TAVR Valve Alloy Composition
TAVR valves utilize two primary alloy types depending on the valve platform: balloon-expandable valves use cobalt-chromium alloy, while self-expanding valves use nitinol (nickel-titanium alloy).
Balloon-Expandable Valves: Cobalt-Chromium Alloy
The Edwards Sapien family of balloon-expandable TAVR valves employs a cobalt-chromium alloy frame that provides the structural support for the bioprosthetic leaflets 1. This alloy composition offers several key advantages:
- High radial strength that allows the valve to maintain its position and resist compression after deployment 2
- Superior radiopacity for enhanced fluoroscopic visualization during implantation 2
- Tubular slotted design that creates a cylindrical, relatively short stent structure 1
Specific cobalt-chromium variants include nickel-cobalt-chromium MP35N alloy, which has been utilized in newer TAVR designs for its enhanced mechanical properties 3.
Self-Expanding Valves: Nitinol Alloy
The Medtronic CoreValve family of self-expanding TAVR valves utilizes a nitinol (nickel-titanium) alloy frame 1. Nitinol's unique properties make it ideal for self-expanding valve platforms:
- Shape memory characteristics allow the frame to expand to its original shape once unsheathed and heated to body temperature 2
- Adaptive shape design that creates a taller stent with supra-annular positioning 1
- Flexibility that accommodates varying anatomical configurations while maintaining structural integrity 2
Clinical Implications of Alloy Selection
The choice between cobalt-chromium and nitinol alloys directly impacts procedural technique and patient selection:
- Cobalt-chromium (balloon-expandable) valves require balloon inflation for deployment, providing precise control but necessitating rapid ventricular pacing during deployment 1
- Nitinol (self-expanding) valves deploy gradually without rapid pacing, and newer generations (CoreValve Evolut R) can be recaptured and repositioned before full deployment 1
Additional Structural Components
Beyond the primary alloy frame, TAVR devices incorporate:
- Polyethylene terephthalate fabric or pericardial skirts on the lower frame portion to reduce paravalvular leakage 2
- Bioprosthetic tissue leaflets (bovine or porcine pericardium) mounted on the alloy frame, not the frame itself being the functional valve component 1
The alloy frame serves purely as the structural scaffold, while the actual valve function comes from the attached bioprosthetic tissue 4.