Do I need to start heparin (unfractionated heparin or low molecular weight heparin) for anticoagulation when holding warfarin (coumarin) due to a procedure if the International Normalized Ratio (INR) is within the therapeutic range?

Bridging Anticoagulation Timing for Warfarin Interruption

Start heparin bridging therapy immediately when warfarin is held, without waiting for the INR to become subtherapeutic. 1, 2

When to Initiate Bridging Therapy

For high-risk patients (mechanical heart valves, recent VTE <3 months, atrial fibrillation with prior stroke), bridging anticoagulation with therapeutic-dose heparin (UFH or LMWH) should begin 1-2 days after stopping warfarin, not after the INR drops below therapeutic range. 1

The specific timing is:

• Stop warfarin 5 days before the procedure 1
• Start LMWH 2 days after stopping warfarin (1 day after acenocoumarol) 1
• Do not wait for INR to become subtherapeutic before starting bridging 1, 2

Rationale for Early Bridging Initiation

The critical concept here is that warfarin has a half-life of approximately 42 hours, and therapeutic anticoagulation wanes progressively after discontinuation. 2 Waiting until the INR drops below 2.0 creates an unprotected window where the patient has inadequate anticoagulation but no bridging coverage. 2

Bridging therapy is designed to provide continuous anticoagulation coverage during the entire period when warfarin effect is declining and subtherapeutic. 1

High-Risk vs Low-Risk Patients

High-Risk Patients Requiring Bridging 1:

• Mechanical heart valves (especially mitral position or older-generation valves) 1
• Atrial fibrillation with prior stroke/TIA or CHA₂DS₂-VASc ≥2 1
• Recent VTE (<3 months) 1
• Thrombophilia or hypercoagulable conditions 1

Low-Risk Patients (No Bridging Needed) 1:

• Bileaflet mechanical AVR without additional risk factors 1
• Can simply hold warfarin 5 days before procedure without bridging 1

Specific Bridging Protocol

For patients requiring bridging: 1, 2

1. Stop warfarin 5 days (5 doses) before surgery 1
2. Start therapeutic-dose LMWH 2 days after stopping warfarin 1
   • Enoxaparin 1 mg/kg subcutaneous every 12 hours 2
   • Target anti-Xa level 0.8-1.2 U/mL 2
3. Give last dose of LMWH at least 12-24 hours before the procedure 1
4. Check INR on day of procedure (should be <1.5) 1

Postoperative Resumption

Resume warfarin on the evening of surgery (day 1-2 postoperatively) at the usual maintenance dose. 1, 2, 3

Restart therapeutic-dose LMWH or UFH 12-48 hours after surgery depending on bleeding risk and hemostatic stability. 1, 4

• Low bleeding risk procedures: restart at 12-24 hours 4
• High bleeding risk procedures: restart at 48-72 hours 1, 4

Continue bridging therapy until INR returns to therapeutic range (typically 4-5 days of overlap). 1, 2, 5, 3

Common Pitfalls to Avoid

Do not wait for a subtherapeutic INR before starting bridging—this creates a dangerous gap in anticoagulation coverage. 2 The entire point of bridging is to maintain anticoagulation during the transition period when warfarin is wearing off.

Do not restart therapeutic-dose heparin too early postoperatively in high bleeding risk procedures—this significantly increases bleeding complications. 1, 4 Prophylactic-dose heparin can be given at 12 hours, but therapeutic dosing should wait 48-72 hours if bleeding risk is high. 1, 4

For mechanical valves, never skip bridging therapy—these patients are at extremely high risk for valve thrombosis during even brief periods without anticoagulation. 1, 2