Failure of porcine aortic and bovine pericardial prosthetic valves: an experimental investigation in young sheep.

Seventeen porcine aortic and 10 bovine pericardial bioprosthetic valves were implanted in the tricuspid position in 27 young sheep. Clinical, hemodynamic and morphologic evaluations were performed after a mean of 4.7 +/- 0.3 months (range 3-7 months) after implantation. Eight sheep developed ascites (five with porcine aortic and three with bovine pericardial bioprosthetic valves); all 27 sheep had microscopic evidence of hepatic congestion. Three porcine and three bovine valves became infected. Hemodynamic studies (n = 15) performed immediately after implantation and at the time of terminal elective studies showed that tricuspid valve end-diastolic gradients increased from 0.7 +/- 0.4 mm Hg to 4.5 +/- 0.5 mm Hg (p less than 0.01). All 27 valves had calcific deposits. By quantitative analyses, unimplanted cuspal tissue (n = 9) had 0.6 +/- 0.1 mg/g of calcium/g tissue dry weight; explanted porcine aortic valves (n = 16) had 182 +/- 74 and bovine pericardial valves (n = 6) 421 +/- 115 mg/g of calcium/g of tissue dry weight (NS for porcine aortic vs bovine pericardial valves). Morphologic findings were similar in both porcine aortic and bovine pericardial valves, and consisted of calcific deposits, collagen degeneration, microthrombi and fibrous sheaths. These findings are almost identical to those associated with bioprosthetic valvular failure in humans. In our experimental study, we found no significant differences in the development of calcification in porcine aortic and bovine pericardial bioprosthetic valves.