Transcatheter Mitral Valve Repair Therapies: Evolution, Status and Challenges

Transcatheter Treatment Options for Functional Mitral Regurgitation: Which Device for Which Patients?

Mitral regurgitation is the most common valvular disease in the developed world, with approximately 24.2 million people being affected worldwide and a higher prevalence in older age groups. Surgical correction of degenerative mitral regurgitation is the standard of care and can restore cardiac function and provide a lasting result, especially when the mitral valve can be repaired. Secondary mitral regurgitation, or functional mitral regurgitation (FMR), describes atrial or ventricular factors leading to poor coaptation of an otherwise non-diseased valve. For FMR, traditional surgery has not produced the same level of benefit. Transcatheter mitral repair and replacement techniques that mimic surgical correction are under investigation. Transcatheter edge-to-edge repair is the only approved catheter-based therapy for FMR in the US. Here, the transcatheter treatment options for FMR are reviewed.

Image-Guided Targeted Mitral Valve Tethering with Chordal Encircling Snares as a Preclinical Model of Secondary Mitral Regurgitation

Development of transcatheter mitral valve interventions has ushered a significant need for large animal models of secondary mitral regurgitation. Though currently used heart failure models that chronically develop secondary mitral regurgitation are viable, the severity is lower than patients, the incubation time is long, and mortality is high. We sought to develop a swine model of acute secondary mitral regurgitation that uses image-guided placement of snares around the mitral chordae. Twenty-seven adult swine (n = 27) were assigned to secondary mitral regurgitation induced by valve tethering with image-guided chordal encircling snares (group 1, n = 7, tether MR (tMR)); secondary mitral regurgitation by percutaneous posterolateral myocardial infarction causing ventricular dysfunction and regurgitation (group 2, n = 6, functional MR (fMR)); and control animals (group 3, n = 14). Regurgitant fraction in tMR was 42.1 ± 14.2%, in fMR was 22 ± 9.6%, and in controls was 5.3 ± 3.8%. Mitral tenting height was 9.6 ± 1.3 mm in tMR, 10.1 ± 1.5 mm in fMR, and 5.8 ± 1.2 mm in controls. Chordal encircling tethers reproducibly induce clinically relevant levels of secondary mitral regurgitation, providing a new animal model for use in translational research.

Left Ventricular Thinning and Distension in Pig Hearts as a Reproducible Ex Vivo Model of Functional Mitral Regurgitation

Functional mitral regurgitation in the setting of an enlarged heart is challenging to repair surgically with an annular approach, and the need to develop subannular and ventricular approaches is recognized yet unrealized because of the lack of models for investigations. In this study, we report a novel model of functional mitral regurgitation induced by left ventricular thinning and distension in pig hearts. Seven pig hearts were explanted at a local slaughterhouse, and left ventricular distension induced by thinning the ventricular myocardium by 60-65% of its original thickness. Distension of the thinned hearts with a 120 mmHg column confirmed significant left ventricular dilatation and mitral valve tethering. These hearts were then mounted into a pulsatile flow model and animated at 120 mmHg left ventricular pressure, 5 L/min cardiac output at 70 beats/min. Echocardiography was used to assess valvular kinematics and hemodynamics. Left ventricular wall thickness reduced by 60.5% ± 10.1% at the basal plane, 64.8% ± 11.3% at the equatorial plane, and 64.0% ± 11.4% at the apical plane after thinning. Upon distension, ventricular volumes increased by 852.4% ± 639.8% after left ventricular thinning, with an 89.5% ± 33.9% increase in sphericity index. Mitral valve systolic tenting height increased from 7.92 ± 2.06 to 15.02 ± 3.89 mm, systolic tethering area increased from 130.7 ± 38.2 to 409.9 ± 124.6 mm and an average mitral regurgitation fraction of 24.4% ± 16.6% was measured. In a case study, use of multimodality imaging to test the efficacy of transcatheter mitral devices was confirmed. Ventricular wall thinning leading to passive left ventricular distension and dilatation is a reproducible ex vivo model of mitral valve tethering and functional mitral regurgitation, which in combination with multimodality imaging provides a good simulation model.

Computer simulations of transapical mitral valve repair with neochordae implantation: Clinical implications

OBJECTIVES

Transapical beating heart neochordae implantation is an innovative mitral valve repair technique that has demonstrated promising clinical results in patients with primary mitral regurgitation. However, as clinical experience continues to increase, neochordae implantation criteria have not been fully standardized. The aim of this study was to investigate the biomechanical effects of selecting an antero-lateral apical access site compared with a postero-lateral site, and suboptimal neochordae length compared with optimal suture length, on restoring physiologic left heart dynamics.

METHODS

Transapical neochordae implantation using 3 and 4 sutures was computer simulated under 3 posterior mitral leaflet prolapse conditions: isolated P2, multiscallop P2/P3 and multiscallop P2/P1. Physiologic, pre- and postrepair left heart dynamics were evaluated using a fluid-structure interaction modeling framework.

RESULTS

Despite the absence of residual mitral regurgitation in all postrepair models with optimal neochordae length, selecting an antero-lateral apical entry site for the treatment of P2/P3 prolapse generated a significant increase (>80%) in neochordae tension and P2 peak stress, with respect to a postero-lateral entry site. During isolated P2 prolapse repair, although neochordae overtension by 5% led to minimal hemodynamic changes in the regurgitant volume compared with using an optimal suture length, a significant increase in systolic and diastolic neochordae tension (>300%) and posterior leaflet average stress (70%-460%) was quantified. On the other hand, neochordae undertension by 5% led to worsening of regurgitation severity.

CONCLUSIONS

This parametric computer study represents a further step toward an improved understanding of the biomechanical outcomes of transapical neochordae technologies.

A workflow for patient-specific fluid-structure interaction analysis of the mitral valve: A proof of concept on a mitral regurgitation case

The mechanics of the mitral valve (MV) are the result of the interaction of different anatomical structures complexly arranged within the left heart (LH), with the blood flow. MV structure abnormalities might cause valve regurgitation which in turn can lead to heart failure. Patient-specific computational models of the MV could provide a personalised understanding of MV mechanics, dysfunctions and possible interventions. In this study, we propose a semi-automatic pipeline for MV modelling based on the integration of state-of-the-art medical imaging, i.e. cardiac magnetic resonance (CMR) and 3D transoesophageal-echocardiogram (TOE) with fluid-structure interaction (FSI) simulations. An FSI model of a patient with MV regurgitation was implemented using the finite element (FE) method and smoothed particle hydrodynamics (SPH). Our study showed the feasibility of combining image information and computer simulations to reproduce patient-specific MV mechanics as seen on medical images, and the potential for efficient in-silico studies of MV disease, personalised treatments and device design.

Transcatheter mitral valve chord repair

The field of mitral valve disease diagnosis and management is rapidly evolving. New understanding of pathophysiology and improvements in the adoption of sophisticated multimodality imaging modalities have led to early diagnosis and to more complex treatment. The most common cause of mitral regurgitation (MR) in the western world is in the primary alteration of the valve, which leads to degenerative leaflet prolapse due to chordal elongation or rupture and annular dilatation. Untreated, significant MR has a negative impact prognosis, leading to reduction of survival. In the setting of degenerative MR, surgical repair currently represents the standard of care. Treatment of asymptomatic patients with severe MR in the Valve Center of Excellence, in which successful repair reaches more than 95% and surgical mortality less than 1%, symbolizes the direction for the next years. Transcatheter mitral valve repair with different devices, more recently the chordal replacement ones, is providing good outcomes and became a therapeutic option in high-risk patients with degenerative MR. In the future, more advances are expected from further development of interventional techniques, careful evaluation and better patient selection. This review will focus on long-term surgical outcomes of mitral valve repair with artificial chordae and on the emerging transcatheter chordal repair devices as therapeutic options for degenerative MR patients.

A Swine Model of Percutaneous Intracoronary Ethanol Induced Acute Myocardial Infarction and Ischemic Mitral Regurgitation

Ischemic mitral regurgitation (IMR) is a frequent complication after a myocardial infarction (MI), which doubles mortality. Transcatheter mitral repairs are emerging as alternative treatment options to open heart surgery for IMR, but animal models to test them are lacking. We report a percutaneous swine model of IMR. Seventeen swine were randomized to (group 1, n = 12) MI causing IMR, and (group 2, n = 5) controls. In group 1, MI was induced via percutaneous ethanol injection into the obtuse marginal branches of the left circumflex artery, resulting in ST elevating myocardial infarction. Nine animals were survived to 8-10 weeks with weekly echocardiograms and three swine were survived to 16-20 weeks with MRI at termination. In group 1 animals, average IMR fraction at termination was 26.6 ± 2.3% in the echo group, and 24.51 ± 0.41% in the MRI group. None of the animals in group 2 had IMR. Left ventricular dysfunction and significant dilatation were evident in group 1 animals, compared to the controls. In conclusion, a reproducible model of IMR is reported for use in pre-clinical testing of new mitral technologies.