Anticoagulation in Acute Coronary Syndromes

Clinical Scenario-Based Algorithm

The American Heart Association recommends that for patients with NSTE-ACS managed conservatively, fondaparinux 2.5 mg subcutaneous daily is the preferred agent, as it demonstrated equivalent ischemic outcomes to enoxaparin but with significantly reduced major bleeding in the OASIS-5 trial 2
For patients with NSTE-ACS, enoxaparin 1 mg/kg subcutaneous every 12 hours is an equally reasonable alternative, with proven superiority over UFH in reducing death/MI/recurrent angina (16.6% vs 19.6% at 14 days) in the ESSENCE trial 2, 3
The American College of Cardiology recommends that UFH is acceptable but offers no advantage over LMWH in this setting, with meta-analyses showing no significant difference in death or MI (2.2% vs 2.3%) 2
For patients with STEMI undergoing fibrinolytic therapy, enoxaparin is superior to UFH, with dosing adjusted by age: Age <75 years: 30 mg IV bolus, then 1 mg/kg subcutaneous every 12 hours (maximum 100 mg first two doses), Age ≥75 years: no bolus, 0.75 mg/kg subcutaneous every 12 hours (maximum 75 mg first two doses) 1, 2
For patients with STEMI undergoing primary PCI, UFH remains the standard anticoagulant due to immediate onset, ACT monitoring capability, and protamine reversibility 1, 2

LMWH (enoxaparin) has more predictable anticoagulation without need for aPTT monitoring due to reduced plasma protein binding, and lower risk of heparin-induced thrombocytopenia (64% reduction) compared to UFH 5
UFH has immediate reversibility with protamine for patients at high bleeding risk or needing urgent procedures, and ACT-guided dosing during PCI allows real-time adjustment 1, 2, 5
Fondaparinux has the lowest bleeding risk among all anticoagulants in ACS, with superior bleeding profile versus enoxaparin in OASIS-5, but is contraindicated if CrCl <30 mL/min 1, 2

Never use fondaparinux alone for PCI support, as the 0.9% catheter thrombosis rate mandates adding UFH if PCI becomes necessary 1, 2
Do not abruptly discontinue anticoagulation, as premature cessation causes rebound thrombin activation with greatest reinfarction risk at 4-8 hours 1, 2
Adjust enoxaparin dosing in renal dysfunction: reduce to 1 mg/kg daily if CrCl <30 mL/min; consider UFH if CrCl <15 mL/min 1, 5

Continue anticoagulation until revascularization (PCI or CABG) is performed 1, 2
For medical management, typical duration is 2-8 days (median 2.6 days in ESSENCE trial) 3
There is no proven benefit for prolonged outpatient LMWH beyond acute phase in ACS, unlike VTE treatment 3, 5