaks. It is likely that with new devices, where the implant position of the balloon-expandable transcatheter prosthesis is more predictable, the commissural alignment relative to the LVOT will further improve obstruction outcomes and reduce the need for associated myectomy. 

Although this surgical technique can be considered successful, confronting MAC represents one of the greatest challenges for any surgeon, and patient prognosis, regardless of the intervention performed, seems intrinsically unfavorable in the medium term. This fact is evidenced in the mentioned study, where one-year mortality was 35.4%, comparable to the 38.5% observed in the transatrial subgroup of the MITRAL study. A recent meta-analysis comparing TMVR outcomes in MAC patients using different techniques revealed a one-year mortality rate of 16% for conventional surgery and 43% for prostheses implanted exclusively percutaneously through transapical or transeptal access. This emphasizes the gap towards achieving optimal outcomes with percutaneous techniques in treating this pathology, likely attributed more to high comorbidity and fragility in these patients than to the implant technique per se. 

This study represents a valuable addition to the existing literature but is not without significant limitations, the main one being its retrospective nature. The lack of prospective data collection is especially relevant concerning critical variables such as preoperative LVOT gradients, right-sided hemodynamic pressures, or frailty criteria, for which detailed information is unavailable. The study began in 2014, a period before the adoption of a standardized MAC definition based on CT imaging criteria, limiting comparability with subsequent research. Additionally, the criteria followed by surgeons to decide on myectomy remain unknown, introducing potential selection bias. 

The introduction of transcatheter prosthesis implantation via transatrial approach in TMVR in MAC cases has marked a revolutionary shift in managing these situations, presenting itself as an innovative treatment alternative that has surprisingly emerged to establish itself permanently. Although it remains an off-label use of this type of prosthesis, the article presenting the largest-ever published series of patients treated in this manner is evidence of this advancement, delivering results deserving recognition. The application of these prostheses could pave the way for their use in scenarios beyond MAC, such as in mitral stenosis cases accompanied by other surgeries extending the procedure duration, reoperations for dysfunctional prostheses, or in complex exposure situations, to name a few examples. Although it is currently premature to even consider these possibilities, some discoveries prompt us to explore doors yet unopened, revealing opportunities that have always been before us. 

REFERENCE:

Brener MI, Hamandi M, Hong E, Pizano A, Harloff MT, Garner EF, et al. Early outcomes following transatrial transcatheter mitral valve replacement in patients with severe mitral annular calcification. J Thorac Cardiovasc Surg. 2024 Apr;167(4):1263-1275.e3. doi: 10.1016/j.jtcvs.2022.07.038.