What is Bridging in Anticoagulant Therapy
Bridging anticoagulation is the administration of a short-acting parenteral anticoagulant—either subcutaneous low-molecular-weight heparin (LMWH) or intravenous unfractionated heparin (UFH)—during the 10-12 day period when chronic oral anticoagulants (typically warfarin) are temporarily interrupted for elective procedures or surgery. 1
Core Concept
Bridging therapy aims to maintain anticoagulation protection during the vulnerable period when vitamin K antagonists (VKAs) like warfarin are stopped before a procedure and not yet therapeutic after resumption. 1 The rationale is that continuing oral anticoagulation increases bleeding risk during procedures, while complete absence of anticoagulation increases thromboembolic risk. 1
Mechanism and Timing
Preoperative phase: Warfarin is stopped 5-6 days before the procedure to allow INR normalization. 2 When the INR drops below the therapeutic threshold (typically 2.0-2.5), bridging with therapeutic-dose LMWH or UFH is initiated, usually 36-48 hours before surgery. 1
Immediate preoperative: The bridging anticoagulant is stopped 4-6 hours before the procedure for intravenous UFH, or 12-24 hours before for subcutaneous LMWH, to minimize bleeding risk at the time of surgery. 1, 2
Postoperative phase: Warfarin is resumed the evening after surgery once hemostasis is confirmed. 2 Bridging anticoagulation is restarted 24 hours after low-bleeding-risk procedures or delayed 48-72 hours after high-bleeding-risk procedures, and continued until the INR returns to therapeutic range. 2
Standard Bridging Regimens
Three dose intensities have been studied, though therapeutic-dose is most commonly used for arterial thromboembolism prevention: 1
Therapeutic-dose: Enoxaparin 1 mg/kg twice daily or 1.5 mg/kg once daily; dalteparin 100 IU/kg twice daily or 200 IU/kg once daily; tinzaparin 175 IU/kg once daily; or IV UFH titrated to aPTT 1.5-2 times control. 1
Prophylactic-dose: Enoxaparin 30 mg twice daily or 40 mg once daily; dalteparin 5,000 IU once daily; UFH 5,000-7,500 IU twice daily. 1
Intermediate-dose: Enoxaparin 40 mg twice daily, representing an intensity between therapeutic and prophylactic dosing. 1
Critical Evidence Limitations
The evidence supporting bridging therapy is weak, consisting primarily of observational studies with methodological concerns and no randomized placebo-controlled trials demonstrating benefit. 1 Recent cohort studies and randomized trials consistently show that heparin bridging increases major bleeding risk two- to three-fold without reducing stroke or systemic embolism risk in most patient populations. 3
When Bridging May Be Considered
Bridging should only be considered for patients at high thromboembolic risk, which includes: 2
- Mechanical mitral valve prosthesis
- Any mechanical valve with atrial fibrillation
- Non-valvular atrial fibrillation with CHA₂DS₂-VASc score >5
- Recent venous thromboembolism (<3 months)
- Severe thrombophilia (protein C or S deficiency, antiphospholipid syndrome)
The majority of patients on chronic warfarin, except those at high thromboembolic risk, may safely interrupt and resume warfarin without heparin bridging. 3
Novel Oral Anticoagulants (NOACs)
Bridging therapy is generally not required for patients on direct oral anticoagulants (dabigatran, rivaroxaban, apixaban) due to their short half-lives (typically 12-14 hours), rapid onset and offset of action, and predictable pharmacokinetics. 4, 5 The rapid pharmacokinetic properties of NOACs obviate the need for heparin bridging, and evidence shows increased bleeding risk without reduction in thromboembolic events when bridging is used with these agents. 4, 3
Common Pitfalls
- Over-bridging: Using bridging in moderate or low-risk patients increases bleeding without reducing thrombosis. 3
- Timing errors: Administering LMWH within 12 hours of surgery leaves 34% of patients with therapeutic anticoagulation at the time of the procedure. 6
- Premature postoperative resumption: Restarting therapeutic-dose anticoagulation within 12-24 hours of high-bleeding-risk surgery increases major bleeding rates up to 20%. 6
- Unnecessary bridging with NOACs: These agents do not require bridging due to their pharmacokinetic properties. 4