(F-220) Altered Mechanical and Microstructural Properties of Commercial Bioprosthetic TAVR Valves Following Mechanical Fatigue

Introduction:: Transcatheter aortic valve replacements (TAVR) offer a minimally invasive treatment for aortic stenosis that, through deployment over the patient’s native valve, restore function and alleviate symptoms. The prevalence of TAVR surgeries with respect to standard surgical intervention has continued to increase. However, compared to surgical valves, TAVR valves have an estimated lower longevity, of around 8 years. As GLP cannot be repaired by the hosts cells there is a continual deterioration of the structure due to mechanical fatigue. Studies have been performed in vitro to examine the effects of fatigue on GLP hardness and energy dissipation, collagen fiber orientation and dispersion, and permanent set. Many of these studies utilize uniaxial fatigue due to the ability to control loading or displacement with high accuracy and the relative uniformity of damage within the specimen. However, this is at the cost of physiological relevance which this study aims to address.

Materials and Methods:: The valves analyzed were a Medtronic 26 mm Evolut R valve and a 29 mm Evolut Pro+ valve, and an Edwards 23 mm Sapien XT 9300TFX valve (M26ER, M29EP+, and ES23 respectively). Control material for the M26ER and M29EP+ valves was chosen as the skirt material which is the same material as the leaflets. For the ES23 valve the skirt material is not GLBP and thus the control material was chosen from commercial-grade GLBP acquired from a separate supplier. Digital image correlation (DIC) was used to record the strain on the TAVR valves under physiological pressures. The valve was mounted in a custom test apparatus and a transvalvular pressure of 120 mmHg was applied with the deformation record using two GOM Aramis 12M SRX cameras. DIC imaging was performed before and after AWT for 200 million cycles and areas of high fatigue found by comparing area of greatest strain change. These areas of high fatigue were then isolated for biaxial testing and transmission electron microscopy (TEM).

Results, Conclusions, and Discussions:: For the Medtronic valves DIC showed a reduction in strain post AWT but a statistically significant reduction in mechanical strength. By contrast for the ES23 valve DIC showed an increase in strain post AWT and a reduction in mechanical strength that was not statistically significant. Compared to controls, the TEM shows fragmented and disrupted collagen for M29EP+ and M26ER fatigued leaflets. ES23 fatigued leaflets show little change compared to the control samples. One explanation for the difference in fatigue behavior may be the thinner leaflets in M29EP+ and M26ER valves resulting in increased stress concentrations. This work emphasizes the need for further testing to verify these findings and provide better understanding of the failure pathway. This failure pathway can then be incorporated into the TAVR valve design and selection to improve the system longevity for these devices, of which material properties are one part of a complex system.

Acknowledgements (Optional): : The authors would like to thank the Mayo Clinic Biomechanics and Microscopy and Cell analysis Core Facilities for their assistance in data collection and analysis. This work was supported by the Mayo Clinic Career Development Award in Cardiovascular Diseases Research Honoring Dr. Earl H. Wood and NIH K99HL161272-01A1.

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