THE EVOLUTION OF PROSTHETIC VALVE DESIGN

The first surgical heart valve replacement was undertaken over half a century ago since when there has been a continuing quest to develop a prosthesis with the perfect combination of durability, haem-atological compatibility and haemo-dynamic performance. Early caged ball mechanical valves were robust but asso-ciated with red cell trauma and rapidly fol-lowed by introduction of mono-leaflet and bi-leaflet designs which remain in use today. Introduced later in the 1960s, bio-prosthetic valves consisting of pericardial or valve tissue mounted on a frame and sewing ring were initially conceived for use in elderly patients unlikely to outlive the valve, or in other patients at risk of bleeding complications associated with anticoagulation. Until recently, mechanical valves have remained the logical choice in patients <65 years of age given the minimal rates of primary valve failure.1 However, advances in the longevity and haemodynamic performance of modern bioprostheses and the emerging potential for transcatheter treatment when they degenerate seem set to challenge this paradigm.2 Stentless bioprosthetic valves offer the potential for (A) further improvements in the flow dynamics of cardiac output and consequent haemodynamic performance, (B) remodelling and dynamic adaptation to the anatomy of the aortic root with resulting progressive increase in the effect-ive orifice area, and (C) enhanced regres-sion of left ventricular hypertrophy with improved clinical outcomes. Although initial comparative studies demonstrated superior haemodynamics, prospective randomised controlled trials against modern stented bioprosthetic valves with lower profile frames, thinner sewing rings and excellent haemodynamic characteris-tics3 have shown no major differences in clinical and echocardiographic endpoints at 1-year follow up.