Mattson Alexander R, Zhingre Sanchez Jorge D, Iaizzo Paul A
Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN, USA.
Department of Surgery, University of Minnesota, Minneapolis, MN, USA.
Pacing Clin Electrophysiol. 2018 Dec;41(12):1606-1610. doi: 10.1111/pace.13529. Epub 2018 Nov 11.
Today, there is no manufacturer-supplied retrieval tool for the Micra™ pacemaker (Medtronic, Minneapolis, MN, USA); therefore, off-the-shelf catheters have been employed for retrievals. The proximal retrieval feature of the Micra™ can be snared and the device is then retracted from the myocardium, pulling the device through the tricuspid valve. This study characterizes the potential risks of Micra™ nitinol tine engagement with the tricuspid sub-valvular apparatus.
Fresh human hearts nonviable for transplant (n = 10) were obtained from our regional organ procurement agency (LifeSource, Minneapolis, MN, USA). Micra™ fixation tines were affixed to a linear force transducer. Tines were then engaged in tricuspid chordae tendineae to conduct a constant velocity tensile test. Each test was run until tines disengaged from the chordae tendineae or until they released from the valve apparatus. Subsequently, biomechanical failure properties of the valve apparatus and isolated chordae tendineae were determined using a series of uniaxial tensile tests.
There were no chordal ruptures observed during our Micra™ tine extraction testing. Chordal failure required 15.0 times the force of extracting a single engaged tine, and 9.0 times the force of extracting two engaged tines. The uniaxial stresses required for isolated chordal failure averaged 17.4 N/mm ; failure strains exceeded 150% resting chordal length.
The forces required to rupture tricuspid chordae tendineae significantly exceeded the forces potentially imposed on the chordae during Micra™ device retrievals. We conclude that the fixation tines of the Micra™ device are unlikely to damage the tricuspid apparatus during either implant or retrieval.
目前，美敦力公司（美国明尼阿波利斯）未提供用于Micra™起搏器的厂家配套取出工具；因此，已采用现成的导管进行取出操作。Micra™起搏器的近端取出特征可通过圈套器捕捉，然后将该装置从心肌中撤回，将其拉过三尖瓣。本研究描述了Micra™镍钛合金固定螺旋与三尖瓣瓣下结构接触时的潜在风险。
从我们当地的器官采购机构（美国明尼阿波利斯的生命源公司）获取10颗不可用于移植的新鲜人心脏。将Micra™起搏器的固定螺旋固定在一个线性力传感器上。然后将螺旋与三尖瓣腱索接触，进行恒速拉伸试验。每个试验持续进行，直到螺旋从腱索上脱离或从瓣膜装置上松开。随后，通过一系列单轴拉伸试验确定瓣膜装置和分离的腱索的生物力学失效特性。
在我们的Micra™起搏器螺旋取出测试过程中，未观察到腱索断裂。腱索断裂所需的力是取出单个啮合螺旋所需力的15.0倍，是取出两个啮合螺旋所需力的9.0倍。分离的腱索断裂所需的单轴应力平均为17.4 N/mm²；断裂应变超过静息腱索长度的150%。
三尖瓣腱索断裂所需的力显著超过了Micra™起搏器取出过程中可能施加在腱索上的力。我们得出结论，在植入或取出过程中，Micra™起搏器的固定螺旋不太可能损坏三尖瓣装置。
