Transcatheter mitral valve implantation for degenerated mitral bioprostheses or failed surgical annuloplasty rings: A systematic review and meta‐analysis

Abstract Background Transcatheter mitral valve‐in‐valve (TMVIV) and valve‐in‐ring (TMVIR) implantation for degenerated mitral bioprostheses and failed annuloplasty rings have recently emerged as treatment options for patients deemed unsuitable for repeat surgery. Methods A systematic literature review was conducted to summarize the data regarding the baseline characteristics and clinical outcomes of patients undergoing TMVIV and TMVIR procedures. Results A total of 245 patients (172 patients who underwent TMVIV surgery and 73 patients who underwent TMVIR surgery) were included in the study; 93.5% of patients experienced successful TMVIV or TMVIR implantation. The mortality rates at discharge, 30 days, and 6 months were 5.7%, 8.1%, and 23.4%, respectively. The transapical (TA) access route was used in most procedures (55.2%). The TA and transseptal (TS) access routes resulted in similar outcomes. No significant differences were observed in the short‐term outcomes between the patients who developed mitral stenosis versus mitral regurgitation as the mode of failure. Conclusions TMVIV and TMVIR implantation for degenerated mitral bioprostheses and failed annuloplasty rings are safe and effective. Both procedures, via TA or TS access, can result in excellent short‐term clinical outcomes in patients with mitral stenosis or regurgitation, but long‐term follow‐up data are currently lacking to determine the durability of these procedures.

Since that time, additional patients have received TMVIV or TMVIR surgery. 5,6 This study reviews the outcomes of TMVIV implantation for degenerated mitral bioprostheses and TMVIR implantation for failed annuloplasty rings, according to the Mitral Valve Academic Research Consortium (MVARC) criteria. 7 The results are stratified according to the mitral valve failure mode and the access route. This information may aid in clinical decision making in patients with degenerated mitral bioprostheses or failed annuloplasty rings who are not candidates for repeat surgery. were used: "transcatheter mitral valve implantation" or "transcatheter mitral valve replacement" or "TMVI" or "TMVR." This analysis was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement. 8

| Study selection
The inclusion criteria were as follows: (1) patients received either a TMVIV or TMVIR implantation and (2) reported data necessary to assess the baseline characteristics and outcomes. Articles were excluded if any of the following criteria applied: (1) non-English article; (2) animal experiments; (3) no relevant information on TMVI implantation; (4) lack of details regarding postoperative outcomes; (4) TMVIV or TMVIR for native mitral valve; (5) insertion of a TMVIV or TMVIR during a full sternotomy under direct vision; and (6) meeting abstracts.

| Data extraction
The following information was extracted from each study: age, gender, logistic EuroSCORE, the Society of Thoracic Surgeons (STS) score, comorbidities, function of the other valves, history of heart surgery, New York Heart Association (NYHA) class, left ventricular ejection fraction, mitral regurgitation (MR) severity, mean transmitral gradient, prior mitral bioprostheses, death, valve migration, access site, and vascular and other postprocedure complications. For those patients who were reported in two or more articles, we removed the duplicates by checking their age, gender, logistic EuroSCORE or STS score, prior mitral bioprostheses, and the author's contact address. For the subgroup analysis, we recorded the mitral valve failure mode, access route, and size of the transcatheter valve. Two reviewers extracted the data independently using a predefined Excel form.

| Statistical analysis
Continuous variables are described as means and standard deviations for normally distributed data, or medians and interquartile ranges for non-normally distributed data. Differences between continuous variables were analyzed using a t-test. Categorical variables are described with absolute and relative frequencies. Differences between categorical variables were evaluated using the chi-square test or Fisher's exact test. Survival curves were estimated by the Kaplan-Meier method. A P-value <0.05 was considered statistically significant.  Table 1.

| Procedure
Transapical (TA) access was performed in 127 (55.2%) cases, and transseptal (TS) access (via a transfemoral or transjugular venous route) was performed in 91 (37.7%) patients. In addition to TA and TS access, a direct transatrial access using a sheath placed directly into the left atrium via a right anterior thoracotomy was also used in two patients. 67,101 The "TA + TS" access was utilized for the Melody    Table 3). The cumulative events at 30 days and 6 months postoperatively are shown in Table 4. Three and nine additional deaths  (Table 5), no significant differences were observed between the MR and MS groups, but MS patients in the TMVIR group had a higher mean transmitral gradient (P = 0.002). Different mitral failure modes (MR and MS) did not affect the patient's overall survival in both the TMVIV and TMVIR procedures (P = 0.347 and 0.958, respectively) ( Figure 2).

| Comparison of different access routes
Patients who underwent the TMVIV procedure via TA access had a higher incidence of concomitant aortic or tricuspid valve dysfunction  did not affect the patient's overall survival in both the TMVIV and TMVIR procedures (P = 0.450 and 0.361, respectively) ( Figure 3).

| Percentage of oversized valves
We collected manufacturer inner diameter (ID) measurements for MOSAIC and HANCOCK bioprostheses and the size of the ES valve (     access routes, but no significant differences were found.

| TA versus TS access
The first transcatheter mitral valve implantation in humans was performed via TS access. 3 In 2013, all TMVIV procedures were successfully performed via a TA approach. 63 The TA route was used for most procedures. The TA access has the following advantages: (1) direct and co-axial access; (2) shorter distance; and (3)       shape of the SAPIEN XT valve due to a final positioning that favored the atrial side (30% to 35% on the atrial side). 52 Unlike the TMVIV procedure, no consensus exists regarding the optimal position for the TMVIR procedure. A total of nine articles reported variable positions.
The three different positions of the ES valve are as follows: (1) less atrium more ventricle: 1/3 in the atrium and 2/3 in the ventricle 75,101,104 or 40% in the atrium and 60% in the ventricle 90  | 515 mean extent of oversizing in MR patients was greater than that in MS patients, but both mean proportions were less than 10%, with no significant difference between groups (P = 0.141). Due to a lack of data regarding migration, we could not determine whether migration occurred more frequently in patients with a larger mean extent of oversizing.

| Limitations
This is an observational study and all patients' data were obtained from published articles collected during a comprehensive and systematic search. Only a few articles reported long-term follow-up data; therefore, evaluation of long-term outcomes was not possible. All studies included in this study lacked control groups.

| CONCLUSION
Use of the TMVIV or TMVIR procedure for degenerated mitral bioprostheses or failed annuloplasty rings is a highly feasible, safe, and effective technique for the treatment of either valve stenosis or regurgitation for those patients who are not candidates for repeat surgery. Both the TMVIV and TMVIR procedures are associated with excellent short-term clinical outcomes. The technical success rate of TMVIV was significantly higher than that for TMVIR, and the MR rate of TMVIV was significantly lower than that for TMVIR. No significant differences in short-term outcomes were observed between the TA and TS access groups, especially regarding vascular complications.
Technical criteria, such as size selection and valve location, have not been established for transcatheter mitral valve implantation. Larger clinical trials are required to determine the durability and long-term outcomes of TMVIR and TMVIV.

CONFLICTS OF INTEREST
There are no conflicts of interest to declare.