Characteristic calcification behavior of five surgical aortic valve bioprostheses models: An in vitro study

The durability of surgical aortic valve bioprostheses (SAV) is limited by the calcification of the leaflets, which results in degeneration. In clinical routine, there seems to be substantial variability in the degeneration of specific SAV models. Our study aims to establish an in vitro calcification model for prosthetic valves, characterizing the calcification behavior of different SAVs.

Five commercially available SAV models (Epic™ Supra, Freestyle®, Intuity®, Perimount®, and Trifecta™) were perfused with double-distilled water and physiological buffer with a defined calcium concentration (CaCl₂ = 1.5 mM) at 37°C over 32.9 million cycles in a Hi-Cycle tester which corresponds to approximately 1 patient-year (calcified group). Untreated prosthetic valves served as the negative control group (noncalcified group). Calcium titration, scanning electron microscopy (SEM), histological examination, and tissue thickness measurements were performed to evaluate noncalcified and calcified SAVs (n = 10).

Treatment in the Hi-Cycle tester with calcification buffer maintained significantly higher calcium absorption of SAVs compared to the control group (p < 0.001). Additionally, hydroxyapatite crystals were found in the calcified SAV in SEM. Porcine valves rarely demonstrated punctual calcification pattern, while bovine pericardial valves presented distinct planar calcification pattern in histological examination. Further, calcification content differed significantly depending on the SAV model, with the highest calcium content in Trifecta (213 µg/cm²) and the lowest in Epic Supra (8 µg/cm²) (p < 0.001).

Data from our study revealed significant differences in leaflet calcification for the various aortic valve bioprostheses models. Further studies are necessary to investigate whether these findings can mimic the clinical data of the implanted prostheses.