What is the role of heparin (unfractionated heparin (UFH) or low molecular weight heparin (LMWH)) in patients with atrial fibrillation?

Role of Heparin in Atrial Fibrillation

For most patients with nonvalvular atrial fibrillation, heparin bridging therapy should NOT be used when starting or interrupting oral anticoagulation, as it significantly increases bleeding risk (2-3 fold) without reducing stroke risk. 1

When Heparin Should NOT Be Used (Most Patients)

Avoid bridging anticoagulation in the following scenarios:

• Low to moderate thromboembolic risk patients (CHA₂DS₂-VASc score <7 or CHADS₂ score <5) starting warfarin therapy 1
• Perioperative interruption of anticoagulation for up to 1 week in patients without mechanical valves 2
• Average-risk AF patients undergoing elective procedures—this is the most common error in practice 1

The evidence is compelling: bridging increases major bleeding from 0.5% to 2.7% (p=0.01) without reducing thromboembolism 1, and meta-analysis shows major bleeding odds ratio of 0.41 favoring no bridging (95% CI 0.24-0.68, p=0.0006) 3.

When Heparin IS Indicated (High-Risk Patients Only)

Reserve heparin bridging exclusively for very high thromboembolic risk:

• Mechanical heart valves (particularly older-generation or mitral position) 2, 1
• Recent stroke or TIA within 3 months 1
• History of perioperative stroke 1
• AF with mitral stenosis 4

Specific Clinical Scenarios for Heparin Use

Cardioversion Anticoagulation

For AF duration ≥48 hours or unknown duration:

• Start IV unfractionated heparin or LMWH immediately at presentation 4
• Continue anticoagulation for 3 weeks before cardioversion and at least 4 weeks after 4
• Alternative strategy: immediate TEE screening with heparin cover, then cardioversion if no thrombus 4

For AF duration <48 hours:

• Begin IV heparin or LMWH at presentation despite shorter duration 4
• Cardioversion can proceed without 3-week waiting period 4

Acute AF Management

FDA-approved indication: Heparin is indicated for atrial fibrillation with embolization 5

LMWH vs. Unfractionated Heparin

When bridging is truly necessary, LMWH is preferred over UFH:

Advantages of LMWH:

• Longer half-life and predictable bioavailability (>90%) 2
• Once or twice-daily subcutaneous dosing 2
• No laboratory monitoring required (except obesity, renal insufficiency, pregnancy) 2, 1
• Outpatient administration capability 1
• Enables self-administration and potential cost savings 2

Clinical equivalence: LMWH (enoxaparin 60mg SC q12h) shows similar efficacy to UFH (1000 units/h IV) with comparable bleeding rates (13.5% vs 18.9%, p=0.754) and thrombotic events 6

Proper Bridging Protocol (When Indicated)

If bridging is absolutely necessary:

1. Stop warfarin 5 days before procedure 1
2. Start LMWH 3 days before procedure (36-48 hours after last warfarin dose) 1
3. Stop LMWH 24 hours before procedure 1
4. Resume warfarin evening of procedure at usual maintenance dose 1
5. Resume LMWH 24 hours postoperatively when hemostasis secured 1
6. Continue LMWH until INR reaches 2.0-3.0 on two separate measurements 1

Critical Pitfalls to Avoid

Do not combine bridging with antiplatelet therapy: The combination of warfarin plus aspirin increases major bleeding to 4.95% per year compared to 1.5% with warfarin alone (p=0.004) 1

Do not use high-intensity UFH regimens: High-intensity UFH increases bleeding (10.5% vs 4.9%, OR 2.29,95% CI 1.07-4.90) without reducing thrombotic events 7. Low-intensity targeting is safer 7.

Do not stop heparin prematurely: Continue until INR is therapeutic for 24-48 hours, not just when INR first reaches 2.0 1

Do not bridge routinely in elderly patients: Consider lower target INR of 2.0 (range 1.6-2.5) in patients >75 years to reduce bleeding risk 1