Influence of fixation conditions on the performance of glutaraldehyde-treated porcine aortic valves: towards a more scientific basis.

Abstract

To maintain optimum mechanical properties in glutaraldehyde-treated heart-valve tissue the full collagen crimp geometry originally present in the relaxed fresh tissue should be retained. By varying the pressure at which glutaraldehyde fixation is carried out, considerable alterations to this crimp geometry can be achieved. The mechanical stiffness of the preserved tissue is consequently affected, and this in turn has a striking influence on both the opening behaviour of the valve and the degree of strain localisation in the leaflet tissue.A pressure of 100 mmHg eliminated the collagen crimp geometry entirely, and this resulted in the formation of sites of local strain or kinks in the valve leaflets during opening. It is expected that this strain localisation phenomenon will influence the long-term fatigue durability of the treated tissue. Pressures even as low as 4 mmHg result in significant reductions of crimp geometry.Fresh valves should therefore be fixed under a positive head of pressure sufficient only to ensure that the leaflets seal along their coapting free margins. A pressure of less than 1 mmHg was sufficient to achieve this.Leaflets of the commercially available Hancock valve show features similar to valves fixed in glutaraldehyde at about 100 mmHg pressure.

Bioprosthetic Heart Valves: Impact of Implantation on Biomaterials

“…The concentration of glutaraldehyde used has gradually been decreased to 0.2% v/v, in an effort to reduce these changes, without compromising quality. [8] reported that fixation of BHV under high pressure (80 mmHg) distorts the crimp geometry of collagen and causes early matrix fragmentation, stiffening and kinks in the valve leaflets during opening, and early valve deterioration. Some prostheses are now fixed at physiological pressures (under 4 mm Hg) in an effort to minimize this effect.…”

The aortic valve microstructure: Effects of transvalvular pressure

“…Later it became known that high pressure fixation was responsible for an increase in the cusp's bending stiffness, which was presumed to cause buckling when the cusp is forced to take on high curvatures. In particular, using high speed film Broom and Thompson 10 determined that high pressure fixation induced kinks in the cusps, which also were locations of noticeable fatigue damage of the fiber network. Contemporary PBHVs are fixed at low transvalvular pressures, generally between 0 and 4 mmHg, which is thought to benefit mechanical durability by maintaining collagen fiber crimp structure.…”

Tissue Heart Valve Replacement at BSMMU- Initial Experience with Two Cases

“…Second-generation tissue valves (that are glutaraldehyde fixed under low pressure) are considered more durable than first-generation tissue valves (that are glutaraldehyde fixed under high pressure) 8 .…”