For a given external diameter, the internal diameter of the stentless valve is 2 to 4 mm larger than a stent mounted xenograft valve due to lack of a stent. This translates to an ability to place a bioprosthesis with a greater effective orifice area and reduce mean transvalvular gradients. An increased understanding of the functional anatomy of the aortic root has reinforced the concept of the dynamic relationships among the valve cusps, annulus, sinus of Valsalva, and sinotubular junction. The use of a stentless valve maintains these interactions resulting in improved hemodynamic performance. Recent studies show that the use of stentless xenograft valves has resulted in lower mean transvalvular gradients and a greater reduction in left ventricular mass than stented valves.
Early data shows a trend towards improved long term survival in stentless valves.
Implantation of a stentless xenograft aortic valve is technically more difficult than a stented valve but easier than an allograft used in the subcoronary position. The Toronto SPV is comprised of the valve and supporting aortic wall only, and is designed as a subcoronary implant. The Freestyle valve is a root xenograft that may be used for either a subcoronary, cylindrical or a root replacement implant. A technique for the subcoronary implantation technique of the Toronto SPV is described. Incision A full median sternotomy or upper hemisternotomy may be used.