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An In Vivo Quantification of the Apical Fixation Forces of Different Mitral Valved Stent Designs in the Beating Heart
Saskia Pokorny1, Katharina Huenges1, Telse Bähr1, Alexander Engel1, Martin Marczynski-Bühlow1, Michael M. Morlock2, Jochen Cremer1, Georg Lutter1.
1University Hospital Schleswig-Holstein, Campus Kiel, Department of Cardiovascular Surgery, Kiel, Germany, 2TUHH Hamburg University of Technology, Institute of Biomechanics, Hamburg, Germany.

OBJECTIVE: The aim of this study was the quantification of the apical fixation force of mitral valved stents in an experimental in vivo setting.
METHODS: A test set-up consisting of a force sensor aligned to the stent long axis was developed to quantify the forces acting on the apical fixation of mitral valved stents.
20 pigs (50±2kg) received a self-expanding valved stent in the mitral position via transapical approach in an off-pump procedure. The first design AP (n=10) was solely anchored apically with a fixation system comprised of four neo-chords attached to the ventricular rim of the stent. The second design SA (n=10) included additional sub-annular fixation elements within the ventricular stent body.
Following stent deployment in the beating heart correct stent position was adjusted under control of paravalvular leakages (PVL), mitral annular plane systolic excursion (MAPSE) and pulmonary capillary wedge pressure (PCWP). The neo-chords were attached to the force sensor and forces were recorded during expiratory breath hold following a standardized protocol. Forces were normalized to the mean systolic atrio-ventricular pressure difference.
RESULTS: Force measurement was successfully conducted in 18 of 20 animals (design AP:n=10; design SA:n=8). Two animals were excluded from the evaluation due to non device related ventricular fibrillation prior to stent implantation.
In group AP the mean forces and the amplitude showed a trend to higher forces compared to the group with additional sub-annular fixation elements (p=0.046; Table1). The MAPSE showed good longitudinal heart function in both groups. The PCWP was within physiological range and did not change (p>0.05).
CONCLUSIONS: An intra-procedural force measurement system was developed and the fixation forces acting upon the apical fixation system of mitral valved stents were quantified for the first time. A trend towards lower forces was detected in the group with additional sub-annular fixation. Measurement of the in vivo forces provides important information of the impact of different prototype designs on the heart function as well as information for a later clinical application.
Table 1: Quantification of apical fixation forces
Stent DesignFmaxnorm
[N]
Fminnorm
[N]
Fmeannorm
[N]
ΔF [N]ΔP
[mmHg]
PCWP
[mmHg]
MAPSE
[cm]
Group AP
(n=10)
4.1 ± 1.51.9 ± 1.43.1 ± 1.41.8 ± 1.2*74 ± 611 ± 41.0 ± 0.1
Group SA
(n=8)
3.0 ± 1.01.6 ± 1.12.3 ± 0.91.4 ± 1.1*71 ± 1011 ± 31.0 ± 0.2
Group AP: sole apical fixation; Group SA: additional sub-annular fixation;
Fmax / Fmin / Fmean: maximal, minimal and mean force recorded throughout the heart cycle normalized to the mean ΔP(n=18)=71.9 mmHg;
ΔF: force amplitude
ΔP: left atrio-ventricular pressure gradient (left atrial pressure approximated by mean wedge pressure and left ventricular pressure approximated by maximal arterial pressure); PCWP: pulmonary capillary wedge pressure during force measurement,
MAPSE: mitral annular plane systolic excursion recorded during force measurement
*: statistical significant difference between the two groups with p≤ 0.05


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