Bridging Anticoagulation

Bridging is the use of short-acting parenteral heparin while warfarin is interrupted and not yet therapeutic, to cover the period of subtherapeutic anticoagulation. It lowers clot risk only in high-risk patients and increases bleeding, so it is limited to carefully chosen indications.

Bridging is not used for direct oral anticoagulants (short half-life, rapid return of effect), and is not routine for atrial fibrillation without a mechanical valve, where the added bleeding outweighs the benefit.

High clot risk (bridge): - Mechanical mitral valve, and mechanical aortic valve with atrial fibrillation, prior stroke or other risk factors, or any older-generation valve. - Venous thromboembolism within the last 3 months, or severe thrombophilia (antithrombin deficiency, antiphospholipid syndrome). - Stroke or systemic embolism within 3 months, or atrial fibrillation with rheumatic mitral stenosis and previous embolism.

Moderate and low risk: do not bridge (atrial fibrillation without valve disease, venous thromboembolism over 12 months ago).

Regimen for a planned procedure: - Stop warfarin 5 days before the procedure. Check INR the day before; if over 1.5, give oral vitamin K 1 to 2 mg. - Start enoxaparin 1 mg/kg subcutaneously twice daily on day 3 before surgery (about 36 hours after the last warfarin dose).

Give the last dose in the morning of the day before the procedure, at half the daily dose (about 1 mg/kg once), at least 24 hours before the procedure.

• Restart warfarin on the evening of surgery or the next day at the usual dose if bleeding is controlled.
• Restart enoxaparin 24 hours after low-bleeding-risk procedures and 48 to 72 hours after high-bleeding-risk procedures, and continue until INR is in range for 24 hours (2 consecutive days for mechanical valves).
• Unfractionated heparin infusion (inpatient, mechanical valves with kidney disease): 80 units/kg bolus then 18 units/kg/h, adjusted to aPTT 1.5 to 2.5 times control, stopped 4 to 6 hours before the procedure.

At initiation of warfarin. Heparin overlap for at least 5 days and until INR is 2.0 or more for 24 hours (venous thromboembolism).

Kidney impairment. Creatinine clearance under 30 mL/min: enoxaparin 1 mg/kg once daily, or unfractionated heparin.

Pregnancy. Weight-banded low molecular weight heparin, planned by a specialist team.

Obesity. Actual body weight dosing, with anti-Xa check over 150 kg.

Thrombocytopenia. Platelets under 50 x 10^9/L need specialist review before bridging.

Special groups. In East Africa, rheumatic mitral stenosis with embolism history is a common bridging indication, and unfractionated heparin by infusion may be the only available option.

Monitoring. Daily full blood count if bridging is longer than 5 days, platelets for heparin-induced thrombocytopenia, creatinine, wound bleeding, and INR daily when restarting warfarin.

Referral and escalation. Seek haematology and cardiology advice for mechanical valves in pregnancy, recent stroke, bleeding after bridging, and platelet fall over 50%.

Stopping. Stop heparin when INR is in range for 24 hours (2 consecutive days for mechanical valves). Do not bridge for longer than needed.