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.