Abbasi Mostafa, Azadani Ali N
The DU Cardiovascular Biomechanics Laboratory, Department of Mechanical and Materials Engineering, University of Denver, Denver, Colorado, USA.
The DU Cardiovascular Biomechanics Laboratory, Department of Mechanical and Materials Engineering, University of Denver, Denver, Colorado, USA. Electronic correspondence:
J Heart Valve Dis. 2017 Jul;26(4):386-396.
In order to accommodate transcatheter valves to miniaturized catheters, the leaflet thickness must be reduced to a value which is typically less than that of surgical bioprostheses. The study aim was to use finite-element simulations to determine the impact of the thickness reduction on stress and strain distribution.
A 23 mm transcatheter aortic valve (TAV) was modelled based on the Edwards SAPIEN XT (Edwards Lifesciences, Irvine, CA, USA). Finite-element (FE) analysis was performed using the ABAQUS/Explicit solver. An ensemble-averaged transvalvular pressure waveform measured from in-vitro tests conducted in a pulse duplicator was applied to the leaflets. Through a parametric study, uniform TAV leaflet thickness was reduced from 0.5 to 0.18 mm.
By reducing leaflet thickness, significantly higher stress values were found in the leaflet's fixed edge during systole, and in the commissures during diastole. Through dynamic FE simulations, the highest stress values were found during systole in the leaflet fixed edge. In contrast, at the peak of diastole high-stress regions were mainly observed in the commissures. The peak stress was increased by 178% and 507% within the leaflets after reducing the thickness of 0.5 mm to 0.18 mm at the peak of systole and diastole, respectively.
The study results indicated that, the smaller the leaflet thickness, the higher the maximum principal stress. Increased mechanical stress on TAV leaflets may lead to accelerated tissue degeneration. By using a thinner leaflet, TAV durability may not atch with that of surgical bioprostheses.
为了使经导管瓣膜适配小型化导管，瓣叶厚度必须减小到通常小于外科生物瓣膜的厚度值。本研究的目的是使用有限元模拟来确定厚度减小对应力和应变分布的影响。
基于爱德华 Sapien XT（美国加利福尼亚州尔湾市爱德华生命科学公司）对一个 23 毫米的经导管主动脉瓣膜（TAV）进行建模。使用 ABAQUS/Explicit 求解器进行有限元（FE）分析。将从在脉搏复制器中进行的体外测试测量得到的总体平均跨瓣膜压力波形应用于瓣叶。通过参数研究，将 TAV 瓣叶的均匀厚度从 0.5 毫米减小到 0.18 毫米。
通过减小瓣叶厚度，在收缩期瓣叶固定边缘以及舒张期瓣叶连合处发现了显著更高的应力值。通过动态有限元模拟，在收缩期瓣叶固定边缘发现了最高应力值。相比之下，在舒张期峰值时，高应力区域主要出现在瓣叶连合处。在收缩期和舒张期峰值时，将厚度从 0.5 毫米减小到 0.18 毫米后，瓣叶内的峰值应力分别增加了 178%和 507%。
研究结果表明，瓣叶厚度越小，最大主应力越高。TAV 瓣叶上机械应力的增加可能导致组织退变加速。使用更薄的瓣叶，TAV 的耐久性可能无法与外科生物瓣膜相匹配。
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