Ismail Munirah, Kumar Gideon Praveen, Kabinejadian Foad, Nguyen Yen Ngoc, Cui Fangsen, Tay Edgar Lik Wui, Leo Hwa Liang
Department of Biomedical Engineering, National University of Singapore, Singapore, Singapore.
Institute of High Performance Computing, A*STAR, Singapore, Singapore.
Cardiovasc Eng Technol. 2016 Sep;7(3):254-69. doi: 10.1007/s13239-016-0268-8. Epub 2016 Jun 29.
Heterotopic implantation of transcatheter tricuspid valve is a new treatment option for tricuspid regurgitation. Transcatheter tricuspid valves are implanted onto the cavoatrial junction in order to avoid the challenging task of anchoring the valve onto the complex tricuspid valve annulus. However, little is known about optimum extent of oversizing of the valved stent in a vena cava. In this study, we implanted valves of the same diameter onto the larger sized inferior vena cava (IVC) and a smaller sized superior vena cava (SVC). The valve in the IVC was oversized by 10.7% while the valve in the SVC was oversized by 21.6%. Finite element analysis was performed (i) to assess the strain on the nitinol stent during manufacturing and deployment; (ii) the stents were deployed in a patient-specific vena cava model and the intramural stress of the vena cava was calculated computationally. These valves were fabricated and placed in a silicone model of a patient-specific right atrium which was part of a mock circulatory system that emulated the patho-physiological flow rate and pressure of a patient with tricuspid regurgitation. Flow measurements were conducted by particle image velocimetry (PIV). It was found that the maximum crimping strain on the nitinol stent was 6.85% which was lower than the critical threshold of 10%. The maximum stress on the vena cava was located at the spot where the hooks met the wall. The maximum stress on the IVC was 0.5098 MPa while the maximum stress on the SVC was 0.7 MPa. The maximum Reynolds shear stress (mRSS) in the vena cava was found to be higher in the IVC than SVC with the highest mRSS being 1741 dynes/cm(2) found in the region of high flow during the peak flow phase. The overtly oversized valve in the SVC did not cause flow disturbances and exhibited mostly laminar flows. The mRSS at the downstream of the vena cava valve and the middle of the atrium remained at low magnitudes. However, velocity fluctuations were high in the IVC in all the time points measured. In conclusion, oversizing the valve may assist anchorage; yet, careful consideration should be taken in choosing the extent of oversizing as it may lead to adverse effects.
经导管三尖瓣异位植入是三尖瓣反流的一种新治疗选择。经导管三尖瓣被植入腔静脉心房交界处，以避免将瓣膜固定在复杂的三尖瓣环上这一具有挑战性的任务。然而，对于腔静脉中带瓣支架的最佳超大尺寸范围知之甚少。在本研究中，我们将相同直径的瓣膜植入较大尺寸的下腔静脉（IVC）和较小尺寸的上腔静脉（SVC）。IVC中的瓣膜超大尺寸为10.7%，而SVC中的瓣膜超大尺寸为21.6%。进行了有限元分析：（i）评估镍钛诺支架在制造和展开过程中的应变；（ii）将支架部署在患者特异性腔静脉模型中，并通过计算得出腔静脉的壁内应力。这些瓣膜被制造出来并放置在患者特异性右心房的硅胶模型中，该模型是模拟三尖瓣反流患者病理生理流速和压力的模拟循环系统的一部分。通过粒子图像测速法（PIV）进行流量测量。发现镍钛诺支架上的最大卷曲应变为6.85%，低于10%的临界阈值。腔静脉上的最大应力位于挂钩与壁接触的位置。IVC上的最大应力为0.5098兆帕，而SVC上的最大应力为0.7兆帕。发现腔静脉中的最大雷诺剪切应力（mRSS）在IVC中高于SVC，在峰值流量阶段高流量区域中发现的最高mRSS为1741达因/平方厘米。SVC中明显超大尺寸的瓣膜未引起流量干扰，且大多呈现层流。腔静脉瓣膜下游和心房中部的mRSS保持在较低水平。然而，在所有测量的时间点，IVC中的速度波动都很高。总之，瓣膜超大尺寸可能有助于固定；然而，在选择超大尺寸范围时应谨慎考虑，因为这可能会导致不良影响。
