Radiographic assessment of leaflet motion of Gore-Tex laminate trileaflet valves and Hancock xenograft in tricuspid position of dogs

Immobile Leaflets at Time of Bioprosthetic Valve Implantation: A Novel Risk Factor for Early Bioprosthetic Failure: A Novel Risk Factor for Early Bioprosthetic Failure

OBJECTIVES

The clinical implications of finding immobile leaflet(s) at the time of bioprosthetic valve implantation but with acceptable prosthetic haemodynamics are uncertain. We sought to determine the characteristics of such patients and their impact on outcome.

METHODS

Patients with immobile leaflet at the time of surgical bioprosthetic valve implantation were identified retrospectively by a systematic search of an institutional echocardiography database (2010-2020). Intraoperative echocardiograms were reviewed de-novo to confirm immobile leaflet(s) at the time of implantation. Cases were matched 1:2 to controls with normal bioprosthetic leaflets motion for age, sex, prosthesis position, prosthesis model, size, year of implantation, and pre-implantation left ventricular ejection fraction. Proportional hazards method was used to analyse the composite endpoint of stroke, valve thrombosis or re-intervention.

RESULTS

Immobile leaflet at the time of bioprosthetic valve implantation were found in 26 patients (median age 71 ys 39% males) following tricuspid (n=13), mitral (n=11) and aortic (n=2) valve replacements; 96% received porcine prostheses; prosthesis size was 27 mm or larger in 92%. Immobile leaflet were recorded on intraoperative reports in 16 (62%) cases. It resulted in elevated gradient or mild-moderate prosthetic regurgitation in three (12%), but none led to immediate corrective action intraoperatively. At median follow-up of 21 (4-50) months, presence of immobile leaflet was associated with composite clinical endpoint of stroke, valve thrombosis or re-intervention (hazard ratio 6.8 95% CI 1.8-25.2 p<0.01) compared to controls.

CONCLUSION

Immobile leaflet immediately post-bioprosthetic valve implantation is frequently under-recognised intraoperatively and appears to be associated with early bioprosthetic dysfunction and worse clinical outcome.

Mechanical considerations for polymeric heart valve development: Biomechanics, materials, design and manufacturing

The native human heart valve leaflet contains a layered microstructure comprising a hierarchical arrangement of collagen, elastin, proteoglycans and various cell types. Here, we review the various experimental methods that have been employed to probe this intricate microstructure and which attempt to elucidate the mechanisms that govern the leaflet's mechanical properties. These methods include uniaxial, biaxial, and flexural tests, coupled with microstructural characterization techniques such as small angle X-ray scattering (SAXS), small angle light scattering (SALS), and polarized light microscopy. These experiments have revealed complex elastic and viscoelastic mechanisms that are highly directional and dependent upon loading conditions and biochemistry. Of all engineering materials, polymers and polymer-based composites are best able to mimic the tissue-level mechanical behavior of the native leaflet. This similarity to native tissue permits the fabrication of polymeric valves with physiological flow patterns, reducing the risk of thrombosis compared to mechanical valves and in some cases surpassing the in vivo durability of bioprosthetic valves. Earlier work on polymeric valves simply assumed the mechanical properties of the polymer material to be linear elastic, while more recent studies have considered the full hyperelastic stress-strain response. These material models have been incorporated into computational models for the optimization of valve geometry, with the goal of minimizing internal stresses and improving durability. The latter portion of this review recounts these developments in polymeric heart valves, with a focus on mechanical testing of polymers, valve geometry, and manufacturing methods.

Polymeric heart valves: new materials, emerging hopes

Heart valve (HV) replacements are among the most widely used cardiovascular devices and are in rising demand. Currently, clinically available devices are restricted to slightly modified mechanical and bioprosthetic valves. Polymeric HVs could represent an attractive alternative to the existing prostheses, merging the superior durability of mechanical valves and the enhanced haemodynamic function of bioprosthetic valves. After early unsatisfactory clinical results, polymeric HVs did not reach commercialization, mainly owing to their limited durability. Recent advances in polymers, nanomaterials and surface modification techniques together with the emergence of novel biomaterials have resulted in improved biocompatibility and biostability. Advances in HV design and fabrication methods could also lead to polymeric HVs that are suitable for long-lasting implantation. Considering all these progresses, it is likely that the new generation of polymeric HVs will find successful long-term clinical applications in future.