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 (SAV) bioprostheses 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 standardized 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 = 1.5 mM) circulating at 37°C over 157.684 million cycles in a Hi-Cycle-tester to simulate 5 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.

Conclusions: 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.