Alterations in collagen fiber crimp morphology with accelerated cyclic loading and transvalvular pressure fixation in porcine aortic valves

It is known that changes in the collagen fiber orientation of porcine bioprosthetic heart valves (PBHV) occur with (i) cyclic loading and (ii) fixation pressure. These changes correlate to alterations in biaxial extensibility, as reported by Wells et al. (2002). It is hypothesized that the increased collagen fiber alignment detected by small angle light scattering in (i) and (ii) is either due to the gross fiber splay, or a decrease in the colllagen fiber crimp (i.e. increase in crimp period). To address this hypothesis, we examined the changes in collagen fiber crimp morphology of PBHVs fixed at 0, 1, 2, and 4 mmHg transvalvular pressure, as well as 0 and 4 mmHg fixed PBHV following 0, 1×10⁶, 50×10⁶, 200×10⁶, and 500×10⁶ in vitro accelerated test cycles. Fast Fourier transform analysis of polarized light micrographs was used to calculate the collagen fiber crimp period. As PBHVs were fixed at increasing pressures, it was found that the crimp period increases from 15.2 μm at 0 mmHg to 21.4 μm at 4 mmHg. Additionally, a 65% increase in crimp period was observed between 0-50×10⁶ cycles in the 0 mmHg fixed valves, while only an 18% increase in the 4 mmHg fixed valves over the same cycle duration. We conclude that decreasing collagen crimp is a primary mechanism contributing to PBHV cyclic fatigue damage.