Quantitative Analyses of Vitrified Autologous Venous Arterial Bypass Graft Explants

The purpose of this study was to compare vitrified small diameter venous arterial bypass graft explants with fresh graft controls using quantitative morphometrics and smooth muscle physiology. Fresh and vitrified reversed ipsilateral external jugular veins were used as autologous common carotid interposition bypass grafts on the right side in New Zealand White rabbits. Animals were sacrificed at either 2 or 4 weeks after implantation, and the vein grafts were harvested for study. Histology revealed that the vitrified grafts initially arteriolized more slowly than untreated grafts and that they caught up by 4 weeks postimplantation. Histomorphometrics revealed that the intimal area was less in vitrified grafts at 2 weeks (p = 0.007) and that the luminal area was less in vitrified grafts at 4 weeks (p = 0.002). All other morphometric parameters were not significantly different. Smooth muscle physiology demonstrated a tendency for the responses of vitrified grafts to be lower than controls, not statistically significantly different to controls for three of the four contractile agonists at each time point or for relaxation induced by acetycholine. Sodium nitroprusside-induced relaxations appeared to be identical. Sensitivity to histamine was decreased at 2 weeks, and the sensitivity to norepinephrine was increased at 4 weeks in vitrified explants (<0.05). This study demonstrates that vitrification slows down the arterialization process; however, by the end of the month after implantation the vein grafts have similar smooth muscle functions and histology. The greatest concern regarding use of this method for preservation of blood vessels for clinical application was the statistically significant decrease in luminal area observed at 1 month. Longer term in vivo studies are required to determine whether or not the observed luminal decrease progresses to occlusion.