Heart valve bioprosthesis durability: a challenge to the new generation of porcine valves.
Long-term experience with first generation porcine valve xenografts enabled identification of the major limitations to their durability: (1) prosthetic-ventricular mismatch due to the high profile of the stent in patients with mitral stenosis and a small left ventricle; (2) high-pressure fixation with loss of natural collagen crimping in the fibrosa, and wash-out of proteoglycans in the spongiosa; (3) xenograft tissue autolysis, due to the long interval between animal slaughter and aortic valve removal fixation; (4) muscle shelf in the right coronary cusp, which created a gradient and could undergo accelerated calcification and/or spontaneous perforation with time; (5) a flexible polypropylene stent, which could creep or even fracture with consequent inward bending of the stent; (6) progressive time-related dystrophic calcification; (7) host fibrous tissue ingrowth. An awareness of these limitations stimulated technical modifications, which frequently brought about distinct improvements: (1) the reduction of the stent profile eliminated the problem of mismatch, but resulted in a higher tendency towards cusp prolapse and earlier commissural tearing; (2) natural collagen waviness, proteoglycans and cusp extensibility were preserved by employing low or even zero pressure during the fixation process; (3) earlier valve fixation enabled preservation of cell integrity; (4) a new orifice for small valves was designed by replacing the right muscular cusp, thus achieving less gradient and avoiding muscle-shelf-related complications; (5) polypropylene was replaced by Delrin as stent material; (6) calcium-retarding agents like T6 and toluidine blue were applied during commercial processing and storage in order to mitigate tissue mineralization.(ABSTRACT TRUNCATED AT 250 WORDS)
Valente
M
M
Department of Pathology, University of Padova Medical School, Italy.
Minarini
M
M
Maizza
A F
AF
Bortolotti
U
U
Thiene
G
G
D001705:Bioprosthesis / Q000145:classification / Q000592:standards* / Q000639:trends; D002114:Calcinosis / Q000453:epidemiology / Q000209:etiology; D006350:Heart Valve Prosthesis / Q000145:classification / Q000592:standards* / Q000639:trends; D006801:Humans; D011474:Prosthesis Design / Q000592:standards; D011475:Prosthesis Failure; D011786:Quality Control; D015607:Stents / Q000592:standards; D014021:Tissue Preservation / Q000379:methods / Q000592:standards