Effects of accelerated testing on porcine bioprosthetic heart valve fiber architecture.
We undertook the following study to quantitatively assess the changes in porcine bioprosthetic heart valve (PBHV) fiber architecture to increasing levels of fatigue damage using an in vitro accelerated test model. PBHVs were subjected to 0-500 million test cycles at 16 Hz, and small-angle light scattering (SALS) was used to quantify the gross fiber structure of the cusps. The degree of gross fiber alignment remained essentially constant from 0 to 500 million cycles over the entire cusp. Increasing fiber orientation randomness, indicative of local damage, was observed only in the vicinity of the nodulus of Arantii after 50 million cycles. The SALS data from the damaged regions suggested shearing between fiber layers, which may be part of the failure process and accelerates valve failure. Histological analysis revealed a relatively intact gross fiber structure with the collagen fiber crimp remaining, although delamination and de-registration of the crimp was also observed. Accelerated tested PBHVs also demonstrated a pronounced 'sagging', which began at the earliest cycle number tested (1.4 million cycles) and whose rate decreased logarithmically with cycle number. Results of this study suggest that PBHV cusps can alter their shape without any visually apparent material yielding or fiber failure under continual cyclic loading. Further, while most of the 4 mmHg pressure fixed PBHV's gross fiber architecture remains unchanged after 500 million cycles of accelerated testing, localized accumulated fiber damage can occur on a sub-visual structural level as early as 50 million cycles.