Transcatheter Mitral Valve Axial Fatigue Testing

As transcatheter aortic valve replacements are rapidly becoming an established treatment option, cardiology’s focus has shifted to the next frontier, Transcatheter Mitral Valve Repair (TMVR).

TMVR是一种微创技术，适合治疗不接受手术的二尖瓣反流的患者。二尖瓣反流可以是初级（退行性的），并且由内在阀病理学或次要阀门病理或次级（功能）引起，在这种情况下，传单是正常的，但不适当地进行缔结。

For a great review of transcatheter mitral valve replacements, you might be interested in an article by the克利夫兰诊所Journal of Medicine (Krishnaswamy A. et al., Vol. 83, Suppl. 2, 2016).

While pulsatile durability testing is often the primary test that comes to mind, axial fatigue testing of valve repair components serves as a very useful tool in characterizing the durability of individual components. Device manufacturers are developing innovative solutions for the transcatheter challenge by utilizing multi-component designs that need to be thoroughly tested.

ISO 5840-3:2013, Cardiovascular implants – Cardiac valve prostheses – Part 3: Heart valve substitutes implanted by transcatheter techniques, offers some guidance on valve testing, including the target number of cycles for fatigue loading. The standard states that testing shall demonstrate that the support structure will remain functional for a minimum of 400 million cycles for critical loading modes. The US Food and Drug Administration (FDA), however, recommends 600 million cycles (Heart Valves: From Design to Clinical Implantation, Iaizzo P. et al., 2013 Edition, Springer). These cycle counts are equivalent to 10 years (400 million cycles) and 15 years (600 million cycles) of implantation in patients.

Transcatheter Mitral Valve Test Protocol

TMVR components that are subject to axial fatigue testing vary depending on the device design. They include the support structure, sutures, clips, occluders, stents or any other components used for anchoring. Axial fatigue testing is typically tensile-to-tensile or slack-to-tensile. In most cases, devices are tested to 600 million cycles, although sometimes testing is first carried out to 400 million cycles and then extended to 600 million cycles upon successful completion of the first step.

Due to the high number of device components typically tested, often in the 10 to 40 sample range depending on the manufacturer’s requirements, we use multi-specimen fixtures mounted on a 3200 or 3300 ElectroForce® Test Instrument. Due to their design geometry, these fixtures are also referred to as spider fixtures. The images below show a generic 15-specimen spider fixture on the left and an example of TMVR attachment fittings/stations added to the fixture on the right.

许多测试都在负载控制中运行，其中您命令执行器以达到指定的负载级别。对于使用多样本夹具的精确负载控制实验，我们使用每样本的单个称重率。在测试样品安装到其站后，每个称重传感器被焦化为零。在每个站点使用调整，然后在测试开始之前都将负载转到相同的级别。在整个测试期间，可能需要在初始预处理循环期间进行额外的调整。

下图显示了具有10样本夹具和各个称重块的TMVR的4000万循环载荷控制测试的示例。它还显示了目标最小和最大负载水平，以及每个样本的负载随时间都发生变化。

Samples are immersed in phosphate-buffered saline solution heated to 37±2°C in a bath, and temperature is recorded throughout testing. The ElectroForce® Test Instruments have very high dynamic performance which allows accelerated loading to high frequencies. Most of these component fatigue tests run in the 40-60 Hz frequency range. A 600-million cycle test at 40 Hz will take approximately 174 days to complete.

在一些TMVR设计中，支架用于锚固装置。在轴向疲劳中测试支架的一种方法是通过提取支架的代表性部分，将其缩进并将其夹在平板上。通常通过有限元分析来完成支架部分选择，以确保它是合适的支架代理。将支架夹紧在平板上的两个主要目的：1）它以平坦的构造保持支架部分，2）它防止支架部分的刚体运动响应于施加的负载。下图显示了3200电磁炉测试仪，具有多试样夹具和用于支架附件的平板。

使用显微镜，内窥镜，频闪光和高速视频在测试之前和之后通常发生样本检查。验收标准由设备制造商定义，设备将返回给客户以进行进一步的分析和测试。

As TMVR designs are being added as an alternative for patients who are not suited for open surgery, axial fatigue testing of device components provides pertinent information for regulatory submissions. Our expertise in cardiovascular device durability testing and in custom fixture design is well-suited for TMVR devices that are often complex.

元素提供最广泛的医疗设备测试范围，因此如果您正在寻找额外的设备测试服务，如包装测试，微生物测试，加速保质期测试或EMC / EMI测试，联系我们与合适的实验室连接。