The Technological Basis of a Balloon-Expandable TAVR System: Non-occlusive Deployment, Anchorage in the Absence of Calcification and Polymer Leaflets

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.

Polymeric prosthetic heart valves: A review of current technologies and future directions

“…The polymeric valve was tested in AWT at 15 Hz and reached the predetermined 400 million cycles. No signs of macro-degradation such as delamination of the free leaflet edge were seen as reported by the authors ( 23 ).…”

“…In vivo endothelialization of the PHVs has not been directly reported in the literature. The SAT valve, along with other PHVs, incorporates a degree of porosity in its electrospun skirt component ( 23 ). This porosity allows for capillary ingrowth across the thickness of the valve skirt, as seen in their bioprosthetic model ( 52 ).…”

“…Siloxane based polyurethane materials have also been used for PHV development. The SAT (Strait Access Technologies, South Africa) TAVR valve incorporates a PCU-based polymer, Carbosil 2080A TSiPCU ( Figure 2C ), which combines siloxane segments for biostability and carbonate segments for strength into a polyurethane base ( 23 ). Recently, a siloxane polyurethane-urea (LifePolymer, LP) was specifically developed for heart valve leaflets ( 24 ).…”

“…All samples were implanted into 5-week Long-Evans rats for 6 weeks. The authors report that the Carbosil material showed practically no calcification at all (0.28 ± 0.07 μg/mg), and significantly less as compared to even the decellularized tissue ( p < 0.05) ( 23 ). The biocompatibility of Carbosil had been previously shown in cage implants ( 47 ).…”

“…Studies have also shown greater thromboresistance compared to PTFE (20). 2C), which combines siloxane segments for biostability and carbonate segments for strength into a polyurethane base (23). Recently, a siloxane polyurethane-urea (LifePolymer, LP) was specifically developed for heart valve leaflets (24).…”