Why is heparin used to bridge anticoagulation in patients on acenocoumarol (acitrom)?

Why Heparin Bridging is Used with Acenocoumarol (Acitrom)

Heparin bridging is used to maintain anticoagulation during the 2-4 day period when acenocoumarol (a vitamin K antagonist like warfarin) is stopped before surgery, but only in patients at high thromboembolic risk—most patients do NOT need bridging. 1

The Core Rationale

Acenocoumarol, like all vitamin K antagonists (VKAs), takes several days to wear off after discontinuation and several days to become therapeutic again after resumption. 1 This creates a vulnerable window where patients are unprotected from thromboembolism. Heparin (either unfractionated heparin or low-molecular-weight heparin) has a rapid onset and offset of action, allowing it to "bridge" this gap. 1

Critical Evidence: Most Patients Should NOT Be Bridged

The landmark BRIDGE trial (2019) definitively showed that bridging causes more harm than benefit in most patients with atrial fibrillation. 1 Patients who did not receive bridging had:

• Non-inferior rates of arterial thromboembolism compared to bridged patients
• Significantly lower bleeding rates than bridged patients 1

This finding has fundamentally changed practice: bridging is now reserved only for the highest-risk patients. 1

Who Actually Needs Bridging

High-Risk Patients Requiring Bridging: 1

• Mechanical mitral valve (any type)
• Older-generation mechanical aortic valve
• Bileaflet mechanical aortic valve PLUS additional thromboembolic risk factors (stroke/TIA within 6 months, multiple prior thromboembolic events, left atrial thrombus, severe left ventricular dysfunction)
• Recent thromboembolism (<3 months) 2

Patients Who Do NOT Need Bridging: 1

• Bileaflet mechanical aortic valve with NO other risk factors (bridging NOT recommended) 1
• Atrial fibrillation without mechanical valves (bridging causes net harm) 1
• Venous thromboembolism >3 months ago 2
• Bioprosthetic valves (consider bridging based on CHA₂DS₂-VASc score, but generally not needed) 1

The Pharmacologic Gap That Bridging Addresses

Why the Gap Exists:

• Acenocoumarol must be stopped 2-4 days before surgery to allow INR to normalize 1
• After surgery, acenocoumarol takes several days to reach therapeutic INR again 1
• This creates a 5-7 day window of subtherapeutic anticoagulation 1

How Heparin Fills the Gap:

• LMWH (enoxaparin 1 mg/kg twice daily or dalteparin 100 IU/kg twice daily) provides immediate therapeutic anticoagulation 1
• Last preoperative dose given 24 hours before surgery (not 12 hours) to minimize bleeding risk 1
• Postoperative resumption delayed 48-72 hours after major surgery to ensure hemostasis 1
• Unfractionated heparin IV is an alternative for patients with severe renal insufficiency 1

Common Pitfalls to Avoid

Pitfall #1: Over-bridging Low-Risk Patients

The most common error is bridging patients who don't need it. 1, 3 Recent evidence shows bridging increases bleeding risk 2-3 fold without reducing thromboembolism in most patients. 3

Pitfall #2: Resuming Heparin Too Soon After Surgery

Starting therapeutic-dose LMWH within 12-24 hours postoperatively increases major bleeding by 20% after major surgery. 1 Wait 48-72 hours for high-bleeding-risk procedures. 1

Pitfall #3: Giving Last Preoperative Dose Too Close to Surgery

Administering LMWH 12 hours before surgery leaves 34% of patients with therapeutic anticoagulation at the time of incision. 1 The last dose should be 24 hours preoperatively. 1

Pitfall #4: Bridging for Minor Procedures

For procedures where bleeding is easily controlled (dental extractions, cataract surgery, minor dermatologic procedures), continue acenocoumarol with therapeutic INR—do not interrupt or bridge. 1, 2

Practical Bridging Protocol (When Indicated)

Preoperative:

• Stop acenocoumarol 5 days before surgery 2
• Start therapeutic-dose LMWH when INR falls below 2.0 (typically 2 days after stopping acenocoumarol) 2, 4
• Give last LMWH dose 24 hours before surgery 1
• Check INR morning of surgery to confirm <1.5 2

Postoperative:

• Resume acenocoumarol 12-24 hours after surgery when hemostasis is adequate 1, 2
• For low-bleeding-risk procedures: Resume therapeutic LMWH 24 hours postoperatively 1
• For high-bleeding-risk procedures: Delay therapeutic LMWH for 48-72 hours, or use prophylactic-dose LMWH initially 1
• Continue LMWH until INR is therapeutic (≥2.0) for 24 hours 1

The Bottom Line

Bridging exists because acenocoumarol has a slow offset and onset, creating a dangerous anticoagulation gap—but modern evidence shows this gap is only clinically significant in patients with mechanical heart valves or very recent thromboembolism. 1 For the vast majority of patients, the bleeding risk of bridging outweighs any theoretical benefit. 1, 3 The decision to bridge should be based on thromboembolic risk stratification, not reflexive practice. 1