How should nicoumalone be stopped and bridged with heparin or low‑molecular‑weight heparin in a patient with a mechanical mitral valve replacement (target INR 2.5‑3.5) undergoing elective non‑cardiac surgery?

Bridging Anticoagulation for Mechanical Mitral Valve Replacement During Elective Non-Cardiac Surgery

For a patient with a mechanical mitral valve replacement (target INR 2.5-3.5) undergoing elective non-cardiac surgery, bridging anticoagulation with therapeutic-dose heparin or LMWH is reasonable when the INR is subtherapeutic, balancing the high thrombotic risk of mitral prostheses against bleeding risk. 1

Risk Stratification and Bridging Decision

Mechanical mitral valve replacement is classified as high-risk for thromboembolism, warranting bridging anticoagulation during the perioperative period when INR is subtherapeutic. 1

High-Risk Features Supporting Bridging:

• Any mechanical mitral valve replacement automatically qualifies as high-risk, regardless of other factors 1
• Additional risk factors that further increase thrombotic risk include: atrial fibrillation, previous thromboembolism within 3 months, hypercoagulable state, older-generation valves (ball-in-cage, tilting-disc), and severe left ventricular dysfunction 1
• The annual thromboembolic risk for mechanical mitral valves (0.9%) is nearly double that of mechanical aortic valves (0.5%) 2

Preoperative Management Protocol

Stopping Nicoumalone:

• Stop nicoumalone 48-72 hours before surgery to allow INR to fall below 1.5 1
• Check INR 1-2 days before surgery to confirm it is approaching the safe range for surgery 1

Initiating Bridging Anticoagulation:

• Start therapeutic-dose intravenous unfractionated heparin (UFH) when INR falls below 2.0, typically 48 hours before surgery 1
• Stop UFH 4-6 hours before the procedure to minimize bleeding risk 1

Alternative LMWH Bridging:

• Therapeutic-dose subcutaneous LMWH (100 IU/kg every 12 hours or enoxaparin 1 mg/kg twice daily) may be considered as an alternative to UFH 1
• The last dose of LMWH should be given 24 hours before surgery (omit the morning dose on the day before surgery) 1
• LMWH offers the advantage of outpatient management and no need for aPTT monitoring, though it carries a modestly higher bleeding risk than UFH in some studies 3, 4

Postoperative Management Protocol

Resuming Anticoagulation:

• Restart therapeutic-dose UFH or LMWH as early after surgery as bleeding stability allows, typically within 24 hours 1
• Continue bridging anticoagulation until INR is therapeutic (≥2.5) for two consecutive days 1, 3
• Restart nicoumalone within 24 hours after surgery, on the evening of the operative day or the next morning, depending on bleeding risk 1

Monitoring:

• Check INR daily during the bridging period until therapeutic range is achieved 3, 4
• The mean time to achieve therapeutic INR with bridging is approximately 8-9 days postoperatively 3, 4, 5

Evidence Quality and Nuances

Supporting Evidence for Bridging:

• The 2008 ACC/AHA guidelines provide Class I, Level B evidence recommending therapeutic UFH bridging for mechanical mitral valves 1
• The 2021 ACC/AHA guidelines downgraded this to Class IIa, Level C-LD, reflecting evolving evidence but still supporting bridging on an individualized basis 1
• The PERIOP-2 trial showed no thromboembolic events in mechanical valve patients (9% mitral, 11.7% aortic) with or without postoperative bridging, though all received preoperative bridging 1

LMWH vs UFH Considerations:

• Large observational studies demonstrate LMWH is effective and safe after mechanical valve replacement, with thromboembolic rates of 1% and major bleeding rates of 4.1% 4
• One comparative study found LMWH associated with higher bleeding events (9.28% vs 1.67%) but significantly shorter hospital stays and faster INR stabilization 3
• Prophylactic-dose LMWH (rather than therapeutic-dose) for periprocedural bridging showed very low event rates (0% thromboembolism, 1.3% major bleeding) in one Swedish registry study, though this approach is not guideline-recommended 6

Critical Pitfalls to Avoid

• Do not use prophylactic-dose heparin or LMWH for bridging mechanical mitral valves—therapeutic doses are required 1
• Do not give high-dose vitamin K to reverse anticoagulation for elective surgery, as this creates a hypercoagulable state and makes re-anticoagulation difficult 1
• Do not restart bridging anticoagulation too early postoperatively if there is ongoing bleeding or high bleeding risk from the surgical site 1
• Do not discontinue bridging anticoagulation before INR is stably therapeutic (≥2.5) for at least two consecutive measurements 1

Target INR for Mechanical Mitral Valve

• The long-term target INR for mechanical mitral valve replacement is 3.0 (range 2.5-3.5), which is higher than for mechanical aortic valves 1, 2
• Low-dose aspirin 75-100 mg daily should be added to warfarin therapy for all mechanical mitral valves 1, 2