Disproportionate enlargement of the pulmonary autograft in the aortic position in the growing pig

Purpose: This study was aimed to demonstrate growth in the pulmonary autograft after transplantation to the aortic position. Methods and materials: In 20 piglets (weight 25.4 ± 3.5 kg) (mean ± standard deviation) a Ross operation was performed and in five piglets (weight 9.3 ± 0.7 kg) (mean ± standard deviation) the ascending aorta was replaced with a valveless pulmonary autograft. Animals were allowed to grow as much as possible. Postmortem explanted autografts were studied by direct measurements of the valve cusps in the Ross group and of the wall segments in the valveless autograft group. Measurements of the first group were compared with the values of a separate control group, and values of the second group were compared with values of samples taken at operation. Results: In the Ross group, cuspal weight, height, and width increased significantly by comparison with body weight (p ≤ 0.003). The rate of increase did not differ significantly from that of the control group with a native pulmonary valve. However, there was a rapid adaptation of the autograft valves resulting in a significantly higher mean cuspal weight, height, and width. In the valveless autograft group, wall circumference, thickness, and height increased significantly (p ≤ 0.001). The circumference increased significantly more than that of the native pulmonary wall. Compared with the native aortic wall, the pulmonary autograft media showed retained pulmonary architecture on microscopic study. Conclusion: These data suggest that the dimensional increase of the pulmonary autograft in the aortic position in the growing pig is determined by growth and dilatation, that the valve mass increases more than that of the native pulmonary valve, and that the characteristic pulmonary microscopic architecture is retained.