Ex-vivo characterization of three Björk-Shiley Delrin heart valves

Björk-Shiley Delrin (BSD) tilting-disc mechanical valve occluders have demonstrated good performance, with superior patient survival and low incidence of obstruction phenomena compared to caged-ball valves. Unfortunately, the use of Delrin as the occluder material was problematic, and in 1971 this led to its replacement with a pyrolitic carbon-coated occluder. The study aim was to report and to determine the mechanism of wear on BSD valve discs. To achieve this, three BSD valves which had been in place for between 312 and 355 months were explanted and analyzed.

Optical microscopy and scanning electron microscopy were used to investigate material imperfections or damage to the housing and occluder components of the explanted valves.

The valve discs showed more than one type of wear pattern. Notably, the wear pattern observed on the surface and edge of the disc did not affect correct in-vivo function of the valves, as indicated by their long implantation period. No cracks, fractures or perforations of the Delrin discs were observed, but clear imprints caused by the impact of the struts on the inlet and outlet disc surfaces were detected. The depth of the strut imprints was indicative of a hindered disc rotation. A reduction in the diameter of the Delrin disc (ca. 1.44 mm) was detected in valve #3.

The results obtained for the three BSD valves were in agreement with data reported elsewhere, and showed good performance of this mechanical valve. Although the clinical follow up for these second-generation mechanical valves is extensive and supportive of their good clinical performance, they may in time fail due to wear of the polymer surface.