Altered plasma antigen levels of tissue factor pathway inhibitor during open-heart surgery

Tissue factor pathway inhibitor (TFPI) is a potent inhibitor of the extrins ic pathway of the coagulation cascade that is activated by cardiopulmonary bypass (CPB) during open-heart surgery, In the present study, we investigat ed whether the plasma TFPI antigen increases during CPB in 12 patients who underwent bypass procedures. The plasma levels of free and total TFPI antig ens were measured using an enzyme-linked immunosorbent assay, and heparin c oncentrations were measured using a chromogenic substrate assay. We found t hat changes in the total plasma TFPI antigen level were significantly depen dent on the level of free TFPI antigen (r = 0.96, P < 0.0001) which increas ed significantly after heparin injection (P < 0.0001), and increased furthe r during the bypass period (P < 0.005), The increased free TFPI antigen lev el during CPB correlated with the duration of bypass (r = 0.65, P = 0.02). When heparin was neutralized by protamine, the free TFPI antigen level decr eased immediately, but remained higher than the preoperative level (P < 0.0 05). These results suggest that plasma TFPI antigen levels increase during CPB.