The history of stentless xenograft aortic valves follows in the footsteps of the aortic homograft, which was considered historically as the best biologic prosthesis for management of root pathology and for optimizing hemodynamics in the absence of root pathology. The original concept behind creating a stentless xenograft valve was to maintain the excellent hemodynamics of the homograft, while improving on the availability, durability, technical complexity, and costs associated with homografts.
Stentless, or "natural valve" substitutes closely mimic the native aortic root anatomy and are implanted without a stent, large sewing ring, or other supporting apparatus that can lead to persistent LV obstruction sometimes observed with stented bioprostheses or mechanical valves. In general, use of stentless valves also allows for implantation of larger prostheses with resultant larger effective orifice area for any given LV outflow tract diameter. Comparing homografts, autografts and xenografts, stentless porcine constructs have the most opportunity for wide-spread application because of their ready shelf availability and ease of implantation. Compared with traditional stented bioprostheses, touted advantages of stentless valves include better hemodynamics,1-3 improved regression of left ventricular mass,3-5 less risk of patient-prosthesis mismatch (ppm) in the small aortic root,6 and possibly improved long-term survival.7,8 Because of these advantages, over the past 15 years, aortic valve replacement (AVR) with stentless porcine bioprostheses has become an accepted technique for routine treatment of aortic valve and root diseases. Some of these advantages appear to be maximized with implantation using a total root replacement technique, which also is associated with less risk of late valve failure.9 However, the potential benefits of stentless valves implanted as total roots may come at the cost of increased operative risks, including a potential for higher operative mortality compared with subcoronary stentless or stented AVR.9 Although other large series have reported low operative mortality with stentless root replacement,10-12 a learning curve of over 20 cases has been described.13 Besides a learning curve for this more complex procedure, other factors that could potentially contribute to excess mortality include longer perfusion and myocardial ischemic times, and more suture lines exposed to the pericardial space. Thus, the use of stentless aortic bioprostheses has become a controversial topic within the cardiothoracic surgical community.
Many stentless xenograft valves have come and gone in the marketplace over the past decade. Currently, the only two stentless prostheses available are the Medtronic Freestyle bioprosthesis and the ATS 3F valve, which has only recently been introduced to the North American market.
The Medtronic Freestyle valve followed closely behind the development of the St Jude Toronto SPV, which is now out of production. From its beginning, the Freestyle valve had several options of implantation techniques, similar to the homograft, including full root, root inclusion, and subcoronary positions. The Freestyle valve began clinical application in the early 1990s, thus making some long-term outcome data available. The Freestyle is a ...