Parallel growth of rectus sheath grafts and recipient aorta. Critical role of graft tissue preservation.

Previous experimental studies revealed striking similarities in mechanical properties of host aortic tissue and rectus sheath inserted as an aortic graft, as well as enlargement of some of the grafts. We have now evaluated the capacity of rectus sheath grafts to keep pace with aortic growth and investigated the role of tissue preservation in determining the ability of such grafts to maintain suitable dimensions. Autologous rectus sheath grafts were substituted for thoracic aortic segments in 15 puppies, 8 weeks of age. Nine grafts were inserted with careful attention to tissue preservation (live grafts), but in six experiments, cells were killed and tissues fixed by freezing and thawing in acetone before graft implantation (devitalized grafts). Grafts were fixed in situ by controlled pressure perfusion and examined 1, 2, and 3 months after implantation. Over the 3 month experimental interval, body weight increased from 2.0 +/- 1 pounds to 25.0 +/- 2.5 pounds, and as is characteristic for the period of maximum growth rate for the animals. Total thoracic aortic length increased 41.2% +/- 6.1% and aortic diameter, 30.0% +/- 3.1%, during this time. Growth rate of the total thoracic aortic length during the first month was greater for the devitalized graft group, but aortic length was the same for both groups at 3 months. The live grafts increased 42.3% +/- 12.0% in length and 27.3% +/- 3.0% in diameter, i.e., to the same degree as the aorta, whereas the devitalized grafts showed only slight increases in length and diameter (2.1% +/- 2% and 5.3% +/- 5%, respectively). The live rectus sheath grafts were augmented and largely replaced by a newly formed, layered fibrocellular structure, 45.8 +/- 25.8 mm3 in volume, whereas in the devitalized grafts more of the original rectus sheath persisted and only a minimal amount of organized connective tissue sheath was formed (volume 18.7 +/- 8.9 mm3). In addition, cellularity was much greater in live grafts than in devitalized specimens (990.9 +/- 186.8 cells/mm2 and 423.6 +/- 124.7 cells/mm2, respectively). All of the grafts were lined by endothelium. These findings indicate that autologous rectus sheath aortic grafts may be used to provide channels which keep pace with aortic dimensions during the period of maximum growth, provided that the graft tissue is viable on implantation. Long-term durability of such grafts may also depend on tissue preservation.