Abstract
Background:Transcatheter mitral valve implantation (TMVI) is a promising and minimally invasive treatment for high-risk mitral regurgitation (MR). The purpose of this study was to investigate the feasibility of a novel self-expanding valved stent for transcatheter mitral valve implantation via apical access.
Methods: A novel self-expanding mitral valved stent system was designed and fabricated for the in vivo evaluation. It is consists of an atrial flange and a saddle-shaped ventricular body connected by two opposing anchors and two opposing extensions. During the valve deployment, each anchor is controlled by a recurrent string. TMVI was performed in ten pigs using the valve prosthesis through the apical access to verify technical feasibility. Echocardiography and ventricular angiography were used to assess hemodynamic data and valve function. The surviving pigs were sacrificed four weeks later to confirm stent deployment.
Results:Ten animals underwent transapical mitral valve implantation with the novel mitral valved stent. Optimal valve deployment and accurate anatomical adjustment were obtained in nine animals. Implantation failed in one case, and the animal died one day later due to stent mismatch. After stent implantation, the hemodynamic parameter of other animals was stable and valve function was normal. The mean pressure across the mitral valve and left ventricular outflow tract (LVOT) were 2.98±0.91mmHg and 3.42±0.66 mmHg, respectively. The macroscopic evaluation confirmed the stable and secure positioning of the stents in the mitral valve. No obvious valve displacement, embolism, and paravalvular leakage were observed four weeks after valve implantation.
Conclusions:This study proved that the novel mitral valved valve stent is technically feasible in animals. This device features opposing anchors, opposing recurrent strings, and saddle-like ventricular portions, providing structural design details for reducing TMVI complications. However, the long-term feasibility and durability of this valved stent need to be improved and verified.
INTRODUCTION
Mitral regurgitation(MR) is one of the most prevalent valvular diseases in the world. (1) Surgical mitral replacement is the golden treatment for patients with severe MR, but nearly half of patients with severe MR are rejected. (2) Due to lack of surgical treatment, severe MR patients have a high mortality rate. (3) Transcatheter mitral valve implantation (TMVI) is a minimally invasive treatment for severe MR patients with high surgical risk. (4) The clinical effect of the TMVI device is promising. The Tendyne TMVI system has been approved by the European administration for the treatment of MR(5). Several TMVI devices are undergoing preclinical evaluation or clinical trials, including CardiAQ, Twelve, Tiara, and Fortis. (6) Our team designed a novel TMVI valve stent, which is characterized by two opposing anchors points for grasping native leaflets and two recurrent strings points for accurate valve deployment. A coherent delivery system was designed for the tri-step implantation of the TMVI valve stent through transapical access. The feasibility of the technique was verified by in vivo experiments.
MATERIALS AND METHODS
The novel mitral valved stent system
The valved stent is a self-expanding nitinol stent with bovine pericardial tissue leaflets and biocompatible silicone membrane. (Figure1 A-D) The nitinol stent frame was divided into four parts: atrial side, ventricular body, extensions, and anchors. The height of the valved stent is 20mm and the longest diameter of its ventricular body is 27, 30, 33, and 35mm. The ventricular body is like an inverted cone or saddle, attached by two opposing extensions and two opposing anchors. The extension is triangular, opposed with another, and combined with the ventricular body to reduce the paravalvular leakage. The flange of the atrial side is located at the base of the left atrium and prevents the prosthesis from migrating into the ventricle. The anchor can be abducted by the string while the valve deployment. Two opposing strings stabilize the stent and retrieve it for valve redeployment and readjustment. The structure of the stent is fitted into the complexity of the mitral valve. One anchor is opposite the other and is controlled by a recurrent string, functioning to grasping, engaging, and preserving the native mitral leaflet to avoid valve displacement. The tricuspid pericardial heart valve is mounted on the ventricular body. The nitinol frame is covered with an ultra-thin biocompatible membrane to reduce valve regurgitation.
The valved prosthesis is compressed at the front end of the 28fr delivery system. Each string was loaded inside the delivery system and hung on the anchor in a recurrent direction to control the anchor abduction and stent retrieving. (Figure 1E) Only qualified valve stents are used in animal studies. The releasing and retrieving process of the valved stent system was tested before sterilization.