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Pathology of Structural Valve Deterioration in Cryolife O' Brien Porcine Stentless Aortic Prostheses

Cristina Basso1, Fabio Ius1, Mila Della Barbera1, Marialuisa Valente1, Ugolino Livi2, Gaetano Thiene1.
1University of Padua, Padova, Italy, 2Azienda Ospedaliera Universitaria, Udine, Italy.

BACKGROUND- Although early and mid-term haemodynamic and clinical results of Cryolife O’Brien (CLOB) stentless valves are favourable with less gradient and regression of left ventricular hypertrophy, long term durability is limited. Pathological studies of explanted CLOB prostheses have never been reported.
METHODS- Nine CLOB stentless aortic prostheses (size 21 mm in 5, 25 mm in two and 27 mm in two), explanted at reoperation from 5 male and 4 female patients, underwent pathological investigation. Native valve dysfunction was stenosis or steno-incompetence in 7 (4 with bicuspid and 3 with tricuspid aortic valve) and incompetence due to infective endocarditis in two. Mean age at implant 62±15 years (range 25-76), mean implant duration 121 ± 29 months (range 57-150). Reason for valve reoperation was severe incompetence in all. The study protocol consisted of gross examination, photography with a stereoscope, and X-Ray for semiquantitative analysis of Ca2+deposits (0 to 4 score) and atomic absorption spectroscopy (AAS) analysis of calcium (Ca) and phosphorus (P) content (mg/g dry weight). Histopathologic study with haematoxylin-eosin, Heidenhain-trichrome, elastic-van-Gieson and Von-Kossa stains was performed.
RESULTS- At gross and X-Ray, calcification was massive (4+) in one, severe in 2 (3+) and moderate (2+) in 6, involving in all the commissures. Cusp commissural and belly tearing was observed in all explants, related at histology to calcium depositions and to lipid insudation, with cholesterol clefts, lipid-laden macrophages (foam cells) and giant-cell foreign-body reaction. Dissecting hematoma of a cups was additionally observed in one case. The mean Ca and P content at AAS was 50.58 ± 64.73 mg/g dry weight (range 3.33-174.41) and 30.14 ± 32.84 mg/g dry weight (range 6.20-99.52), respectively.
CONCLUSIONS- Dystrophic calcification and lipid insudation with commissural tearing represent the main causes of structural valve deterioration jeopardizing the long-term durability of CLOB stentless aortic prostheses. These features are quite similar to those observed in stented porcine prostheses, indicating that anticalcification strategies and serum lipid control should be pursued to increase durability of porcine valve xenografts.
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