Durability testing with calcification of surgical aortic valves and transcatheter heart valves: An in-vitro study

Objectives Structural valve deterioration, mainly caused by calcification, is the Achilles heel of the bioprosthetic-heart- valves. While clinical long-term experience of surgical aortic valve bioprostheses (SAV) exists, transcatheter heart valve (THV) requires further investigations into biological degeneration. Therefore, this in-vitro study aimed to analyse the calcification pattern of different SAV and THV-models under standardised conditions. Methods SAVs (Perimount Magna Ease, Perimount, Mosaic Ultra and Hancock II) and THVs (Evolut PRO and SAPIEN XT) models were calcified with a calcification-buffer (pH = 7.4 and CaCl2=1.5mM) circulating at 37 °C over 157.684 million cycles in a Hi-Cycle-tester to simulate five patient-years. Hydrodynamic performance (mean pressure gradient (MPG) and effective orifice area (EOA)) of the valves were compared in a pulse duplicator before and after calcification. The calcified-group and one untreated prosthesis (control-group) were analysed by macroscopic-evaluation, tissue-thickness-measurement, calcium-titration, scanning-electron-microscopy, and histological-examination (n = 12). Results After durability testing, the MPG and EOA of all valves changed significantly, except for Evolut PRO. The valve leaflets of the calcified-group presented hydroxyapatite-crystals and a distinct calcification along regions with high mechanical stress—the commissures, nadirs, and ventricle side. Durability testing with calcification-buffer resulted in significantly higher calcium-content within all valve models' leaflets than in their control-group. The THVs showed superiority vs surgical valves regarding the susceptibility to calcification, with a degree of calcification differing significantly depending on the valve model. Conclusion The Evolut PRO THV's functional performance was not significantly impaired after durability testing. Further clinical evaluation of this aspect is essential to confirm the susceptibility to calcification of bioprosthetic-heart-valves.