How do I bridge anticoagulation with Low Molecular Weight Heparin (LMWH) or Unfractionated Heparin (UFH) when starting warfarin in patients with atrial fibrillation?

Bridging Anticoagulation When Starting Warfarin in Atrial Fibrillation

For most patients with atrial fibrillation without mechanical heart valves, bridging therapy is NOT recommended when initiating warfarin, as it increases bleeding risk without reducing thromboembolism. 1

When to Bridge vs. When NOT to Bridge

DO NOT Bridge (Most Patients)

• Patients with nonvalvular AF at low to moderate thromboembolic risk (CHA₂DS₂-VASc score <7 or CHADS₂ score <5) should NOT receive bridging therapy when starting warfarin 2
• The landmark BRIDGE trial demonstrated that absence of bridging was noninferior to bridging with LMWH for preventing arterial thromboembolism and significantly decreased bleeding risk 1
• Simply start warfarin and allow the INR to rise naturally over 5-7 days without heparin overlap in these patients 2

DO Bridge (High-Risk Patients Only)

Bridging therapy with UFH or LMWH IS recommended for: 1

• Patients with mechanical heart valves (Class I recommendation)
• Recent stroke or TIA within 3 months 2
• Very high thromboembolic risk: CHA₂DS₂-VASc score ≥7 or CHADS₂ score of 5-6 2
• History of perioperative stroke 2

Bridging Protocol (When Indicated)

LMWH Bridging (Preferred)

• Enoxaparin 1 mg/kg subcutaneously every 12 hours (therapeutic dosing) 3, 4
• Start simultaneously with warfarin on day 1 3
• Continue LMWH until INR reaches therapeutic range (2.0-3.0) on two consecutive days 1
• LMWH offers advantages: longer half-life, predictable bioavailability >90%, once or twice-daily dosing, no laboratory monitoring required (except in obesity, renal insufficiency, pregnancy) 1
• Can be self-administered at home, potentially avoiding hospitalization 5

UFH Bridging (Alternative)

• Initial IV bolus of 5,000 units, followed by continuous infusion of 1,000 units/hour 6
• Adjust dose to maintain aPTT at 1.5-2 times control value 1, 6
• Continue until INR is therapeutic (2.0-3.0) for at least 24 hours 1
• Requires hospitalization and frequent aPTT monitoring 6

Warfarin Dosing

• Start warfarin on day 1 at typical maintenance dose (usually 5 mg daily, adjusted for age/body size) 1
• Target INR 2.0-3.0 1
• Check INR at least weekly during initiation, then monthly when stable 1
• Continue bridging anticoagulant for minimum 5 days AND until INR ≥2.0 on two consecutive measurements 1

Special Populations

Renal Impairment

• Reduce LMWH dose to once daily if GFR <30 mL/min 7
• Consider UFH instead if severe renal dysfunction, as it is not renally cleared 6
• Warfarin remains safe in end-stage CKD and dialysis patients 1

Elderly Patients (>75 years)

• Consider lower target INR of 2.0 (range 1.6-2.5) to reduce bleeding risk 1
• Women over 60 have higher bleeding incidence 6
• Use standard bridging protocols but monitor more closely 3

Common Pitfalls to Avoid

Critical Errors

• Do NOT use bridging in average-risk AF patients - this is the most common error and increases bleeding without benefit 1, 2
• Do NOT stop heparin/LMWH prematurely - continue until INR therapeutic for 24-48 hours, not just when INR first reaches 2.0 1
• Do NOT delay warfarin initiation - start warfarin and bridging agent simultaneously on day 1 2

Monitoring Failures

• Inadequate risk assessment leads to inappropriate bridging decisions 2
• Failure to check INR frequently enough during initiation (minimum weekly) 1
• Not recognizing that therapeutic INR takes 5-7 days even with bridging 1

Bleeding Risk Management

• Age and total LMWH dose are independent risk factors for bleeding 3
• Major bleeding occurs in 0.4% and minor bleeding in 8.9% with LMWH bridging 3
• Therapeutic-dose bridging increases bleeding compared to no bridging (3.2% vs 1.3% major bleeding in BRIDGE trial) 1

Alternative Approach: TEE-Guided Strategy

• For patients requiring urgent cardioversion, TEE can exclude left atrial thrombus 1
• If no thrombus present, can proceed with cardioversion after IV heparin bolus, then continue anticoagulation 1
• This approach may allow earlier cardioversion without 3-4 weeks of pre-anticoagulation 1, 5