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

Abstract

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, preclinical TAVR durability is evaluated within an ISO:5840 compliant accelerated wear tester (AWT) up to a required 200 × 106 cycles, corresponding to approximately five years in vivo. While AWTs use high cycle frequencies (10–20 Hz) to achieve realistic timeframes, the resulting valve loading behaviors and fluid dynamics are not representative of the in vivo environment and thus 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 a Durapulse™ AWT at frequencies of 10, 15, and 20 Hz. Regardless of operating condition, no waveform achieved a physiologically relevant transvalvular loading pressure, despite having an ISO compliant geometric orifice area (GOA) and waveform. General fluid mechanics were consistent with in vivo but the AWT geometry developed secondary flow structures, which could impact mechanical loading. Therefore, the nonphysiologic loading and variability induced by changes in operating condition must be carefully regulated to ensure physiologically relevant fatigue.