Thrombin generation after the abrupt cessation of intravenous unfractionated heparin among patients with acute coronary syndromes - Potential mechanisms for heightened prothrombotic potential

OBJECTIVES The purpose of this study was to determine the mechanistic basis for thrombin generation and increased prothrombotic potential after the ab rupt cessation of intravenous (IV) unfractionated heparin among patients wi th acute coronary syndromes. BACKGROUND A "rebound" increase in prothrombotic potential has been observe d biochemically and clinically after the abrupt cessation of unfractionated heparin (UFH) among patients with acute coronary syndromes. Although the m echanism is unknown, tissue factor and the extrinsic coagulation cascade, b oth operative in atherosclerotic vascular disease and arterial thrombosis, are thought to be centrally involved. METHODS In a single-center, pilot study, 30 patients with either unstable a ngina or non-ST segment elevation myocardial infarction who had received a continuous IV infusion of UFH for 48 h were randomly assigned to: 1) abrupt cessation, 2) IV weaning over 12 h or 3) subcutaneous weaning over 12 h. RESULTS Thrombin generation (prothrombin fragment 1.2) was evident within 1 h of UFH cessation, increased progressively (by nearly two-fold) at 24 h ( p = 0.002) and correlated inversely with tissue factor pathway inhibitor co ncentration (r = -0.61). Thrombin generation was greatest among patients ra ndomized to abrupt cessation (1.6-fold increase at 24 h) and least in those with IV weaning. CONCLUSIONS Thrombin generation after the abrupt cessation of UFH may repre sent a drug-induced impairment of physiologic vascular thromboresistance in response to locally generated tissue factor. A dosing strategy of abbrevia ted ITT weaning attenuates but does not prevent heparin rebound among patie nts with acute coronary syndromes. (J Am Coll. Cardiol 1999;34:1020-7) (C) 1999 by the American College of Cardiology.