Warfarin for Mechanical Valve and Atrial Fibrillation
For patients with atrial fibrillation and a mechanical heart valve, warfarin is the only recommended anticoagulant, with a target INR that depends on valve type and location. 1
Warfarin is Mandatory - DOACs are Contraindicated
Direct oral anticoagulants (DOACs) including dabigatran, rivaroxaban, apixaban, and edoxaban are absolutely contraindicated in patients with mechanical heart valves. 1 This is a Class III: Harm recommendation from the ACC/AHA/HRS guidelines.
The RE-ALIGN trial demonstrated that dabigatran in patients with mechanical valves resulted in increased thromboembolic events (5% stroke rate vs 0% with warfarin) and major bleeding complications (4% vs 2%), leading to premature trial termination. 2
The presence of atrial fibrillation does not change this recommendation - warfarin remains the only option regardless of AF pattern (paroxysmal, persistent, or permanent). 1
Target INR Based on Valve Type and Position
For bileaflet mechanical valves in the aortic position:
- Target INR of 2.5 (range 2.0-3.0) if the patient has no additional risk factors for thromboembolism. 1, 3, 4
For mechanical valves requiring higher intensity anticoagulation:
- Target INR of 3.0 (range 2.5-3.5) for: 1, 4
- Tilting disk valves in any position
- Bileaflet mechanical valves in the mitral position
- Bileaflet valves in the aortic position with additional risk factors (atrial fibrillation, previous thromboembolism, left ventricular dysfunction, or hypercoagulable conditions)
- Older-generation mechanical valves (caged ball or caged disk valves)
The presence of atrial fibrillation is considered an additional risk factor that may warrant the higher INR target of 2.5-3.5, particularly for aortic valve prostheses. 1
INR Monitoring Requirements
Check INR at least weekly during warfarin initiation. 1
Once stable anticoagulation is achieved (INR consistently in therapeutic range), check INR at least monthly. 1, 3
Patients with mechanical valves require meticulous INR monitoring, as fluctuations in INR are associated with increased complications. 1
Anticoagulation clinics with dedicated pharmacists or nurses result in lower complication rates compared to standard care and are cost-effective. 1
Bridging for Procedures
When warfarin must be interrupted for procedures, bridging therapy with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH) is mandatory for patients with mechanical valves and AF. 1 This is a Class I recommendation.
The decision about bridging must balance stroke risk (which is high with mechanical valves) against bleeding risk from the procedure. 1
Special Consideration: End-Stage Renal Disease
For patients with mechanical valves, atrial fibrillation, AND end-stage renal disease or dialysis, warfarin remains the only option. 1, 5
Target INR remains 2.0-3.0 for most mechanical valves, though these patients have both increased thromboembolism and bleeding risk requiring particularly careful monitoring. 5
DOACs including apixaban are not adequately studied and should not be used in this population with mechanical valves. 1, 5
Critical Pitfalls to Avoid
Never use a DOAC in a patient with a mechanical valve, even if they have atrial fibrillation. The combination of mechanical valve + AF does not make DOACs acceptable - it remains an absolute contraindication. 1, 2
Do not use the CHA₂DS₂-VASc score to determine anticoagulation need in mechanical valve patients - the mechanical valve itself mandates anticoagulation regardless of score. 1
Avoid INR values consistently at the lower boundary of the therapeutic range, as this increases thromboembolic risk. Aim for the specific target INR value (2.5 or 3.0 depending on valve type). 1
Bleeding risk increases exponentially when INR exceeds 4.0, and becomes clinically unacceptable above 5.0. 6
Patients over age 75 with mechanical valves still require full-intensity anticoagulation based on valve type, unlike nonvalvular AF where lower targets might be considered. 1