BACKGROUND: Pharmacological coronary fibrinolysis induces procoagulant effects that contribute to delayed recanalization and early reocclusion. This study was designed to determine whether brief inhibition of activation of the coagulation cascade with tissue factor pathway inhibitor, a physiological inhibitor of activated factor X and its activation by the tissue factor/factor VII complex, would facilitate fibrinolysis, sustain patency of recanalized arteries, or both. METHODS AND RESULTS: Platelet-rich coronary thrombi were induced with anodal current that elicited intimal injury in 21 conscious dogs. Each was randomized to human recombinant tissue-type plasminogen activator (rTPA 1.0 mg/kg IV over 1 hour) with infusion of 50 micrograms.kg-1.min-1 of human recombinant tissue factor pathway inhibitor (rTFPI, n = 7), 100 micrograms.kg-1.min-1 of rTFPI (n = 8), or 300 mmol/L arginine phosphate buffer as a control (n = 6) concomitant with and for 1 hour after infusion of the plasminogen activator. Recanalization, verified with proximal Doppler flow probes, occurred in all but 1 dog given the high dose of rTFPI. It was not accelerated by conjunctive rTFPI. Reocclusion occurred within 90 minutes after infusion of rTPA in all 6 control dogs. However, reocclusion was delayed and patency was sustained for the entire 24-hour observation interval in 2 of 6 dogs (excluding 1 that did not survive) given the low dose and in 4 of 6 dogs (excluding 1 that did not receive the desired amount) given the high dose of rTFPI (P < .05 compared with controls). Cyclic flow variations indicative of platelet aggregation and disaggregation locally were virtually eliminated by rTFPI (3 +/- 4[SD]/h in dogs given the low dose and 2 +/- 2/h in those given the high dose of rTFPI compared with 13 +/- 12/h in controls, P < .05). In addition, rTFPI increased activated partial thromboplastin time and prothrombin time only at the high dose (1.4 +/- 0.3 and 2.1 +/- 0.9 times baseline) and had no effects on platelet aggregation assayed ex vivo and only minimal effects on bleeding time assayed in vivo. CONCLUSIONS: Brief inhibition of the coagulation system by administration of rTFPI sustains patency of arteries recanalized by pharmacological fibrinolysis without markedly perturbing hemostatic mechanisms.
BACKGROUND: Pharmacological coronary fibrinolysis induces procoagulant effects that contribute to delayed recanalization and early reocclusion. This study was designed to determine whether brief inhibition of activation of the coagulation cascade with tissue factor pathway inhibitor, a physiological inhibitor of activated factor X and its activation by the tissue factor/factor VII complex, would facilitate fibrinolysis, sustain patency of recanalized arteries, or both. METHODS AND RESULTS: Platelet-rich coronary thrombi were induced with anodal current that elicited intimal injury in 21 conscious dogs. Each was randomized to human recombinant tissue-type plasminogen activator (rTPA 1.0 mg/kg IV over 1 hour) with infusion of 50 micrograms.kg-1.min-1 of human recombinant tissue factor pathway inhibitor (rTFPI, n = 7), 100 micrograms.kg-1.min-1 of rTFPI (n = 8), or 300 mmol/L arginine phosphate buffer as a control (n = 6) concomitant with and for 1 hour after infusion of the plasminogen activator. Recanalization, verified with proximal Doppler flow probes, occurred in all but 1 dog given the high dose of rTFPI. It was not accelerated by conjunctive rTFPI. Reocclusion occurred within 90 minutes after infusion of rTPA in all 6 control dogs. However, reocclusion was delayed and patency was sustained for the entire 24-hour observation interval in 2 of 6 dogs (excluding 1 that did not survive) given the low dose and in 4 of 6 dogs (excluding 1 that did not receive the desired amount) given the high dose of rTFPI (P < .05 compared with controls). Cyclic flow variations indicative of platelet aggregation and disaggregation locally were virtually eliminated by rTFPI (3 +/- 4[SD]/h in dogs given the low dose and 2 +/- 2/h in those given the high dose of rTFPI compared with 13 +/- 12/h in controls, P < .05). In addition, rTFPI increased activated partial thromboplastin time and prothrombin time only at the high dose (1.4 +/- 0.3 and 2.1 +/- 0.9 times baseline) and had no effects on platelet aggregation assayed ex vivo and only minimal effects on bleeding time assayed in vivo. CONCLUSIONS: Brief inhibition of the coagulation system by administration of rTFPI sustains patency of arteries recanalized by pharmacological fibrinolysis without markedly perturbing hemostatic mechanisms.