Percutaneous Valve Repair of Functional Mitral Regurgitation: Aiming at Optimal and Durable Results

This article refers to ‘The impact of residual mitral regurgitation after MitraClip therapy in functional mitral regurgitation’ by D. Reichart et al., published in this issue on pages 1840–1848. Functional, or secondary, mitral regurgitation (FMR) is associated with poor prognosis in patients with heart failure (HF). Its effect on clinical outcome depends on its severity with a linear relationship between FMR degree and long-term mortality, regardless of cardiac dysfunction and HF severity.1 Basically, mild (1+), moderate (2+) and moderate-to-severe or severe (3+ or 4+) FMR have a different, increasing, and independent prognostic impact on HF clinical history.1, 2 In this issue of the Journal, Reichart et al.3 report 5-year clinical outcomes of patients undergoing percutaneous edge-to-edge mitral valve repair for FMR at their high-volume centre. They retrospectively observed an increased rate of events, including deaths and HF hospitalizations, in patients with residual mitral regurgitation (MR) ≥ 2+ at discharge. In particular, the risk of all-cause death was about 50% higher in patients with post-procedural MR ≥ 2+ and more than twofold higher in those with MR ≥ 3+, compared with patients with residual MR ≤ 1+. In addition, also patients with recurrent MR ≥ 2+ at 1 year had a poor outcome, similar to that of patients with MR ≥ 2+ at discharge and worse than that of patients with persistent MR ≤ 1+ at 1-year follow-up.3 This study has some limitations. Its sample size is relatively small and, being a retrospective analysis, a comprehensive collection of echocardiographic data is lacking. Only 212 out of 458 patients had an available echocardiogram at both baseline and 1 year. More importantly, the lack of a blinded and independent evaluation of echocardiographic variables, including MR severity, and the lack of information about variables that may influence MR degree (i.e. medical therapy) make the results more hypothesis generating than conclusive. However, despite these limitations, the authors are to be congratulated for dealing with paramount and poorly investigated aspects of percutaneous treatment of FMR. Device success for transcatheter mitral valve interventions was initially defined as residual post-procedural MR ≤ 2+ and many observational studies showed a significant impact of post-procedural MR ≤ 2+ on early and long-term outcomes.4, 5 Currently, the Mitral Valve Academic Research Consortium classifies device success after transcatheter mitral valve interventions as ‘optimal’ or ‘acceptable’.6 ‘Optimal’ device success is defined as a reduction in MR to ≤1+, while ‘acceptable’ device success is defined as a reduction of MR by at least one degree from baseline and to an absolute level ≤2+. This classification is based on the possible different impact on outcomes of post-procedural ‘optimal’ vs. ‘acceptable’ MR. Previous data suggested haemodynamic and prognostic improvement following MitraClip also in patients with MR reduction to 2+.7, 8 However, other studies,9, 10 including that by Reichart et al.,3 showed a worse prognosis in patients with MR 2+ compared to those with MR ≤ 1+. These results are in line with previous investigations in HF patients showing a continuous relationship between the degree of FMR and mortality, consistently with the role of the regurgitant volume as a cause of left heart volume overload leading to progressive dilatation and dysfunction. Conversely, a relation between left ventricular reverse remodelling and better outcomes has been reported after both surgical and percutaneous correction of FMR.11, 12 Thus, persistence of MR, even if moderate (i.e. 2+), may promote a vicious circle leading to left heart chamber enlargement and worsening of MR itself. Accordingly, post-procedural MR 2+ was associated with a fivefold increased risk of MR ≥ 3+ at 5 years,13 and recurrence of MR (to ≥3+) within 2 years after MitraClip was a strong independent predictor of 5-year mortality and HF hospitalization.14 A second, even more interesting and novel, aspect of the analysis by Reichart et al. regards the role of recurrent FMR. Patients with MR ≤ 1+ at discharge who developed worsening MR to ≥2+ at 1-year had a long-term prognosis similar to those with MR ≥ 2+ immediately after the procedure.3 European registries showed that half of the patients receiving MitraClip had a ‘sub-optimal’ (e.g. ≥2+) result at 1-year follow-up.11, 15-17 Durability of percutaneous edge-to-edge procedures is a worrisome and poorly considered issue. Durable results in FMR patients are challenging to be obtained also by surgery. Isolated restrictive annuloplasty is associated with MR recurrence in up to 25% of patients at 6 months.18 However, combination of surgical edge-to-edge technique and annuloplasty may guarantee more durable results compared to surgical ringless edge-to-edge repair19 and also compared to percutaneous edge-to-edge repair alone.20 It should be considered that different mechanisms leading to FMR (i.e. annulus dilatation, and symmetric or asymmetric leaflet tethering) can coexist and be more or less pronounced in the same patient. In this context, an isolated edge-to-edge approach may be limiting, whereas the complementary use of different repair tools targeting specific FMR mechanisms (i.e. annuloplasty alone for symmetric tethering or annulus dilatation due to left atrial enlargement; edge-to-edge procedure alone for asymmetric tethering; annuloplasty and edge-to-edge for moderately advanced FMR with combined mechanisms) may allow improvement in the effectiveness and durability of the procedure. By now, percutaneous techniques for mitral valve repair, alternative to edge-to-edge, are also available. However, additional engineering efforts are needed for making some of these devices smoother and procedures more streamlined. Thus, optimal treatment of FMR should be tailored to individual patient's characteristics. Acute success and long-term durability of percutaneous procedures depend on careful patient management, both before, during and after the intervention (Figure 1) and this involves different specialists (i.e. HF specialists, imaging specialists, cardiac surgeons, interventional cardiologists, anaesthesiologists). In the pre-procedural phase, careful selection should be carried out to identify patients that could benefit from FMR interventions with regard to both clinical (e.g. optimized medical therapies, non-end-stage or too advanced cardiomyopathy),21 and anatomical (e.g. good probability to obtain an optimal result using available devices) aspects. At the time of the procedure, the primary aim should be to obtain optimal MR reduction (≤1+), while balancing benefits and risks, including the possibility of causing mitral stenosis or other complications, such as leaflet tear. Other aspects that should be considered include afterload mismatch, which can be successfully treated with inotropic drugs during and after the procedure, as well as loading status. In this respect, attention should be paid in evaluating residual MR degree after device deployment. General anaesthesia, and possibly pharmacological support used during the procedure, may lead to an underestimation of MR severity. Some tricks like Trendelenburg position and/or fluid loading can help for a more appropriate MR evaluation before the end of the procedure. Importantly, the final evaluation of the procedural result should not be limited to MR degree. Other echocardiographic (i.e. pulmonary venous flow, transvalvular mean gradient) and haemodynamic (i.e. mean left atrial pressure, left atrial v wave) parameters should be taken into account.22, 23 Finally, clinical and echocardiographic evaluation should be always performed during the follow-up in order to evaluate residual MR, and, especially, the need for medical therapy optimization. Increased cardiac output after FMR reduction may allow titration of evidence-based HF treatment with a further contribution to reverse remodelling. In case of MR recurrence, the possibility of performing a reintervention (percutaneously or surgically) can be considered based on clinical and anatomical features. In conclusion, being FMR a complex disease, its treatment requires management of multiple aspects. The close cooperation between different specialists is essential to properly select and monitor patients suitable for percutaneous intervention. Achieving optimal and durable FMR reduction is paramount to guaranteeing long-term benefits. Conflict of interest: none declared.

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