Does a patient with a prosthetic mitral valve and an INR of 1.5 require in-hospital scheduled warfarin (coumarin) dose adjustment and bridging anticoagulation with enoxaparin (low molecular weight heparin)?

Management of Prosthetic Mitral Valve with INR 1.5

Yes, a patient with a prosthetic mechanical mitral valve and an INR of 1.5 requires in-hospital bridging anticoagulation with enoxaparin (or unfractionated heparin) while simultaneously continuing warfarin until the INR reaches therapeutic range (2.5-3.5). 1

Rationale for Bridging Therapy

Mechanical mitral valves are classified as high-risk for thromboembolism, and any period with subtherapeutic INR creates substantial risk for valve thrombosis and systemic embolism. 1 The ACC/AHA guidelines explicitly recommend bridging anticoagulation for patients with mechanical mitral valve replacement when the INR is subtherapeutic. 1

Target INR for Mechanical Mitral Valves

• The target INR for all mechanical mitral valves is 3.0 (range 2.5-3.5), which is higher than for mechanical aortic valves due to the significantly greater thromboembolism risk in the mitral position. 1
• An INR of 1.5 is substantially below the therapeutic range and requires immediate intervention. 1

Specific Bridging Protocol

Initiation of Bridging

When INR falls below 2.0 in a mechanical mitral valve patient:

• Start therapeutic-dose intravenous unfractionated heparin (UFH) or subcutaneous low-molecular-weight heparin (LMWH) immediately. 1
• For LMWH: enoxaparin 100 U/kg every 12 hours (or 1 mg/kg every 12 hours). 1
• For UFH: therapeutic dosing monitored to aPTT of 1.5-2.0 times control. 1
• Continue warfarin dosing simultaneously—do not hold warfarin. 1

Duration of Bridging

• Continue bridging anticoagulation until INR is ≥2.0 and preferably reaches the therapeutic target of 2.5-3.5. 1
• Once INR is therapeutic and stable, discontinue heparin/enoxaparin. 1

Evidence Supporting This Approach

The 2021 ACC/AHA guidelines provide Class I (Level C-LD) recommendation that patients with mechanical mitral valve replacement require bridging anticoagulation during periods when INR is subtherapeutic. 1 This is based on the substantially elevated thromboembolism risk—mechanical mitral valves have higher rates of thromboembolism (2.4% per patient-year) compared to mechanical aortic valves (1.9% per patient-year). 1

The 2008 ACC/AHA guidelines similarly state that therapeutic doses of intravenous UFH should be started when INR falls below 2.0 in high-risk patients, which includes any mechanical mitral valve replacement. 1

Contrast with Low-Risk Patients

This differs from mechanical aortic valves without risk factors, where bridging may not be necessary during brief interruptions. 1 However, mechanical mitral valves are always considered high-risk regardless of other factors. 1

Common Pitfalls to Avoid

• Do not simply increase warfarin dose and wait—the lag time for warfarin effect (3-5 days) leaves the patient unprotected. 1
• Do not use vitamin K to "reset" anticoagulation, as this creates a hypercoagulable state and increases valve thrombosis risk. 1
• Avoid subtherapeutic LMWH dosing—use full therapeutic doses (100 U/kg every 12 hours), not prophylactic doses. 1
• Monitor anti-factor Xa levels if using LMWH in patients with renal dysfunction or obesity to ensure adequate anticoagulation. 1, 2

Hospital Management Specifics

While hospitalized:

• Continue daily warfarin dosing, adjusting based on INR response. 1, 3
• Check INR daily until stable in therapeutic range. 1
• Overlap heparin/enoxaparin with warfarin for at least 24 hours after achieving therapeutic INR. 1
• Consider morning warfarin administration (10 AM) rather than evening, as this may achieve therapeutic INR faster post-operatively. 4

The PERIOP-2 trial demonstrated that in mechanical valve patients, post-operative bridging with dalteparin showed no thromboembolism events (0%) in the bridging group, supporting the safety and potential benefit of this approach. 1