CHRONIC EVALUATION OF ORTHOTOPICALLY IMPLANTED BILEAFLET MECHANICAL AORTIC VALVES IN ADULT DOMESTIC SHEEP

This study was intended to develop a technically feasible and reproduc ible model for chronic hemodynamic and mechanical evaluation of orthot opically implanted bileaflet mechanical aortic valves in adult domesti c sheep. Three adult sheep (mean age 22 weeks, mean weight 76 kg) unde rwent aortic valve replacement using 19-mm bileaflet aortic valves. St andard cardiopulmonary bypass techniques were followed, including mild hemodilution, systemic hypothermia, and cardioplegic arrest. After pe rforming a left fourth intercostal thoracotomy, the valves were placed using interrupted 3-0 Ticron (Davis + Geck) inverted mattress sutures through a transverse aortotomy. The average cardiopulmonary bypass ti me was 58+/-1 min. No chronic anticoagulation was used. There were no surgical complications. All three animals (100%) remained clinically w ell until elective sacrifice after postoperative day 150. The average cardiac output for the animals at sacrifice was 3.8 +/- 1.0 L/min. The mean aortic ejection velocity was 304.7 +/- 47.3 cm/s and the mean pr essure gradient was 24.6 +/- 6.7 mm Hg. There was no clinically signif icant thrombus formation or paravalvular leaks. Thus, we have demonstr ated that it is technically feasible to orthotopically implant mechani cal aortic valves in sheep. There are several features that contribute to the success of this model, including use of a transverse aortotomy , adequate de-airing, and the use of mild hemodilution during bypass. We believe that this model is reproducible and can be used to study ot her valve designs. In addition, this model allows for site-specific pr eclinical assessment of new or modified mechanical heart valves.