Mitral valve regurgitation (MR), the most common type of valvular heart disease, affects nearly 10% of people above the age of 75 years [1]. It is—aside from aortic valve stenosis—the second most frequent indication for heart valve surgery in Europe [2]. MR is classified as primary, when the underlying pathology includes a structural or degenerative abnormality of the mitral valve itself. The secondary MR is caused by left ventricular dysfunction. Secondary MR can develop due to both ischemic and nonischemic cardiomyopathies, in which the pathological processes of remodeling of the ventricle or the atrium lead to a consecutive insufficiency of the mitral valve apparatus comprising leaflets, chordae tendineae, papillary muscles, or mitral annulus. In chronic MR, there is no drug proven to improve long-term outcomes [3], whereas surgery and transcatheter mitral valve repair show positive effects [4]. The MitraClip is a polyester-covered cobalt-chromium device, which can be implanted percutaneously through the femoral vein into the left atrium following transseptal puncture [5]. The clipping procedures based on the surgical technique first described by Alfieri. This intervention receives a IIb recommendation in the recent AHA/ACC valve guideline update for patients with NYHA class III-IV symptoms in a setting of chronic severe MR despite optimal medical treatment with favorable mitral valve anatomy, a reasonable life expectancy, and a high risk for mitral valve surgery [3]. Due to reduction of the mitral valve regurgitation volume after MitraClip implantation the procedure has been associated with acute reduction in pulmonary artery pressure (PAP) evaluated by echocardiography or invasively by right heart catheterization (RHC) in previous studies [6]. Right heart catheterization is considered the gold standard, but it remains a time-intensive and invasive technique that may preclude its use as a frequent method of follow-up in patients with pulmonary hypertension. Consequently, diffusing capacity of the lung (DLCO)—a non-invasive technique of CO assessment—may be a good agreement compared to thermodilution and the Fick method in RHC examinations, which can be simply conducted in most patients [7]. Increased left atrial pressure leads to the elevation in pulmonary venous pressure, which is in turn transferred to pulmonary capillaries causing damage to the alveolar-capillary barrier [8]. We hypothesize, that this mechanism leads to the decrease of DLCO, which should improve after the reveal from the valvular disease following the clip procedure. Despite rapidly increasing numbers of interventional mitral valve repairs, these alterations are still assumptions, and up to now little is known about the effects of the treatment on pulmonary circulation and changes in lung function in these patients.

The study analyzes changes in diffusing capacity of the lung for carbon monoxide (DLCO), vital capacity (VC), total lung capacity (TLC), residual volume (RV) and forced expiratory volume in 1 s (FEV1) in patients with MR before and 6 weeks after MitraClip implantation. Furthermore, clinical and echocardiographic parameters including systolic pulmonary artery pressure (sPAP) and left ventricular ejection fraction (LVEF) were done to detect changes in hemodynamic parameters.

This observational, prospective, single-arm, single center clinical study was designed to compile real-world clinical outcome data for percutaneous edge-to-edge mitral valve repair technology utilizing the MitraClip device (Abbott, Menlo Park, CA, USA). The registry was initiated in May 2016. This study was approved by the University of Dresden (Germany) and was performed at the Cardiology Department of HELIOS Hospital Pirna.

The aim of the study was to analyze changes in lung function tests and echocardiographic parameters before and 6 weeks after MitraClip implantation in patients with MR. The MitraClip procedure could be performed successfully in all 43 patients leading to a reduction of MR in 97.7% of cases. However, one patient died on day 4 after the intervention most likely due to pulmonary artery embolism. 42 patients were analyzed before and 6 weeks after implantation. 79.1% of them showed an MR of at most mild. Furthermore, we could demonstrate a significant reduction of pulmonary artery pressure during follow-up. No changes in LVEF were detected. These data are in good accordance with data from the COAPT trial [4]. We haven´t performed six-minute walk test (6MWT) in this study because changes of 6MWT, showing an improvement of the walking distance after MitraClip have been published before [13]. Comparing pre and post implant lung function tests, no significant alterations were seen for VC, TLC, and FEV1. The values of DLCO improved in most patients and in a subgroup of patients with severe preexisting deterioration of DLCO the MitraClip procedure resulted in a significant improvement in DLCO. These findings demonstrate a reversibility of pulmonary dysfunction due to MR, as this might be attributed predominantly to interstitial and alveolar edema. The quantitative evaluation of the pulmonary diffusing capacity reflects the state of the pulmonary interstitium and the alveoli. As soon as the diffusion process in the lung is impaired, hypoxemia and dyspnea occur [9]. According to Zou et al. the value of DLCO can be used as a non-invasive screening tool for the identification of exercise PH in a referral population [12]. DLCO measures the transfer of inhaled gas to red blood cells within pulmonary capillaries and reflects the properties of the alveolar–capillary membrane. Reduced DLCO in pulmonary arterial hypertension (PAH) may be the result of vascular remodeling being associated with a proportional reduction in the diffusion capacity of the alveolar capillary membrane and the total pulmonary capillary blood volume available for gas exchange [13]. Evidence suggests, that patients with long-term mitral valve disease may also present with bronchial hyperreactivity [10]. From a pathophysiologic point of view, the reduction of sPAP could be associated with the reduction of the compression of the small airways. FEV 25–75%, which reflects changes exclusively in the small airways, should thus be considered for analysis in the future trials. The present results indicate an improvement of DLCO after MitraClip implantation in patients with MR even if the preexisting DLCO is severely deteriorated. According to Mustafa et al., deterioration in pulmonary function is correlated to severity of cardiac dysfunction and may be reversible late after valve surgery, except in very advanced cases that have poor prognosis [11]. In this study, cardio surgery patients with severe valve disease who started with low values of DLCO showed improvement in the early postoperative period. We attribute this result to the reduction in alveolar and interstitial fluid amount due to improvement of the heart failure. Thus, at least for the group of patients with moderately to severely impaired baseline diffusion capacity (DLCO ≤ 50%), our hypothesis was confirmed.

Treatment of MR with the MitraClip system successfully reduces MR severity in the vast majority of patients. Consecutively a reduction in pulmonary pressure could be observed, however no changes in LVEF were obvious. Lung function tests remained mostly unaltered during follow-up, but DLCO improved in majority of patients. Moreover, in a subgroup of patients with severe preexisting deterioration of DLCO the MitraClip procedure resulted in a significant improvement in DLCO. Larger prospective trials are needed to confirm whether these effects translate into clinical outcomes.