Anticoagulation Strategy for Acute Coronary Syndrome in Patients Receiving Therapeutic Warfarin (INR ≈ 2.5)

1. Bleeding Risk with Dual Anticoagulation

Adding low‑molecular‑weight heparin (enoxaparin) to therapeutic warfarin creates a dual anticoagulation state that markedly raises major bleeding risk; enoxaparin’s limited reversibility and lack of a reliable monitoring parameter further exacerbate this danger. American College of Cardiology (ACC) recommendation – Class IIb, Level A. 1

Unfractionated heparin (UFH) is the recommended anticoagulant for ACS patients on warfarin because its effect can be titrated with aPTT monitoring and rapidly reversed with protamine, allowing precise control of anticoagulation in the presence of baseline warfarin therapy. ACC/AHA/ACEP/NAEMSP/SCAI guideline – Class I, Level A. 1

Initiate UFH with a reduced bolus (≈ 50 U/kg) and a lower infusion rate (≈ 10–12 U/kg/h), targeting an aPTT of 1.5 × control rather than the standard 2.0 × control, to account for the additive anticoagulant effect of warfarin. ACC recommendation – Class IIa, Level B. 1

Hold warfarin and start UFH at standard dosing (70 U/kg bolus, 15 U/kg/h infusion) until the INR falls below 2.0. After INR normalization, enoxaparin 1 mg/kg subcutaneously twice daily may be used as an alternative to UFH for ongoing ACS care. ACC guidance – Class IIb, Level B. 1

Perform early coronary angiography and revascularization when clinically indicated, using UFH with ACT monitoring throughout the procedure. Bivalirudin can be considered as an alternative to reduce bleeding risk in non‑ST‑elevation ACS (Class IIb, Level B). ACC/AHA/ACEP/NAEMSP/SCAI guideline – Class IIb. 1
Fondaparinux should be avoided as the sole anticoagulant during PCI because of a heightened risk of catheter thrombosis (Class III, Harm). 1

The combination of warfarin, aspirin, and a P2Y12 inhibitor (clopidogrel or ticagrelor) substantially increases major bleeding risk, even without additional parenteral anticoagulation. Circulation evidence – observational data, Level C. 2
When triple therapy is unavoidable post‑PCI, use low‑dose aspirin (≤ 100 mg daily) to mitigate bleeding. 2

Continue UFH until successful PCI or clinical stabilization is achieved; if the patient is managed conservatively without revascularization, maintain UFH for the hospital stay, not exceeding 8 days. ACC recommendation – Class I, Level A. 1
After PCI, discontinue UFH and resume warfarin with an appropriate bridging strategy if long‑term anticoagulation remains indicated. 1