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

Ex Vivo Model of Ischemic Mitral Regurgitation and Analysis of Adjunctive Papillary Muscle Repair

Ischemic mitral regurgitation (IMR) is particularly challenging to repair with lasting durability due to the complex valvular and subvalvular pathologies resulting from left ventricular dysfunction. Ex vivo simulation is uniquely suited to quantitatively analyze the repair biomechanics, but advancements are needed to model the nuanced IMR disease state. Here we present a novel IMR model featuring a dilation device with precise dilatation control that preserves annular elasticity to enable accurate ex vivo analysis of surgical repair. Coupled with augmented papillary muscle head positioning, the enhanced heart simulator system successfully modeled IMR pre- and post-surgical intervention and enabled the analysis of adjunctive subvalvular papillary muscle repair to alleviate regurgitation recurrence. The model resulted in an increase in regurgitant fraction: 11.6 ± 1.7% to 36.1 ± 4.4% (p < 0.001). Adjunctive papillary muscle head fusion was analyzed relative to a simple restrictive ring annuloplasty repair and, while both repairs successfully eliminated regurgitation initially, the addition of the adjunctive subvalvular repair reduced regurgitation recurrence: 30.4 ± 5.7% vs. 12.5 ± 2.6% (p = 0.002). Ultimately, this system demonstrates the success of adjunctive papillary muscle head fusion in repairing IMR as well as provides a platform to optimize surgical techniques for increased repair durability.

Biomimetic six-axis robots replicate human cardiac papillary muscle motion: pioneering the next generation of biomechanical heart simulator technology

Papillary muscles serve as attachment points for chordae tendineae which anchor and position mitral valve leaflets for proper coaptation. As the ventricle contracts, the papillary muscles translate and rotate, impacting chordae and leaflet kinematics; this motion can be significantly affected in a diseased heart. In ex vivo heart simulation, an explanted valve is subjected to physiologic conditions and can be adapted to mimic a disease state, thus providing a valuable tool to quantitatively analyse biomechanics and optimize surgical valve repair. However, without the inclusion of papillary muscle motion, current simulators are limited in their ability to accurately replicate cardiac biomechanics. We developed and implemented image-guided papillary muscle (IPM) robots to mimic the precise motion of papillary muscles. The IPM robotic system was designed with six degrees of freedom to fully capture the native motion. Mathematical analysis was used to avoid singularity conditions, and a supercomputing cluster enabled the calculation of the system's reachable workspace. The IPM robots were implemented in our heart simulator with motion prescribed by high-resolution human computed tomography images, revealing that papillary muscle motion significantly impacts the chordae force profile. Our IPM robotic system represents a significant advancement for ex vivo simulation, enabling more reliable cardiac simulations and repair optimizations.

A novel cross-species model of Barlow's disease to biomechanically analyze repair techniques in an ex vivo left heart simulator

OBJECTIVE

Barlow's disease remains challenging to repair, given the complex valvular morphology and lack of quantitative data to compare techniques. Although there have been recent strides in ex vivo evaluation of cardiac mechanics, to our knowledge, there is no disease model that accurately simulates the morphology and pathophysiology of Barlow's disease. The purpose of this study was to design such a model.

METHODS

To simulate Barlow's disease, a cross-species ex vivo model was developed. Bovine mitral valves (n = 4) were sewn into a porcine annulus mount to create excess leaflet tissue and elongated chordae. A heart simulator generated physiologic conditions while hemodynamic data, high-speed videography, and chordal force measurements were collected. The regurgitant valves were repaired using nonresectional repair techniques such as neochord placement.

RESULTS

The model successfully imitated the complexities of Barlow's disease, including redundant, billowing bileaflet tissues with notable regurgitation. After repair, hemodynamic data confirmed reduction of mitral leakage volume (25.9 ± 2.9 vs 2.1 ± 1.8 mL, P < .001) and strain gauge analysis revealed lower primary chordae forces (0.51 ± 0.17 vs 0.10 ± 0.05 N, P < .001). In addition, the maximum rate of change of force was significantly lower postrepair for both primary (30.80 ± 11.38 vs 8.59 ± 4.83 N/s, P < .001) and secondary chordae (33.52 ± 10.59 vs 19.07 ± 7.00 N/s, P = .006).

CONCLUSIONS

This study provides insight into the biomechanics of Barlow's disease, including sharply fluctuating force profiles experienced by elongated chordae prerepair, as well as restoration of primary chordae forces postrepair. Our disease model facilitates further in-depth analyses to optimize the repair of Barlow's disease.

A novel 3D-Printed preferential posterior mitral annular dilation device delineates regurgitation onset threshold in an ex vivo heart simulator

Mitral regurgitation (MR) due to annular dilation occurs in a variety of mitral valve diseases and is observed in many patients with heart failure due to mitral regurgitation. To understand the biomechanics of MR and ultimately design an optimized annuloplasty ring, a representative disease model with asymmetric dilation of the mitral annulus is needed. This work shows the design and implementation of a 3D-printed valve dilation device to preferentially dilate the posterior mitral valve annulus. Porcine mitral valves (n = 3) were sewn into the device and mounted within a left heart simulator that generates physiologic pressures and flows through the valves, while chordal forces were measured. The valves were incrementally dilated, inducing MR, while hemodynamic and force data were collected. Flow analysis demonstrated that MR increased linearly with respect to percent annular dilation when dilation was greater than a 25.6% dilation threshold (p < 0.01). Pre-threshold, dilation did not cause significant increases in regurgitant fraction. Forces on the chordae tendineae increased as dilation increased prior to the identified threshold (p < 0.01); post-threshold, the MR resulted in highly variable forces. Ultimately, this novel dilation device can be used to more accurately model a wide range of MR disease states and their corresponding repair techniques using ex vivo experimentation. In particular, this annular dilation device provides the means to investigate the design and optimization of novel annuloplasty rings.

Tricuspid Valve Annular Mechanics: Interactions with and Implications for Transcatheter Devices

In the interventional treatment of tricuspid valve regurgitation, the majority of prosthetic devices interact with or are implanted to the tricuspid valve annulus. For new transcatheter technologies, there exists a growing body of clinical experience, literature, and professional discourse related to the difficulties in delivering, securing, and sustaining the function of these devices within the dynamic tricuspid annulus. Many of the difficulties arise from circumstances not encountered in open-heart surgery, namely; a non-arrested heart, indirect visualization, and a reliance on non-suture-based methods. These challenges require the application of procedural techniques or system designs to account for tricuspid annular motion, forces, and underlying tissue strength. Improved knowledge in these interactions will support the goals of improving device systems, their procedures, and patient outcomes. This review aims to describe current concepts of tricuspid annular mechanics, key device and procedural implications, and highlight current knowledge gaps for future consideration.

Effects of annular contraction on anterior leaflet strain using an in vitro simulator with a dynamically contracting mitral annulus

Using in vitro models, the mechanics as well as surgical techniques for mitral valves (MV) and MV devices can be studied in a more controlled environment with minimal monetary investment and risk. However, these current models rely on certain simplifications, one being that the MV has a static, rigid annulus. In order to study more complex issues of imaging diagnostics and implanted device function, it would be more advantageous to verify their use for a dynamic environment in a dynamic simulator. This study provides the novel design and development of a dynamically contracting annulus (DCA) within an in vitro simulator, and its subsequent use to study MV biomechanics. Experiments were performed to study the ability of the DCA to reproduce the MV leaflet mechanics in vitro, as seen in vivo, as well as investigate how rigid annuloplasties affect MV leaflet mechanics. Experiments used healthy, excised MVs and normal hemodynamics; contractile waveforms were derived from human in vivo data. Stereophotogrammetry and echocardiography were used to measure anterior leaflet strain and the change in MV geometry. In pursuit of the first in vitro MV simulator that more completely represents the dynamic motion of the full valvular apparatus, this study demonstrated the successful operation of a dynamically contracting mitral annulus. It was seen that the diseased contractile state increased anterior leaflet strain compared to the healthy contractile state. In addition, it was also shown in vitro that simulated rigid annuloplasty increased mitral anterior leaflet strain compared to a healthy contraction.

Modelling of Lesions Associated with Functional Mitral Regurgitation in an Ex Vivo Platform

Functional mitral regurgitation (FMR) is a complex pathology involving valvular and subvalvular structures reconfiguration, and its treatment is considered challenging. There is a lack of experimental models allowing for reliable preclinical FMR treatments' evaluation in a realistic setting. A novel approach to simulate FMR was developed and incorporated into an ex vivo passive beating heart platform. FMR was obtained by dilating the mitral annulus (MA) mainly in the antero-posterior direction and displacing the papillary muscles (PMs) apically and laterally by ad hoc designed and 3D printed dilation and displacing devices. It caused hemodynamic and valve morphology alterations. Isolated MA dilation (MAD) led to significantly increased antero-posterior distance (A-P) and decreased coaptation height (CH), tenting area (TA) and systolic leaflets angulation, resembling clinically recognized type I of mitral regurgitation with normal leaflet motion. Whereas concomitant MAD with PM displacement caused an increase in A-P, TA, CH. This geometrical configuration replicated typical determinants of type IIIb lesion with restricted leaflet motion. The proposed methods provided a realistic and repeatable ex vivo FMR model featuring two lesions clinically associated with the pathology. It bears a promise to be successfully utilized in preclinical studies, clinical training and medical education.