Biaxial strain distributions in explanted porcine bioprosthetic valves

Testing whole explanted porcine bioprosthetic valves provides information on changes the valves undergo over time in vivo, and may help elucidate a possible mechanism for bioprosthetic valve failure. The study aim was to measure the static pressure/strain response of whole explanted porcine bioprostheses.

Three bioprosthetic valves were explanted prophylactically prior to structural failure. Loading curves (pressure versus strain curves) were generated for these valves using a whole-valve optical strain mapping system. Maximum strain, stiffness, and the occurrence of 'negative compliance' (inverse relationship between cusp strain and applied pressure) were obtained from these curves.

All three cusps had very low extensibility (3-10% in the radial direction; 2-4% in the circumferential direction). The non-coronary (NC) cusp was less extensible than the right (RC) or left coronary (LC) cusps in two of the valves. In one valve, the smallest strains were in the RC cusp, where large amounts of calcification were noted. Negative strains were present primarily in one valve.

The extensibilities of the three explanted valves were lower than those seen in fresh valves, due to either glutaraldehyde fixation and/or extension of the fibrosal corrugations. Furthermore, the uniqueness of the mechanical properties of the NC cusp previously seen in fresh porcine valves remained through glutaraldehyde fixation and stenting. It is concluded that cusp anisotropy and heterogeneity, as well as the occurrence of negative strains seen in fresh porcine valves, are preserved during the fabrication of porcine bioprostheses.