Zhou Li, Bar-Cohen Yaniv, Peck Raymond A, Chirikian Giorgio V, Harwin Brett, Chmait Ramen H, Pruetz Jay D, Silka Michael J, Loeb Gerald E
Medical Device Development Facility, Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, 1042 Downey Way, Los Angeles, CA, 90089, USA.
Division of Cardiology, Department of Pediatrics, Keck School of Medicine, Children's Hospital Los Angeles, University of Southern California, 4650 Sunset Blvd, Los Angeles, CA, 90027, USA.
Cardiovasc Eng Technol. 2017 Mar;8(1):96-105. doi: 10.1007/s13239-017-0292-3. Epub 2017 Jan 9.
Implantation and maintenance of a permanent cardiac pacing system in children remains challenging due to small patient size, congenital heart defects and somatic growth. We are developing a novel epicardial micropacemaker for children that can be implanted on the epicardium within the pericardial space via a minimally-invasive technique. The key design configurations include a novel open-coiled lead in which living tissue replaces the usual polymeric support for the coiled conductor. To better understand and be able to predict the behavior of the implanted lead, we performed a radiographic image-based modeling study on a chronic animal test. We report a pilot study in which two mechanical dummy pacemakers with epicardial leads were implanted into an adult pig model via a minimally invasive approach. Fluoroscopy was obtained on the animal on Post-Operative Days #9, #35 and #56 (necropsy). We then constructed an analytic model to estimate the in vivo stress conditions on the open-coil lead based on the analysis of orthogonal biplane radiographic images. We obtained geometric deformation data of the implanted lead including elongation magnitudes and bending radii from sequenced films of cardiac motion cycles. The lead stress distribution was investigated on each film frame and the point of maximum stress (Mean Stress = 531.4 MPa; Alternating Stress = ± 216.4 MPa) was consistently where one of the leads exited the pericardial space, a deployment that we expected to be unfavorable. These results suggest the modeling approach can provide a basis for further design optimization. More animal tests and modeling will be needed to validate whether the novel lead design could meet the requirements to withstand ~200 million cardiac motion cycles over 5 years.
由于儿童患者体型小、存在先天性心脏缺陷以及身体生长发育等因素，在儿童体内植入并维持永久性心脏起搏系统仍然具有挑战性。我们正在为儿童研发一种新型的心外膜微型起搏器，该起搏器可通过微创技术植入心包腔内的心外膜上。关键设计结构包括一种新型的开放式螺旋导线，其中活组织取代了通常用于螺旋导体的聚合物支撑材料。为了更好地理解并能够预测植入导线的行为，我们在一项慢性动物试验中进行了基于放射图像的建模研究。我们报告了一项初步研究，其中将两个带有心外膜导线的机械模拟起搏器通过微创方法植入成年猪模型中。在术后第9天、第35天和第56天（尸检）对动物进行荧光透视检查。然后，我们构建了一个分析模型，基于对正交双平面放射图像的分析来估计开放式螺旋导线上的体内应力状况。我们从心脏运动周期的序列胶片中获得了植入导线的几何变形数据，包括伸长量和弯曲半径。在每个胶片帧上研究导线应力分布，最大应力点（平均应力 = 531.4兆帕；交变应力 = ±216.4兆帕）始终位于其中一根导线穿出心包腔的位置，这种布置我们预计是不利的。这些结果表明，该建模方法可为进一步的设计优化提供基础。需要更多的动物试验和建模来验证这种新型导线设计是否能够满足在5年内承受约2亿次心脏运动周期的要求。
