Enhancement of tissue factor expression by vein segments exposed to coronary arterial hemodynamics

Although saphenous vein is the most reliable conduit for arterial interposition procedures in the coronary circulation, graft thrombosis remains a clinical problem. We hypothesized that an important factor in early graft thrombosis is sudden change in the hemodynamic environment of the vein as it is placed in the coronary circulation.

We used an ex vivo perfusion system to study freshly excised segments of human saphenous vein (HSV) and pig internal jugular vein. For coronary graft (CAVG) simulation, sections of HSV were subjected to arterial pulsatile pressure and flow and twisting and stretching to mimic deformations caused by the beating heart. Using functional and immunohistochemical assays, we investigated the effect of these conditions on expression of tissue factor (TF), an important prothrombotic surface molecule.

In each of 11 experiments (6 human, 5 porcine), vein segments from a single donor were subjected to venous conditions (VEN), CAVG perfusion, or no perfusion. Expression of TF was measured as the amount of factor Xa generated per unit area of luminal vein surface. VEN perfusion did not cause a significant change in mean TF expression over nonperfused control values (human: 14.3 +/- 1.5 versus 11.4 +/- 2.3 U/cm2, p = 0.31; pig: 11.6 +/- 1.5 versus 12.5 +/- 1.4 U/cm2, p = 0.70). CAVG perfusion led to significant enhancement of TF expression over VEN perfusion (human: 36.8 +/- 6.2 versus 14.3 +/- 1.5 U/cm2, p < 0.05; pig: 40.0 +/- 9.9 versus 11.6 +/- 1.5 U/cm2, p < 0.05). Immunohistochemical analysis showed positive TF staining on the luminal side of a CAVG-stimulated HSV segment, but not on a VEN-stimulated segment. In four additional studies, HSV segments were subjected to arterial perfusion without twist and stretch to mimic lower extremity arterial interposition grafts. TF expression for lower extremity venous graft perfusion was significantly higher than for VEN perfusion (25.3 +/- 2.5 versus 14.3 +/- 1.5, p < 0.01) but not significantly different from CAVG perfusion.

Our studies in a unique perfusion system suggest that exposure of vein to coronary arterial hemodynamic conditions results in elevated expression of the important prothrombotic molecule TF. This phenomenon may contribute to early graft thrombosis.