1Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan.
2Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts.
J Neurosurg. 2020 Feb 28;134(3):893-901. doi: 10.3171/2019.12.JNS192187. Print 2021 Mar 1.
This study's purpose was to improve understanding of the forces driving the complex mechanical interaction between embolic material and current stroke thrombectomy devices by analyzing the histological composition and strength of emboli retrieved from patients and by evaluating the mechanical forces necessary for retrieval of such emboli in a middle cerebral artery (MCA) bifurcation model.
Embolus analogs (EAs) were generated and embolized under physiological pressure and flow conditions in a glass tube model of the MCA. The forces involved in EA removal using conventional endovascular techniques were described, analyzed, and categorized. Then, 16 embolic specimens were retrieved from 11 stroke patients with large-vessel occlusions, and the tensile strength and response to stress were measured with a quasi-static uniaxial tensile test using a custom-made platform. Embolus compositions were analyzed and quantified by histology.
Uniaxial tension on the EAs led to deformation, elongation, thinning, fracture, and embolization. Uniaxial tensile testing of patients' emboli revealed similar soft-material behavior, including elongation under tension and differential fracture patterns. At the final fracture of the embolus (or dissociation), the amount of elongation, quantified as strain, ranged from 1.05 to 4.89 (2.41 ± 1.04 [mean ± SD]) and the embolus-generated force, quantified as stress, ranged from 63 to 2396 kPa (569 ± 695 kPa). The ultimate tensile strain of the emboli increased with a higher platelet percentage, and the ultimate tensile stress increased with a higher fibrin percentage and decreased with a higher red blood cell percentage.
Current thrombectomy devices remove emboli mostly by applying linear tensile forces, under which emboli elongate until dissociation. Embolus resistance to dissociation is determined by embolus strength, which significantly correlates with composition and varies within and among patients and within the same thrombus. The dynamic intravascular weakening of emboli during removal may lead to iatrogenic embolization.
本研究旨在通过分析从患者体内取出的栓子的组织成分和强度，并评估在大脑中动脉（MCA）分叉模型中取出此类栓子所需的机械力，从而深入了解栓塞材料与当前的卒中取栓装置之间复杂机械相互作用的驱动力。
在 MCA 玻璃管模型中，以生理压力和流量条件生成并栓塞栓子模拟物（EAs）。描述、分析和分类了使用常规血管内技术去除 EA 所涉及的力。然后，从 11 名患有大血管闭塞的卒中患者中取出 16 个栓塞标本，并使用定制的平台，通过准静态单轴拉伸试验测量其拉伸强度和对应力的响应。通过组织学分析和量化栓塞物的组成。
EAs 的单轴张力导致变形、伸长、变薄、断裂和栓塞。对患者栓塞物的单轴拉伸测试显示出类似的软物质行为，包括在张力下伸长和不同的断裂模式。在栓塞物的最终断裂（或解离）时，伸长量（定义为应变）的范围为 1.05 至 4.89（2.41±1.04），栓塞物产生的力（定义为应力）的范围为 63 至 2396 kPa（569±695 kPa）。栓塞物的极限拉伸应变随血小板百分比的增加而增加，极限拉伸应力随纤维蛋白百分比的增加而增加，随红细胞百分比的增加而减小。
当前的取栓装置主要通过施加线性拉伸力来移除栓塞物，在此过程中栓塞物会伸长直至解离。栓塞物抵抗解离的能力取决于栓塞物的强度，其与组成显著相关，在患者之间和同一血栓内存在差异。在取出过程中栓塞物的血管内动态弱化可能导致医源性栓塞。
