Low-molecular-weight heparin in acute coronary syndromes

Acute coronary syndrome (ACS) may be divided into two distinct conditions on the basis of the electrographical presence or absence of significant ST-segment elevation. Coronary arterial plaque rupture with subsequent thrombus formation is usually responsible for the development of ACS. A number of antithrombotic therapies have been developed to inhibit key steps in the sequential process of thrombus formation. Thrombin generation is of critical importance in the creation of intracoronary thrombosis. Heparins, in therapeutic doses, reduce the risk of death and myocardial infarction by about 50% in aspirin-treated patients presenting with ACS with non-ST-segment elevation. Low-molecular-weight heparin (LMWH) primarily targets the inhibition of factor Xa (and to a lesser extent thrombin) by binding with antithrombin. A number of well-designed, large randomized controlled trials have shown that LMWHs have at least comparable efficacy and safety to unfractionated heparin, but their superior practical advantages have made them a mainstay therapy in the treatment of ACS with non-ST-segment elevation. More recently, the role of LMWH in the treatment of ACS with ST elevation has been evaluated in a large randomized trial.