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

Figures

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  Figure 1. Size distribution of surgically implanted valves in a cohort of 350 patients with mainly rheumatic aortic regurgitation at Groote Schuur Hospital, University of Cape Town.

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  Figure 2. SAT balloon-expandable TAVR valve. The direct bonding to the MP35N-scallop allows an optimal attachment of polymer leaflets to the stent. Both the supra-annular anchorage arms and the spacer arms are structures that are self-elevating on the basis of plastic deformation. The first generation SAT TAVRs show minor differences between the bioprosthetic (A) and the polymer version (B). The second generation “universal” stent (C) supports both bioprosthetic and polymer leaflets and allows crimp-diameters for trans-femoral access.

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  Figure 3. Leaflet characteristics of SAT TAVR: normalized Von Mises stress of the PU (A) and BP (B) leaflets in the closed position shown as a contour plot of FEA results. Scanning electron micrographs of 100% pre-strained polyurethane leaflet films after 25 weeks of subcutaneous implantation in long-Evans rats demonstrating the degradation resistance of the SAT Carbosil leaflets (D) compared to significant surface degradation visible on the Pellethane control samples (C) (5,000×; Scale bar = 10 μm). While calcification (E) was distinctly reduced in the decellularized, sandwich-crosslinked bioprosthetic leaflets (D) both in bovine (−95%; left) and porcine (−97% right) pericardium compared to the control group (GA), Calcium levels were almost undetectable in the group of pre-strained Carbosil samples.

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  Figure 4. Fine-tuning of the thickness of the polymer leaflets in the pulse duplicator. With twice the cusp thickness on the left side (A,B) end-diastolic coaptation is identical (A,C) but endsystolic opening shows a more complete hinge-motion in the thinner leaflets (D) eliminating some areas with a potentially lower wash-out effect. The flaring of the top of the stent and the diameter increase is visibly compensated by the clam-shell design of the leaflets.

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  Figure 5. Crimping of a scalloped stent leads to distinct elongations of the skirt. Stretching is most pronounced along the indicated vectors (A) at the commissures; (B) at the infra-annular flare and (C) on the supra-annular arm.

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  Figure 6. Skirts are electrospun from the same material used for the polymer leaflets. Porosity was shown to allow transmural capillarization [bottom, from (17) with permission].

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  Figure 7. Outer dimensions of (M)-size pericardial (BP; n = 3) and polymer (PU; n = 3) SAT valves during expansion with a 26 mm non-occlusive SAT delivery device (n = 6). Measurements were taken at inflation increments of the balloon of 1 bar. (A) Overall shortening of the crimped valve during deployment. (B) A main feature of the SAT TAVR is that anchoring arms made of a non-shape memory alloy elevate on the basis of plastic deformation during expansion. The resulting diameter difference between waist and anchoring arms is already fully developed when the valve has only reached 60% of its maximum diameter. (C) With the supra-anular arms and the bottom flare having the biggest diameter difference to the “waist (nadir),” anchorage in compliant aortic roots is secured in both directions.

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  Figure 8. Profile view of the SAT TAVR stent relating key parts to the annular plain and showing the extent of arm-elevation achieved purely by the expansion force of the balloon. The average distance of the left coronary ostium (LCA) is shown in relation to the stent (*) (28–30).

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  Figure 9. Top view of a deployed SAT bioprosthetic (top) and polymer (bottom) TAVR showing the radius of the supra-annular anchoring-arms (red) vis a vis that at the waist level corresponding with the annular landing zone (blue). The schematic drawing (middle) shows that the supra-annular diameter is 25% bigger than the annular landing zone of the TAVR firmly securing anchorage (pull-out resistance >23 N) even in the absence of calcification. There is still ample space between the arms and the sinus wall in average sinuses of Valsalva.

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  Figure 10. The SAT non-occlusive balloon-delivery system consisting of a helical balloon is prevented from toppling by a Nitinol frame; (B) positioning- and stabilizer-trunks that are invaginating upon retraction; (A,C) a back-flow valve and (B) a pressurized rolling sleeve for device retrieval [(A) Reproduced from (31) with permission].

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  Figure 11. Radial force of the 26 mm non-occlusive delivery device for [M]-size TAVR. Three different inflation pressures were blotted against balloon-diameters (top): 8 bar (onset of non-occlusiveness); 14 and 18 bar (n = 3 × 3). In the pulse duplicator, effective orifice areas were determined against restricted balloon inflation (bottom).

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  Figure 12. SAT helical dilatation balloon. The helix is prevented from toppling by a fine-meshed Nitinol frame (C). A directional change at mid-level allows mirror-imaging of the proximal and distal ends (A). Profile of combined helical balloon and support frame (B). Dual inflation from both sides and relatively large feeding lines allow rapid inflation (C).