HIGH-RESOLUTION MAGNETIC-RESONANCE-IMAGING TO CHARACTERIZE THE GEOMETRY OF FATIGUED PORCINE BIOPROSTHETIC HEART-VALVES

Background and aims of the study: Porcine bioprosthetic heart valves ( PBHV) continue to suffer from limited long-term durability. Failure of PBHV occurs mainly in the cusps and is characterized by mechanical da mage, usually in conjunction with calcification, Mechanisms underlying calcification have received considerable attention, yet mechanical da mage phenomena remain poorly understood, The structural response of PB HV cusps to in-vivo cyclic loading involves three primary factors: (i) mechanical properties; (ii) fiber architecture; and (iii) 3D geometry , Previous finite element studies have shown cuspal stress distributio n to be highly sensitive to subtle changes in geometry, yet to date, c usp geometry has been largely ignored in studies of PBHV durability. M ethods: A non-destructive method was developed to quantify PBHV 3D geo metry using high-resolution magnetic resonance (MR) imaging, Images we re obtained in three orthogonal planes from virgin and accelerated tes ted (50 x 10(6) and 200 x 10(6) cycles) PBHVs to fully capture 3D cusp al geometry. Surface curvatures were computed using a local biquadric surface patch approach. Results: Results indicated a tendency for cusp s to permanently deform with accelerated testing, manifesting primaril y as sagging of the cusp. This sagging induced areas of high curvature from the central belly region upwards to the nodulus of Aranti, corre sponding to known locations of tissue failure. Conclusions: at is like ly that the observed changes in cuspal geometry induce deleterious alt erations in the stress distribution, independent of those related to m echanical properties and fiber structure, and contribute tea valve fai lure. Our results suggest that PBHV designers should attempt to compen sate for the deleterious geometric changes that occur post-implantatio n.