Seminars in thoracic and cardiovascular surgery vol:11 issue:4 Suppl 1 pages:163-70
Stent mounting of xenografts induces a loss of mobility and reduces the effective valve orifice. By contrast, the higher surgical technical expertise required for stentless procedures is a major obstacle for many surgeons. To facilitate the insertion of the Toronto SPV (St Jude Medical Inc, St Paul, Minneapolis, MN) stentless aortic valve, we tried to alter the porcine design by lowering the invasive profile at the depth of the sinuses on both coronary sites. This technique could theoretically facilitate implantation of the modified stentless valve with an easygoing single-layer suture at the challenging subcoronary level and make it more attractive for the surgeon. The standard model was modified by lowering the profile at the depth of the sinuses on both coronary sites, whether by plication (in 3 specimens, one of each size) or excision (in 3 others) of the protruding porcine aortic wall at the nadir of each coronary sinus. Animal implants in juvenile sheep (6 standard Toronto versus 6 modified valves of 21, 23, and 25 mm) were studied for durability and biocompatibility for 3 to 6 months. All valves were evaluated by postoperative echocardiography and after explantation examined macroscopically, radiographically, histologically, and electron microscopically. The standard valves performed well, although at 6 months after implantation, marked fibrosis was found at the outflow parts with scattered calcifications, essentially in the porcine aortic wall. The leaflets remained mobile and contained scant mineralization. By contrast, the modified specimen showed markedly accelerated fibrosis and significant cusp calcifications at distance from the altered zones. Severe restriction of the mobility of the leaflets was visible 3 months after implantation in the juvenile sheep model. The more pronounced the deformation of the modified scaffold, the faster and more intense the degradation and calcification of the leaflets far from the altered zones (worse in the heavily deformed, plicated cusps). Because all valve types were prepared by identical preservation techniques, this study shows that loss of mobility by distortion of the natural scaffold induces early failure. It is extremely important to correct implantation of stentless valves to prevent early degeneration.