The pathology of early failure in Mitroflow pericardial valve bioprosthesis (12A/LX)

Background Limited mid-term durability of 12A/LX Mitroflow bioprosthesis has been reported. Aim of the study was to ascertain the pathologic substrates and possible mechanisms of structural valve deterioration in explants from animals and humans. Methods Nine aortic 12A/LX Mitroflow bioprostheses preserved in hypotonic solution and three aortic 12A/LX bioprostheses, preserved in isotonic solution, were explanted from juvenile sheep, mean time from implant 95.66 ± 36.04 days and 132.33 ± 28.88 days from implant respectively. One stented unimplanted 12A/LX Mitroflow preserved in isotonic colution before glutaraldeyde fixation served as control. Ten aortic 12A/LX Mitroflow bioprostheses were explanted from humans because of severe dysfunction: five children, (3 females and 2 males, mean age 14.19 ± 4.77 years, range 11-21), 26 ± 8.24 months from implant and 5 adults (4 females and 1 male, mean age 57.4 ± 19.85 years, range 31-72), 64.4 ± 26.94 months from implant. X-ray, histology, and transmission electron microscopy were carried out as well as spectroscopy for calcium (Ca++) and phosphorus (P) content in human explants. Results Explants, from both animals and humans, showed cusp folding and stiffness, with coarse calcific deposits at gross examination and X-ray. Severe collagen denaturation, plasma insudation and massive calcification, involving both collagen and cell debris, were observed microscopically. Mean Ca++ content of 183.27 ± 62.48 and P content of 94.35 ±33.76 mg/g dry weight was found in children and Ca++ content of 205.49 ± 2.23 and P content of 99.75 ± 0.11 mg/g dry weight in adults. Obstructive fibrous tissue overgrowth was detected in 6 human cases. Conclusions Collagen denaturation was observed in pericardial Mitroflow 12A/LX bioprosthesis with premature structural valve deterioration. Optimal collagen fixation and preservation as well as phospholipids reduction by removing cell debris, as employed in the novel CROWN PRT Mitroflow bioprosthesis, are expected to solve the flaw and achieve long-term durability.