MitraClip and right ventricular function: hopes and doubts

The MitraClip® system represents an important therapeutic option in symptomatic patients with severe functional mitral regurgitation (MR) who are considered at high surgical risk. The implantation of a MitraClip® is a fairly safe procedure that is usually well tolerated, even by patients with severe left ventricular (LV) dysfunction and major comorbidities.1,2 Compared with surgical mitral valve repair, the MitraClip® is less effective in eliminating MR and is associated with a higher rate of residual or recurrent insufficiency.1,3 Nevertheless, in most of the patients, it does reduce the severity of MR, decreases LV dimensions, improves cardiac output, and leads to significant clinical benefits.1–3 The study by Giannini et al.,4 although enrolling a small number of patients, confirms most of the results reported so far. The procedure was feasible with low mortality and morbidity despite the poor pre-operative conditions of the patients. The degree of MR at discharge and 6 months was significantly lower compared with the pre-operative values, although, as reported in other series, it was not completely abolished. Indeed, residual MR ≥2+/4+ was present in 80% of the cases at hospital discharge and in 71.5% at 6 months. Actually most of those patients had moderate (2+/4+) residual regurgitation. Although valve competence was not perfectly restored, it significantly improved compared with baseline leading to a relevant clinical benefit (lower New York Heart Association functional class, decreased brian natriuretic peptide levels, and reduced Minnesota living with heart failure score). Echocardiographic assessment documented reverse LV remodelling with reduction of diameters and volumes and an increase of the ejection fraction. On the other hand, the improvement, at hospital discharge, of stroke volume and cardiac index was rather modest, although statistically significant, and did not show further increase at 6 months. This finding might be explained by the persistence, in the majority of patients, of moderate MR and with the fact that the benefit associated with the reduction of the ‘volume overload’ induced by the MitraClip is partially nullified by the higher ‘afterload’ caused by the improved valve competence. All those findings are certainly interesting, but do not add very much to our current knowledge about the MitraClip having been already reported by many other groups.1–3,5 The real original contribution provided by the authors to this topic is represented by the echocardiographic data, showing a significant improvement of the right ventricular (RV) performance after the procedure and, in particular, of its longitudinal systolic function. In concomitance with a marked reduction in the systolic pulmonary artery pressure, in fact, the tricuspid annulus plane systolic excursion (TAPSE) increased of 19% and the tissue Doppler imaging systolic velocity at the tricuspid annulus (TDI RV-Sm) improved of 39%. Both parameters significantly increased at hospital discharge compared with baseline without further changes at 6 months. The positive effect on RV function, therefore, seems to be linked mainly to the acute reduction of MR and pulmonary hypertension, rather than being the consequence of a gradual reverse remodelling of the right ventricle. Interestingly, no concurrent reduction in the RV dimensions was observed since the basal, middle, and longitudinal diameters of the right ventricle remained substantially unchanged. The authors explain this discrepancy by the technical limitations of the two-dimensional (2D) echocardiography. Certainly, 3D echo and magnetic resonance imaging would have been able to provide more reliable data. However, the explanation given by the authors, although plausible, is not entirely convincing since, in several other series, as in those dealing with the correction of functional tricuspid regurgitation (TR),6 important signs of reverse RV remodelling could be clearly documented by 2D echocardiography alone. This issue is extremely important and should be clarified by further studies since an improvement of the indices of RV function in the absence of reverse remodelling of the right ventricle might not lead to any meaningful prognostic benefit. Certainly, the increase of TAPSE and TDI RV-Sm in this study was surprisingly early, and this finding is hardly shown in patients undergoing surgical repair of functional MR where the right ventricle is adversely affected by the cardioplegic arrest. Whether such an early functional improvement is intended to be long-lasting is unknown. Doubts in this regard stem from the following observations: A careful monitoring of the right ventricle in those patients will be crucial to understand whether the benefits observed immediately after the procedure are going to be durable or not. in patients with idiopathic or post-ischaemic dilate cardiomyopathy (DCM), RV remodelling, and dysfunction are undoubtedly the consequence of the pressure overload secondary to left atrial and pulmonary hypertension, but, for the most part, they represent the ‘epiphenomenon’ of the intrinsic disease of the myocardium. The latter, of course, cannot be cured by the improvement of MR provided by the MitraClip implantation and is intended to progress; the majority of patients was left with a moderate degree of residual MR. The recently published results at 4 years of the randomized EVEREST study1 demonstrate the substantial stability of this residual MR. However, the effects of this persistent mitral insufficiency on RV size and function in DCM patients have not been clarified. If durability will eventually be proved, new therapeutic options and possibilities could be offered to patients who are now considered suboptimal surgical candidates because of RV dilatation/dysfunction. It has recently been demonstrated that a TAPSE of <15 mm at baseline is a negative predictor of combined events after the MitraClip implantation.7 A longer follow-up of the patients included in this and other similar series might help to define whether this or other cut-off values should be used to consider the candidacy of a patient to a percutaneous mitral repair procedure. Secondary TR is often present in patients with idiopathic or ischaemic DCM. It seems very likely that some of the patients included in this study had at least mild-to-moderate functional TR. It has been demonstrated that, in this context, even less than severe TR may progress despite the successful correction of MR. In our experience,8 ∼20% of the patients submitted to mitral repair for functional MR showed, about 2 years after surgery, an increase of at least two grades of their pre-operative TR, which had been left untreated because considered not clinically relevant. Unfortunately, no data are provided in this study regarding this important issue. Finally, it should be emphasized that patients with secondary MR treated with the implantation of a MitraClip are regularly followed, after the procedure, with clinical and echocardiographic examinations and receive a progressive optimization of their medical therapy. Before the percutaneous treatment, on the other hand, it is not uncommon to encounter patients whose drug therapy has been poorly adjusted during rather sporadic outpatient visits. The question, then, is whether, in this series, the post-implantation pharmacological treatment significantly changed compared with the pre-operative regimen, and whether those modifications had an impact on patients'clinical conditions. It is not unlikely that at least part of the improvements documented at 6 months might be referred to the post-operative optimization of the medical therapy. This aspect does not seem to have been adequately addressed in this and in other similar studies whereas, undoubtedly, it would deserve greater attention and investigation. Conflict of interest: none declared.