What is the recommended heparin (unfractionated heparin) drip protocol for bridging to warfarin in a patient with atrial fibrillation (AFib) and a mechanical valve?

Heparin Bridging Protocol for AFib with Mechanical Valve

Bridging therapy with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) is mandatory for patients with atrial fibrillation and a mechanical heart valve when warfarin must be interrupted for procedures. 1

Why Bridging is Required in This Population

• Patients with mechanical heart valves face extremely high thromboembolic risk (>10% annually) when anticoagulation is interrupted, making bridging non-negotiable regardless of CHA₂DS₂-VASc score 1, 2
• The mechanical valve itself mandates bridging—this is fundamentally different from non-valvular AFib where bridging is generally avoided 3, 2
• DOACs remain absolutely contraindicated (Class III: Harm) in mechanical valve patients, so warfarin is the only option for chronic anticoagulation 3

Specific Bridging Protocol

Pre-Procedure Management

• Stop warfarin 5 days before the procedure 1
• Start bridging anticoagulation when INR falls below 2.0 (typically 36-48 hours after last warfarin dose) 1, 2
• LMWH is preferred over UFH due to outpatient administration capability, predictable bioavailability, and no monitoring requirements 1, 2
• LMWH dosing: therapeutic dose twice daily (e.g., enoxaparin 1 mg/kg subcutaneously every 12 hours), adjusted for body weight and renal function 1
• Alternative UFH dosing: continuous IV infusion targeting aPTT 1.5-2.5 times control, though this requires hospitalization 1
• Stop LMWH 24 hours before the procedure (give last dose 24 hours pre-operatively) 2
• If using UFH, stop 4-6 hours before procedure 1

Post-Procedure Management

• Resume warfarin the evening of the procedure at the usual maintenance dose 2
• Resume bridging anticoagulation 24 hours post-operatively or when adequate hemostasis is secured 1, 2
• Continue bridging until INR reaches therapeutic range (2.0-3.0) on two consecutive measurements, not just when INR first reaches 2.0 2
• For mechanical mitral valves or older-generation valves, target INR is 2.5-3.5; for bileaflet aortic valves without risk factors, target is 2.0-3.0 3

Critical Monitoring Considerations

If Using LMWH (Preferred)

• Monitor anti-Xa levels if available, targeting 0.5-1.0 U/mL, particularly in patients with renal insufficiency (CrCl <30 mL/min), obesity (>120 kg or BMI >35), or pregnancy 1
• No routine monitoring needed in standard patients 2

If Using UFH

• Use lower-intensity protocols to reduce bleeding risk: target aPTT 1.5-2.0 times control rather than higher targets 4
• Low-intensity UFH (targeting lower anticoagulation) was associated with decreased bleeding (4.9% vs 10.5%) without increased thrombotic events in hospitalized AFib patients 4
• Check aPTT every 6 hours until stable, then daily 1

Evidence-Based Nuances

Why This Population is Different

• The landmark BRIDGE trial showed no bridging was superior in non-valvular AFib, but mechanical valve patients were specifically excluded from this trial 1, 2
• Meta-analyses confirm that in mechanical valve patients, bridging carries a 2.8% major bleeding risk but only 0.9% thromboembolism risk, making the risk-benefit ratio favorable 1
• In contrast, non-valvular AFib patients have 3-fold increased bleeding with bridging and no reduction in stroke 2

LMWH vs UFH Comparison

• LMWH and UFH have equivalent efficacy for mechanical valve bridging in observational studies 1, 5
• LMWH offers practical advantages: outpatient use, no monitoring in most cases, and potentially lower bleeding rates 2, 5
• UFH remains the only FDA-approved heparin for mechanical valves, though LMWH is widely used off-label 1

Common Pitfalls to Avoid

• Never use DOACs for bridging or chronic anticoagulation in mechanical valve patients—this increases both thromboembolism and bleeding 3
• Do not stop bridging prematurely: continue until INR is therapeutic for 24-48 hours, not just when it first reaches 2.0 2
• Avoid combining bridging with antiplatelet therapy unless absolutely necessary (e.g., recent coronary stent), as this increases bleeding risk by >50% without clear benefit 2
• Do not use fondaparinux for bridging in mechanical valve patients—it is not validated for this indication 1
• Avoid high-intensity UFH protocols (targeting aPTT >2.5 times control) as they increase bleeding without reducing thrombosis 4

Special Circumstances

High Bleeding Risk Procedures

• For procedures with very high bleeding risk, consider delaying bridging resumption beyond 24 hours post-operatively until hemostasis is definitively secured 1
• Restart warfarin on schedule but delay heparin restart by 48-72 hours if needed 1

Renal Insufficiency

• Adjust LMWH doses for CrCl <30 mL/min and monitor anti-Xa levels 1
• Consider UFH instead of LMWH in severe renal impairment (CrCl <15 mL/min) due to unpredictable LMWH clearance 1

Subtherapeutic INR During Routine Monitoring

• If INR falls below therapeutic range during routine outpatient monitoring (not peri-procedurally), initiate bridging with LMWH or UFH until therapeutic INR is re-established 1