In Vitro Investigation of Calcification of Five Surgical Aortic Valve Bioprosthesis Models

Background: The durability of aortic valve bioprostheses (AVBP) is limited by calcification of the leaflets resulting in degeneration and in clinical routine there seems to be a substantial variability in degeneration of specific AVBP models. Our study aims to establish an in vitro calcification model for prosthetic valves characterizing the calcification behavior of different surgical AVBPs.

Method: Five commercially available surgical AVBP models (Epic supra, Freestyle, Perimount, Intuity, Trifecta GT) were perfused with double-distilled water and physiological buffer with a defined calcium concentration (pH = 7.4; KCl = 55 mM, CaCl² = 1.5 mM, KH2PO4 = 1.25 mM, Na2HPO4 = 0.32 mM, NaH2PO4 = 0.11 mM) at 37°C over 32.9 million cycles in a Hi-Cycler which corresponds to ~1 patient-year (calcified group). Untreated prosthetic valves served as the negative control group (noncalcified group). Calcium titration, electron microscopy (EM), histological examination, and transmission light absorption method (TLAM) were performed to evaluate noncalcified and calcified AVBP (n = 10). Mean pressure gradient and effective orifice area were measured in a heart simulator before and after calcification.

Results: Histological examination and TLAM demonstrated calcification after Hi-Cycler procedure, while no calcification was found in the noncalcified group. The calcifications were mostly located at the commissures and nadirs. EM presented hydroxyapatite crystals in the calcified AVBP. Calcium titration showed significant differences of calcium content between calcified versus noncalcified AVBP (Table 1). Calcification values differed significantly depending on the AVBP model (p < 0.001). The highest calcification content (calcium value in µg per cm² valve area) was found in Trifecta and the lowest in Epic ([Table 1]).

Table 1

Prosthesis	Calcified (Ca µg/cm2)	Noncalcified (Ca µg/cm2)	p-Value
Epic supra	8.2 ± 2	3.2 ± 0.2	< 0.001
Freestyle	17.2 ± 0.1	3.1 ± 0.3	< 0.001
Intuity	131.9 ± 1.7	3.5 ± 0.1	< 0.001
Perimount	179 ± 2	3.2 ± 0.2	< 0.001
TrifectaGT	211.1 ± 5.2	3.2 ± 0.2	< 0.001

Conclusion: Data of 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.

Publication History

Article published online:
03 February 2022