Transgraft infusion of heparin to prevent early thrombosis of expanded PTFE grafts in canine femoral veins

Local infusion of heparin reduces anastomotic neointimal hyperplasia in aortoiliac expanded polytetrafluoroethylene bypass grafts in baboons

PURPOSE

Recently, we designed and characterized a novel expanded polytetrafluoroethylene (ePTFE)-based local drug delivery approach that selectively concentrates infused pharmacologic agents specifically within those blood layers adjacent to the graft wall and at downstream anastomotic sites. In this study, we locally administrated standard heparin therapy and evaluated its effects on neointimal hyperplasia formation in a baboon model of aortoiliac bypass graft placement.

METHODS

Six adult male baboons underwent bilateral aortoiliac bypass grafting with ringed ePTFE (4 mm internal diameter x 5 cm length). In each animal, the distal anastomosis of one graft was continuously infused with heparin (50 U/h) and the distal anastomosis of the contralateral graft was infused with saline solution at the same rate (2.5 microL/h), with osmotic pumps implanted for 4 weeks. Platelet counts and activated partial thromboplastin time measurements were performed weekly. The specimens were harvested at 4 weeks and were subjected to morphometric analysis. Cell proliferation was assessed with bromodeoxyuridine immunostaining.

RESULTS

All the harvested grafts were patent except for one control graft. There were no significant differences in platelet counts or activated partial thromboplastin time measurements taken before and during heparin infusion. As expected, there were no significant differences in graft neointimal hyperplasia and cell proliferation at the proximal anastomoses between the heparin-infused and control grafts. In contrast, at the treated distal anastomoses, heparin infusion significantly reduced the graft neointimal area by 65% and the cell proliferation index by 47% as compared with the untreated control distal anastomoses.

CONCLUSION

These results show that local infusion of heparin significantly reduces distal anastomotic neointimal hyperplasia and cell proliferation without measurable systemic anticoagulation or other side effects. Thus, this approach may represent an attractive strategy for prolonging ePTFE bypass graft patency.

Phosphorylcholine coating of ePTFE reduces platelet deposition and neointimal hyperplasia in arteriovenous grafts

In an attempt to reduce platelet deposition and inhibit neointimal hyperplasia, we evaluated the effect of coating expanded polytetrafluoroethylene (ePTFE) grafts with phosphorylcholine (PC), a lipid found in animal cell membranes, in a dog model of femoral arteriovenous (AV) grafts. Eight mongrel dogs underwent placement of a PC-coated femoral AV graft on one side and an untreated control graft on the contralateral side. Platelet deposition was measured by autologous 111Indium-labeling and scintillation camera imaging analysis. Platelet deposition on the PC-coated grafts at 30 and 90 min. was 9.32 +/- 4.35 x 10(9) and 10.00 +/- 4.38 x 10(9), respectively, as compared with 10.26 +/- 4.36 x 10(9) and 11.64 +/- 5.08 x 10(9) platelet deposition on control grafts (P < 0.05). All grafts were patent at 4 weeks. There was a significant reduction of neointimal area at both arterial (0.07 +/- 0.05 mm2) and venous (0. 18 +/- 0.09 mm2) anastomoses in the treated grafts as compared with arterial (0.15 +/- 0.05 mm2) and venous (0.43 +/- 0.22 mm2) anastomoses in the control grafts (P < 0.05). In addition, neointimal cell proliferation assayed by bromodeoxyuridine (BrdU) incorporation was reduced in both arterial (2.05 +/- 0.81%) and venous (3.25 +/- 0.17%) anastomoses of treated grafts compared with arterial (3.12 +/- 1.23%) and venous (5.36 +/- 1.18%) anastomoses of control grafts (P < 0.05). These data demonstrated that PC coating of ePTFE grafts significantly reduced platelet deposition, anastomotic neointimal hyperplasia, and neointimal cell proliferation in a dog model of AV grafts. This may represent a new strategy for prolonging hemodialysis graft patency.