Principles of TAVR valve design, modelling, and testing

Abstract

Introduction: Transcatheter aortic valve replacement (TAVR) has emerged as an effective minimally-invasive alternative to surgical valve replacement in medium- to high-risk, elderly patients with calcific aortic valve disease and severe aortic stenosis. The rapid growth of the TAVR devices market has led to a high variety of designs, each aiming to address persistent complications associated with TAVR valves that may hamper the anticipated expansion of TAVR utility. Areas Covered: Here we outline the challenges and the technical demands that TAVR devices need to address for achieving the desired expansion, and review design aspects of selected, latest generation, TAVR valves of both clinically-used and investigational devices. We further review in detail some of the up-to-date modeling and testing approaches for TAVR, both computationally and experimentally, and additionally discuss those as complementary approaches to the ISO 5840–3 standard. A comprehensive survey of the prior and up-to-date literature was conducted to cover the most pertaining issues and challenges that TAVR technology faces. Expert Commentary: The expansion of TAVR over SAVR and to new indications seems more promising than ever. With new challenges to come, new TAV design approaches, and materials used, are expected to emerge, and novel testing/modeling methods to be developed.

New Insights into Valve Hemodynamics

“…Moreover, this type of valve can be more cost-effective than a bioprosthetic valve since it will have a lower rejection rate during the manufacturing process. 16,17 There is a long history of attempts to develop polymeric valves, which failed to receive regulatory approval. 18 Nevertheless, several such devices are currently being developed and have demonstrated promising experimental results.…”

“…18 Nevertheless, several such devices are currently being developed and have demonstrated promising experimental results. 16,[19][20][21][22] However, even if polymeric valves do achieve the hemodynamic capabilities of current bioprosthetic valves-with the durability of mechanical valvestheir inability to grow makes them problematic for pediatric use. Tissue-engineered heart valves may, potentially, be able to adjust to both tissue growth and remodeling, therefore ensuring prolonged durability.…”

“…25,26 In the latest generation of devices, the only US Food and Drug Administration (FDA)approved TAVI devices are the balloon-expandable Sapien 3 Ultra (Edwards Lifesciences Corp., Irvine, CA, USA), the self-expandable Evolut Pro (Medtronic, Minneapolis, MN, USA), and the self-expandable and mechanically locked Lotus Edge (Boston Scientific, Marlborough, MA, USA). 27 In addition to these three devices, numerous other TAVI devices (including the Portico from Abbott, the Acurate Neo from Boston Scientific, and JenaValve's device) have received Conformité Européenne (CE) marks 16 ; however, most of them have been discontinued. While each of the various CE-marked devices has its own advantages, these advantages are usually related to aspects other than valve hemodynamics.…”

“…This adverse hemodynamic outcome has been significantly minimized in the latest-generation devices, from a prevalence in patients of 25% to 5%. 16 This reduction was achieved by adding an outer skirt or cuff that covers the ventricular portion of the stent. In the original Sapien 3 valve, the outer skirt included openings that created pockets that could fill with blood, thereby sealing the paravalvular gaps.…”

“…In the original Sapien 3 valve, the outer skirt included openings that created pockets that could fill with blood, thereby sealing the paravalvular gaps. 16 This design was later refined in the Sapien 3 Ultra valve by increasing the outer skirt height, closing the pockets, and adding texture to the polyethylene terephthalate fabric. While the latest self-expandable devices also have an outer skirt, they can seal the gaps with an optimized anatomical fitting, specifically by having a larger stent diameter on the ventricular side than in the valve region.…”