INR Targets for Mechanical Valve Anticoagulation
For mechanical aortic valve replacement (AVR) without additional risk factors, target an INR of 2.5 (range 2.0-3.0); for mechanical mitral valve replacement (MVR) or mechanical AVR with risk factors, target an INR of 3.0 (range 2.5-3.5). 1
Mechanical Aortic Valve Replacement
Standard Risk Patients (No Additional Risk Factors)
- Target INR: 2.5 (range 2.0-3.0) for bileaflet or current-generation single tilting disc valves 1
- This applies specifically to patients in sinus rhythm without atrial fibrillation, prior thromboembolism, LV dysfunction, hypercoagulable conditions, or left atrial enlargement 1
- Add aspirin 75-100 mg daily to warfarin therapy 1
High Risk Patients (With Additional Risk Factors)
- Target INR: 3.0 (range 2.5-3.5) when any of the following are present: 1
- Atrial fibrillation
- Previous thromboembolism
- Left ventricular dysfunction
- Hypercoagulable conditions
- Older-generation mechanical valves (ball-in-cage, caged disk) 1
- Add aspirin 75-100 mg daily 1
Important caveat: Recent evidence challenges the higher INR target for mechanical AVR patients with risk factors. A 2021 study found that standard-intensity anticoagulation (INR 2.5) was associated with significantly fewer bleeding events compared to higher-intensity (INR 3.0), with minimal thromboembolic events in both groups (adjusted HR for bleeding 2.52,95% CI 1.27-5.00) 2. However, current ACC/AHA guidelines still recommend the higher target 1.
Mechanical Mitral Valve Replacement
- Target INR: 3.0 (range 2.5-3.5) for all mechanical mitral valves, regardless of valve type 1
- The higher target reflects the consistently greater thromboembolic risk with mitral position valves compared to aortic position 1
- Add aspirin 75-100 mg daily 1
Special Considerations
On-X Mechanical Aortic Valve
- For On-X AVR without thromboembolic risk factors, a lower INR target of 1.5-2.0 may be reasonable starting ≥3 months after surgery, with continuation of aspirin 75-100 mg daily 1
- This is a Class 2b recommendation based on valve-specific data 1
Management of Breakthrough Events
If stroke or systemic embolism occurs while in therapeutic range: 1
- Mechanical AVR patients: Increase INR goal from 2.5 (range 2.0-3.0) to 3.0 (range 2.5-3.5) OR add aspirin 75-100 mg daily if not already prescribed 1
- Mechanical MVR patients: Increase INR goal from 3.0 (range 2.5-3.5) to 4.0 (range 3.5-4.0) OR add aspirin 75-100 mg daily 1
Critical Pitfalls to Avoid
- Never use direct oral anticoagulants (DOACs): Dabigatran is contraindicated in mechanical valve patients, and anti-Xa DOACs are not recommended 1
- Avoid excessive anticoagulation: INR >4.0 provides no additional benefit and significantly increases bleeding risk 3, 4
- Do not use antiplatelet therapy alone: Aspirin or other antiplatelet agents without warfarin do not provide adequate protection for mechanical valves 4
- Recognize position-specific risk: Mitral position valves always require higher INR targets than aortic position valves due to inherently higher thrombotic risk 1, 3