Transapical Coaptation Plate for Functional Mitral Regurgitation: An In Vitro Study

A novel transapical coaptation plate (TCP) device was developed and anchored by sutures in the mitral valve to treat functional mitral regurgitation. The objective of this study was to test efficacy of the TCP in an in vitro model. Eight fresh porcine mitral valves were mounted in a left heart simulator to simulate functional mitral regurgitation by means of annular dilatation and asymmetrical or symmetrical papillary muscle (PM) displacement. Six polyurethane TCPs in thickness of 6.4(#1), 4.8(#2), 3.2(#3) mm and hardness of durometer 30 A (H) and 30 OO(S),were fabricated and labeled as H1, H2, H3 and S1, S2, S3, respectively. These TCPs were anchored by the sutures in the mitral annulus and left ventricle apex, and tested. Steady backward flow leakage in a hydrostatic condition and regurgitant volume in a pulsatile flow were measured before and after implantation of the TCPs. Mean regurgitant volume fractions in the asymmetric PM displacement were reduced significantly from 59.1 to 37.2% for H1, 43.2% for H2, 35.9% for S1 and 34.2% for S2 (p < 0.021), after implantation of the TCPs. No significant reduction in mitral regurgitation was seen for H3 and S3 (p > 0.067). Mitral regurgitation was mild in the symmetric PM displacement, and was not significantly reduced after implantation of the TCPs. In conclusion, the TCP anchored by the sutures in the mitral annulus and left ventricle apex functions successfully as a plug in the mitral valve leaflet gap. The TCP with thickness equal to or greater than 4.8 mm is effective to reduce functional mitral regurgitation. The TCP hardness has no effect on difference in reduction of functional mitral regurgitation.

Bench Models for Assessing the Mechanics of Mitral Valve Repair and Percutaneous Surgery

Rapid preclinical evaluations of mitral valve (MV) mechanics are currently best facilitated by bench models of the left ventricle (LV). This review aims to provide a comprehensive assessment of these models to aid interpretation of their resulting data, inform future experimental evaluations, and further the translation of results to procedure and device development. For this review, two types of experimental bench models were evaluated. Rigid LV models were characterized as fluid-mechanical systems capable of testing explanted MVs under static and or pulsatile left heart hemodynamics. Passive LV models were characterized as explanted hearts whose left side is placed in series with a static or pulsatile flow-loop. In both systems, MV function and mechanics can be quantitatively evaluated. Rigid and passive LV models were characterized and evaluated. The materials and methods involved in their construction, function, quantitative capabilities, and disease modeling were described. The advantages and disadvantages of each model are compared to aid the interpretation of their resulting data and inform future experimental evaluations. Repair and percutaneous studies completed in these models were additionally summarized with perspective on future advances discussed. Bench models of the LV provide excellent platforms for quantifying MV repair mechanics and function. While exceptional work has been reported, more research and development is necessary to improve techniques and devices for repair and percutaneous surgery. Continuing efforts in this field will significantly contribute to the further development of procedures and devices, predictions of long-term performance, and patient safety.

A novel coaptation plate device for functional mitral regurgitation: an in vitro study

A novel mitral valve repair device, coaptation plate (CP), was proposed to treat functional mitral regurgitation. The objective of this study was to test efficacy of the CP in an in vitro model of functional mitral regurgitation. Ten fresh porcine mitral valves were mounted in a left heart simulator, Mitral regurgitation was emulated by means of annular dilatation, and the asymmetrical or symmetrical papillary muscles (PM) displacement. A rigid and an elastic CPs were fabricated and mounted in the orifice of regurgitant mitral valves. Steady flow leakage in a hydrostatic condition and regurgitant volume in a pulsatile flow were measured before and after implantation of the CPs. The rigid and elastic CPs reduced mitral valve regurgitant volume fraction from 60.5 ± 11.4 to 35 ± 11.6 and 36.5 ± 9.9%, respectively, in the asymmetric PM displacement. Mitral regurgitation was much lower in the symmetric PM displacement than in the asymmetric PM displacement, and was not significantly reduced after implantation of either CP. In conclusion, both the rigid and elastic CPs are effective and have no difference in reduction of functional mitral regurgitation. The CP does not aggravate mitral valve coaptation and may be used as a preventive way.

Functional and Biomechanical Effects of the Edge-to-Edge Repair in the Setting of Mitral Regurgitation: Consolidated Knowledge and Novel Tools to Gain Insight into Its Percutaneous Implementation

Mitral regurgitation is the most prevalent heart valve disease in the western population. When severe, it requires surgical treatment, repair being the preferred option. The edge-to-edge repair technique treats mitral regurgitation by suturing the leaflets together and creating a double-orifice valve. Due to its relative simplicity and versatility, it has become progressively more widespread. Recently, its percutaneous version has become feasible, and has raised interest thanks to the positive results of the Mitraclip(®) device. Edge-to-edge features and evolution have stimulated debate and multidisciplinary research by both clinicians and engineers. After providing an overview of representative studies in the field, here we propose a novel computational approach to the most recent percutaneous evolution of the edge-to-edge technique. Image-based structural finite element models of three mitral valves affected by posterior prolapse were derived from cine-cardiac magnetic resonance imaging. The models accounted for the patient-specific 3D geometry of the valve, including leaflet compound curvature pattern, patient-specific motion of annulus and papillary muscles, and hyperelastic and anisotropic mechanical properties of tissues. The biomechanics of the three valves throughout the entire cardiac cycle was simulated before and after Mitraclip(®) implantation, assessing the biomechanical impact of the procedure. For all three simulated MVs, Mitraclip(®) implantation significantly improved systolic leaflets coaptation, without inducing major alterations in systolic peak stresses. Diastolic orifice area was decreased, by up to 58.9%, and leaflets diastolic stresses became comparable, although lower, to systolic ones. Despite established knowledge on the edge-to-edge surgical repair, latest technological advances make its percutanoues implementation a challenging field of research. The modeling approach herein proposed may be expanded to analyze clinical scenarios that are currently critical for Mitraclip(®) implantation, helping the search for possible solutions.

Annulus tension of the prolapsed mitral valve corrected by edge-to-edge repair

BACKGROUND

Mitral valve (MV) performance after edge-to-edge repair (ETER) without ring annuloplasty is suboptimal. ETER efficacy needs to be evaluated from annulus tension (AT) of a prolapsed MV corrected by ETER to understand annular dilatation.

METHODS

Ten porcine MVs were harvested and mounted on a MV closure test rig. The MV annulus tissue rested on top of a saddle-shaped plastic ring on which the annulus could slide freely. The annulus was held by strings in the periphery during MV closure under a hydrostatic trans-mitral pressure. String tensions were measured and further divided by string spacing to obtain AT. The MVs were then prolapsed by shifting split papillary muscles to simulate mono-leaflet prolapse due to elongation of chords, which insert into a single leaflet. Last, MV prolapse was corrected by ETER applied in the central leaflet region and AT was measured.

RESULTS

AT in both anterior and posterior leaflet prolapse corrected by ETER was less than that of normal MVs. AT in the anterior leaflet prolapse corrected by ETER was less than that in the posterior leaflet prolapse corrected by ETER.

CONCLUSION

ETER does not restore the normal AT and therefore leads potential of annular dilatation. The anterior leaflet prolapse has a greater potential of annular dilatation than the posterior leaflet prolapse after ETER. Annuloplasty is recommended to maintain long-term ETER efficacy.

A pulsatile simulator for the in vitro analysis of the mitral valve with tri-axial papillary muscle displacement

PURPOSE

We developed a new pulsatile hydrodynamic simulator for the in vitro testing of mitral valve (MV) samples. The required specifications included a 3D positioning system for the papillary muscles (PMs) that is accurate and simple to manage; measurement of the force exerted by the chordae tendineae on the PMs; and the possibility to visually inspect the MV for kinematic analysis.

METHODS

An atrial/ventricular chamber system was developed. The ventricular chamber housed a tri-axial actuator system that was aligned to a morphometric Cartesian frame, allowing for PM positioning even while tests are running. Each PM holder had an embedded load cell for force measurement. The atrial chamber was designed so as to permit MV visual inspection, maintaining a non-disturbed flow at the sample inlet. The setup was subjected to trials with fresh porcine MVs. Flow and pressure difference across the MVs and PM forces were measured in different MV configurations, with different PM spatial dislocations. High speed video recordings were acquired.

RESULTS

The positioning accuracy was assessed. Tests with MVs showed good usability, even by the non-engineering personnel. The effects of PM displacement on valve function (valve competence and PM forces) was consistent with previously published data, thus confirming the general soundness of the design principles.

CONCLUSIONS

The developed simulator is a promising instrument for performing MV in vitro tests in a precise, well-repeatable manner. The ability to completely adjust the PM position while a test is running boosts the simulator's potential for detailed investigations of the pathological and surgically treated MV.