Recommended INR for Mechanical Aortic Valve
For patients with a mechanical aortic valve without additional risk factors, target an INR of 2.5 (range 2.0-3.0), and add aspirin 75-100 mg daily. 1, 2
Standard Risk Patients (No Additional Risk Factors)
Target INR: 2.5 (range 2.0-3.0) for current-generation bileaflet or single tilting disk mechanical aortic valves in patients without additional thromboembolic risk factors 1
This target provides an optimal balance between preventing thromboembolism (0.53% per patient-year) and minimizing bleeding complications 1
Randomized trials comparing moderate-intensity (INR 2.0-3.0) versus high-intensity (INR 3.0-4.5) anticoagulation showed no difference in embolic events but significantly reduced bleeding with the moderate-intensity regimen 1
Avoid INR >4.0, as adverse events increase significantly above this threshold without additional therapeutic benefit 1, 2
High Risk Patients (With Additional Risk Factors)
Increase the INR target to 3.0 (range 2.5-3.5) if any of the following risk factors are present: 1, 2
- Atrial fibrillation
- Prior thromboembolism
- Hypercoagulable state
- Severe left ventricular dysfunction
- Older-generation prosthesis (e.g., ball-in-cage, caged disk)
Important Caveat on Higher Intensity Anticoagulation
Recent real-world data challenges the higher INR target for high-risk patients. A 2021 study found that patients with mechanical AVR and additional risk factors who received higher-intensity anticoagulation (INR goal 3.0) had significantly increased bleeding (adjusted HR 2.52) without reduction in thromboembolic events compared to standard-intensity (INR goal 2.5) 3. However, current ACC/AHA guidelines still recommend INR 3.0 (range 2.5-3.5) for high-risk patients 1, and this remains the standard of care until guidelines are updated.
Aspirin Therapy (Essential for All Patients)
Add aspirin 75-100 mg daily to warfarin therapy for all patients with mechanical aortic valves 1, 2
Combined warfarin plus aspirin reduces major embolism or death from 8.5% to 1.9% per patient-year and stroke from 4.2% to 1.3% per patient-year 2
This combination modestly increases bleeding risk but provides net clinical benefit 1
Critical Management Principles
Specify a single INR target value (e.g., 2.5) rather than just stating a range, as this reduces the likelihood of patients consistently running near the boundaries 1, 2
INR fluctuations are associated with increased complications; consistent monitoring and patient education are essential 1
Lifelong vitamin K antagonist (VKA) therapy is mandatory for all mechanical valves—direct oral anticoagulants (DOACs) are not approved and should never be used 1
Special Consideration: On-X Valve
For the specific On-X mechanical aortic valve, lower INR targets (1.5-2.5) with aspirin have been studied and may be considered after 3 months post-implantation, though this represents a deviation from standard bileaflet valve management 4, 5. The PROACT trial demonstrated safety of INR 1.5-2.0 with 81 mg aspirin in On-X aortic valves, with significantly lower bleeding and similar thromboembolic rates 5.