Page 131 - Read Online

Page 2 of 10 Prescott et al. Vessel Plus 2019;3:13 I http://dx.doi.org/10.20517/2574-1209.2018.70

Keywords: Finite element, mitral valve, MitraClip, mitral regurgitation, hypertrophic obstructive cardiomyopathy,
hyperelastic model

INTRODUCTION
The mitral valve (MV) is a complex apparatus, mainly consisting of mitral annulus, anterior and posterior
leaflets, chordae tendineae and two sets of papillary muscles. The MV is situated between the left atrium and
the left ventricle, which, under regular healthy conditions, ensures that blood can only flow in one direction.
Therefore, there are two key stages to understand the function of the MV. Firstly, the valve allows blood
to flow from the left atrium to the left ventricle during diastolic ventricular filling, and secondly, the valve
[1]
prevents backflow of blood into the left atrium during systolic ventricular ejection . If the valve is diseased,
it cannot ensure a unidirectional flow of blood into the left ventricle, causing the back flow of blood into the
left atrium during systole, a condition known as mitral regurgitation (MR). There are multiple notable causes
of MR, but this study will focus on posterior leaflet prolapse and ruptured chordae tendineae in the context
[2]
of hypertrophic obstructive cardiomyopathy (HOCM) .
A population-based study into the burden of valvular heart diseases highlighted that MR is the most
common heart disease in the western population, and the prevalence of the disease rose strikingly with
[3]
advancing age . For this reason, there is a lot of interest in developing safer and more repeatable procedures
for the treatment of MR. More specifically, there is a push to develop procedures which are less invasive than
conventional open-chest surgery, as a large number of patients (as many as 49%) with MR in need of repair
or replacement are considered at high risk for surgical intervention . Reasons for this high risk association
[4]
can be due to the patients’ age and other comorbidities (the presence of additional diseases co-occurring
with the primary disease) and the result is that the patients simply do not qualify for conventional open-
[5]
chest surgery .
The MitraClip system is a minimally invasive procedure to treat MR in the case where a patient isn’t eligible
for open-chest surgery. Unlike conventional surgery, the MitraClip procedure does not require opening of
the chest. Instead, clinicians access the MV with a catheter that is guided through a vein in the patient’s
[6]
leg to reach the heart . There are also a lot of cases which suggest that the MitraClip system is in fact an
effective approach for the treatment of severe MR in practice. The initial Egyptian experience study into
percutaneous mitral repair with MitraClip system demonstrated that, out of five patients, procedural
success was achieved in all patients (100%). There was no procedural mortality after 30 days. In addition to
[7]
the reduction in MR severity, the clinical status improved in 4 patients (80%) at discharge . Furthermore,
the initial French experience provided additional evidence to support the positive effects of MitraClip
implantation. The study was based on the treatment of 62 patients (72.7 ± 11.4 years; 71.7% men; New
York Heart Association (NYHA) class III or IV; MR ≥ grade 3) and assessed their conditions pre and post
treatment. The study concluded that the in-hospital mortality rate was 3.2%, survival rate at 6 month follow
[8]
up was 83.1%, with 90.9% of patients in NYHA class I or II and residual MR ≤ grade 2 in 80% of cases .
So, despite being an initial learning phase, the results should be seen as promising for the patients who are
ineligible for open-chest surgery. That being said, there is a clear indication for further improvement of the
MitraClip system, particularly the use of simulation work and clinical trials to further understand the MV
and its interaction with the MitraClip.

Therefore, the aim of this paper is to investigate the effects of MitraClip implantation on regurgitant MV
function, in terms of the valve’s ability to close entirely during systole as well as stress distribution across the
valve leaflets at peak systole and diastole, in a finite element (FE) environment.