Current status of stentless aortic xenografts

The introduction of the Toronto stentless porcine valve (SPV) (St. Jude, Minneapolis, MN), recently approved by the Food and Drug Administration following a 6-year multi-institutional clinical trial from 1991 to 1997, reflects an evolutionary pursuit of an ideal valve substitute, namely, low thrombogenicity, freedom from anticoagulation, durability, easy availability, resistance to infection, and easy implantability. Currently, four different types of valve replacement have been time tested: mechanical valves, cryopreserved aortic homograft, stented heterograft, and pulmonary autograft (Ross procedure), and none of the available valve substitutes meet all the criteria of an ideal valve. The mechanical valve's favorable properties of durability and easy implantability are susceptible to thrombus formation, which requires lifelong anticoagulation. Although the aortic homografts are durable, with low incidence of infection and thrombogenicity, their widespread application has been limited by the lack of availability. The pulmonary autograft, with its native aortic valve properties, has been shunned by some surgeons because it requires a demanding technical expertise in implantation and needs an allograft in the pulmonary position. Stented xenografts are characterized by "off-the-shelf" availability, freedom from anticoagulation, easy implantability, and low incidence of infection. Its major drawback has been its limited durability. Another limitation is its residual transvalvular gradient. A modified version, a stentless xenograft, has been introduced to improve hemodynamic profiles in the hope of subsequent superior structural durability and patient survival. Two valves have been approved by the Food and Drug Administration, the Toronto SPV and the Freestyle valve (Medtronic, Minneapolis, MN). At The Methodist Hospital and the Baylor College of Medicine, the Toronto SPV stentless valve has been our stentless xenograft valve of choice. We therefore review the historical evolution, design advantages, surgical techniques, and clinical outcomes of this valve.