LONG-TERM EVALUATION OF ORTHOTOPICALLY IMPLANTED STENTLESS BIOPROSTHETIC AORTIC VALVES IN JUVENILE SHEEP

The aim of this study was to develop a technically feasible and reprod ucible model for chronic evaluation of stentless bioprosthetic aortic valves implanted orthotopically using juvenile domestic sheep. This re port summarizes the results of a study conducted to assess orthotopica lly placed 19-mm stentless aortic bioprosthetic valves. Twenty-seven j uvenile sheep underwent aortic valve replacement. Standard cardiopulmo nary bypass techniques were followed. The average cardiopulmonary bypa ss time was 73 min. No chronic anticoagulation was used. There were tw o deaths (7%) due to surgical complications. In the remaining 25 exper iments, 11 animals (41%) died prior to the scheduled sacrifice on post operative day 150. One early death occurred due to coccidiomycosis inf ection, one due to technical error, one due to pulmonary embolus, four due to prosthetic annular size disproportion, and four due to thrombi . The remaining 14 animals (52%) underwent left and right heart cathet erization, angiography, echocardiography, and sacrifice after postoper ative day 150. The average weight of the sheep at elective sacrifice w as 60 kg (mean weight gain 12.5 kg). The average cardiac output for th e sacrificed animals was 5.1 L/min. The mean velocity of blood across the aortic valve for the sacrificed animals was 317 cm/s and the mean pressure gradient was 26.2 mm Hg. Two features suggest that this model may have broad application. First, we have demonstrated that it is te chnically feasible to evaluate orthotopically placed stentless biopros thetic aortic valves in growing sheep. Second, the aortic root size of the juvenile sheep allows for implantation and evaluation of a human size aortic valve (19 mm). We believe that this model is reproducible and can be used to study stentless valve designs.