Growth of fresh-frozen pulmonary allograft conduit in growing lambs

To investigate the fate of cryopreserved pulmonary conduit allografts, an experimental model was used in lambs. The lambs underwent resection of the pulmonary trunk and valve to the level of the bifurcation of pulmonary arteries and then were replaced by cryopreserved (CryoLife, Incorporated, Laboratories) pulmonary conduit allografts obtained from lambs of similar size. Lambs were operated on at 4 weeks of age and followed up with cardiac catheterization and cineangiography every 3 months for a period of 18 months. Lambs were electively sacrificed in the following order: two at 1 month, two at 3 months, one at 6 months, two at 12 months, and five at 18 months. To assess the structure of the conduit tissue, sections for light microscopy were obtained from the proximal, midportion, and distal ends of the conduit. While the lambs grew from a weight of 11.7 kg at the time of implant to more than 70 kg at 18 months, the diameter of the pulmonary conduit distended from 16 mm at the time of implant to 17.7, 19.1, 24.9, 34.3, and 33.7 mm at 1, 3, 6, 12, and 18 months, respectively. The length of the conduit extended from an original inner length of 25 mm and an original outer length of 32 mm to the following dimensions: inner lengths of 27.9, 32.7, 38.8, 43.6, and 45.3 mm, respectively, at 1, 3, 6, 12, and 18 months. The outer lengths changed to 47.4, 52.4, 56.2, 71.4, and 69.0 mm, respectively, at 1, 3, 6, 12, and 18 months. The valve of the conduit remained competent, and pressure gradient across the proximal anastomosis remained steady at 27 mm Hg. Microscopic examination showed that although the elastic tissue is fairly well preserved by the CryoLife, Incorporated, preservation method, the tissue remained acellular and nonviable. Multifocal, mild calcification of the conduit occurred after 3 months.