Mitral Valve Mechanics Following Posterior Leaflet Patch Augmentation

Abstract

Background and aim of the study-Attention towards the optimization of mitral valve repair methods is increasing. Patch augmentation is one strategy used to treat functional ischemic mitral regurgitation (FIMR). The study aim was to investigate the force balance changes in specific chordae tendineae emanating from the posterior papillary muscle in a FIMR-simulated valve, following posterior leaflet patch augmentation.Methods-Mitral valves were obtained from 12 pigs (body weight 80 kg). An in vitro test set-up simulating the left ventricle was used to hold the valves. The left ventricular pressure was regulated with water to simulate different static pressures during valve closure. A standardized oval pericardial patch (17 × 29 mm) was introduced into the posterior leaflet from mid P2 to the end of the P3 scallop. Dedicated miniature transducers were used to record the forces exerted on the chordae tendineae. Data were acquired before and after 12 mm posterior and 5 mm apical posterior papillary muscle displacement to simulate the effect from one of the main contributors of FIMR, before and after patch augmentation.Results-The effect of displacing the posterior papillary muscle induced tethering on the intermediate chordae tendineae to the posterior leaflet, and resulted in a 39.8% force increase (p = 0.014). Posterior leaflet patch augmentation of the FIMR valve induced a 31.1% force decrease (p = 0.007). There was no difference in force between the healthy and the repaired valve simulations (p = 0.773).Conclusion-Posterior leaflet patch augmentation significantly reduced the forces exerted on the intermediate chordae tendineae from the posterior papillary muscle following FIMR simulation. As changes in chordal tension lead to a redistribution of the total stress exerted on the valve, patch augmentation may have an adverse long-term influence on mitral valve function and remodeling.

Utilization of Engineering Advances for Detailed Biomechanical Characterization of the Mitral–Ventricular Relationship to Optimize Repair Strategies: A Comprehensive Review

“…For ex vivo modelling, several groups have constructed and published inventive left heart simulators in which the MV can be investigated under approximated physiologic con-ditions [6,13,[27][28][29][30][31][32][33]. In these models, MVs are explanted from porcine or ovine hearts and sutured onto annular and PM mounts that can be inserted into the ex vivo heart simulator.…”

“…These simulators can be based on closed-loop pulsatile pump systems that can produce flow and pressure wave forms close to human physiologic conditions, where the pressure in the "LV" chamber mainly drives MV opening and closing [29,[34][35][36][37][38][39]. More recently, systems focusing on static conditions where the geometry of the MV at peak systolic pressure is modeled have been developed [27,33]. While static PMs have presented a limitation of ex vivo MV modeling for decades, Imbrie-Moore et al recently revolutionized the field by engineering robotic PM mounts for their ex vivo simulator, and were able to mimic 3-dimensional PM movement throughout the cardiac cycle [32].…”

“…In vitro and in vivo models have, to-date, mostly consisted of an isolated flail of a leaflet portion through primary chord severing [146,147]. Attempts to create a model of MVP using mitral leaflet augmentation with pericardial patches to increase the leaflet surface area with no change to the annular size showed that enlargement of the leaflet surface area decreased the secondary chordal forces relative to the native state [9,33,148]. However, these decreases were linked to a change in the relative location of the secondary chordae relative to the coaptation zone: all the models analyzed displayed an increase in leaflet coaptation and secondary chordal insertion sites closer to the coaptation zone-this likely decreased the net forces exerted on the PMs due to a counterbalancing effect on the transduced forces by the opposing leaflet.…”