Abstract
Leaflet durability and costs restrict contemporary trans-catheter aortic valve replacement (TAVR) largely to elderly patients in affluent countries. TAVR that are easily deployable, avoid secondary procedures and are also suitable for younger patients and non-calcific aortic regurgitation (AR) would significantly expand their global reach. Recognizing the reduced need for post-implantation pacemakers in balloon-expandable (BE) TAVR and the recent advances with potentially superior leaflet materials, a trans-catheter BE-system was developed that allows tactile, non-occlusive deployment without rapid pacing, direct attachment of both bioprosthetic and polymer leaflets onto a shape-stabilized scallop and anchorage achieved by plastic deformation even in the absence of calcification. Three sizes were developed from nickel-cobalt-chromium MP35N alloy tubes: Small/23 mm, Medium/26 mm and Large/29 mm. Crimp-diameters of valves with both bioprosthetic (sandwich-crosslinked decellularized pericardium) and polymer leaflets (triblock polyurethane combining siloxane and carbonate segments) match those of modern clinically used BE TAVR. Balloon expansion favors the wing-structures of the stent thereby creating supra-annular anchors whose diameter exceeds the outer diameter at the waist level by a quarter. In the pulse duplicator, polymer and bioprosthetic TAVR showed equivalent fluid dynamics with excellent EOA, pressure gradients and regurgitation volumes. Post-deployment fatigue resistance surpassed ISO requirements. The radial force of the helical deployment balloon at different filling pressures resulted in a fully developed anchorage profile of the valves from two thirds of their maximum deployment diameter onwards. By combining a unique balloon-expandable TAVR system that also caters for non-calcific AR with polymer leaflets, a powerful, potentially disruptive technology for heart valve disease has been incorporated into a TAVR that addresses global needs. While fulfilling key prerequisites for expanding the scope of TAVR to the vast number of patients of low- to middle income countries living with rheumatic heart disease the system may eventually also bring hope to patients of high-income countries presently excluded from TAVR for being too young.
Highlights
During several decades of development, transcatheter aortic valve replacement almost exclusively focused on the treatment of calcific aortic stenosis (AS) [1–4]
The design of the TAVR stent was based on three principles: [1] continual stent-scallops for leaflet attachment that are crimpable and restored to their original shape upon balloon expansion; [2] self-elevating inter-commissural anchoring arms based on geometric changes due to plastic deformation occurring after crimping during deployment and [3] an hourglass shape with the waist seated in the annulus plane resulting in a concavity around the bulge of the crest of the muscular ventricular septum, easing the pressure on the crest [24, 25]
The BE TAVR system met all requirements for which it was developed: the expansion-linked shape-change of the stent resulted in the profile differences required for anchorage in non-calcified aortic roots; the scallop-design allowed for the direct, fatigue-resistant attachment of both elastomeric and bioprosthetic leaflets and the deployment device permitted
Summary
During several decades of development, transcatheter aortic valve replacement almost exclusively focused on the treatment of calcific aortic stenosis (AS) [1–4]. Since in highincome countries (HIC) where TAVR was pioneered [1, 5], pure aortic regurgitation (AR) occurs less frequently than AS [4, 6, 7] pure AR did not have enough traction to influence developments. This is still reflected in contemporary TAVR designs whose simple mesh structures are sufficient to anchor the stents in the rigid calcific deposits of AS. Given the huge global burden of rheumatic heart disease (RHD) in emerging economies [8–10] with its predominance of AR [9– 13] and the growing number of patients with pure AR in industrialized countries, it seems timely to extend transcatheter procedures to patients with non-calcified regurgitant aortic valves [14–17]. The few newer generation devices with dedicated anchoring systems improved the success rates [18] and highlighted how deployment requirements vary between AS and AR
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