The Accelerated Transcatheter Heart Valve Testing Environment: Loading, Motion, and Fluid Dynamics.

Transcatheter aortic valve replacements (TAVRs) are an increasingly common treatment for aortic valve disease due to their minimally invasive delivery. As TAVR designs require thinner leaflets to facilitate catheter-based delivery, they experience greater leaflet operational stresses and potentially greater durability issues than conventional surgical valves. Yet, our understanding of TAVR durability remains largely unexplored. Currently, pre-clinical TAVR durability is evaluated within an ISO:5840 compliant accelerated wear tester (AWT) up to a required 200 million cycles, corresponding to approximately five years in vivo. While AWTs use high cycle frequencies (10-20 Hz) to achieve realistic timeframes, the valve loading behaviors and flow are not representative of the in vivo environment and may not accurately predict failure mechanisms. Despite the importance of fatigue and failure predictions for replacement heart valves, surprisingly, little quantitative information exists on the dynamic AWT environment. To better understand this environment, we examined frequency and diastolic period effects for the first time using high-speed enface imaging and particle image velocimetry to quantify valve motion and flow, respectively, using an AWT. Regardless of operating condition, the transvalvular loading pressure never achieved a physiologically relevant mechanical load, thus underloading the TAVR. TAVR motion was also highly sensitive to the operating condition. The flow was consistent with the in vivo environment, but the AWT geometry facilitated secondary flow structures. Therefore, with the non-physiologic loading and variability induced by changes in operating condition, loading criteria must be carefully regulated to ensure physiologically relevant fatigue.