What is the target International Normalized Ratio (INR) range for patients with an Onyx valve?

Target INR Range for Patients with an Onyx Valve

For patients with an On-X mechanical aortic valve without thromboembolic risk factors, a target INR of 1.5-2.0 plus aspirin 75-100 mg daily may be used starting 3 months after surgery, while patients with mitral On-X valves or those with risk factors require higher INR targets. 1

INR Targets Based on Valve Position and Risk Factors

Aortic Position (On-X Valve)

• Without thromboembolic risk factors:

  • First 3 months post-surgery: INR 2.5 (range 2.0-3.0) 1
  • After 3 months: INR 1.5-2.0 plus aspirin 75-100 mg daily 1

• With thromboembolic risk factors:

  • INR 3.0 (range 2.5-3.5) 1
  • Risk factors include: atrial fibrillation, previous thromboembolism, hypercoagulable state, and severe LV dysfunction 1

Mitral Position (On-X Valve)

• INR 3.0 (range 2.5-3.5) 1
• Higher target needed due to increased thromboembolism risk in mitral position compared to aortic position 1

Evidence Quality and Considerations

The 2021 ACC/AHA guidelines provide clear recommendations for On-X valves specifically, noting that the lower INR target for aortic position is based on clinical evidence showing similar thromboembolic protection with reduced bleeding risk 1. However, this approach requires careful patient selection and monitoring.

Recent evidence from the PROACT registry (2024) supports the safety of lower INR targets (1.8, range 1.5-2.0) plus aspirin for On-X aortic valves, showing a 57% reduction in the composite endpoint of thromboembolism, valve thrombosis, and major bleeding compared to standard anticoagulation 2.

Important Caveats and Monitoring

• Direct oral anticoagulants (DOACs) are contraindicated for all mechanical valves, including On-X valves 1, 3

  • A 2023 study of apixaban in On-X aortic valves was stopped early due to excess thromboembolic events 3

• Anticoagulation monitoring:

  • Regular INR monitoring is essential
  • Specify a single INR target rather than just a range to avoid consistently being at the lower or upper boundary 1
  • INR fluctuations increase complication risk 1

• If thromboembolic events occur despite therapeutic INR:

  • For aortic valves: Consider increasing INR goal from 2.5 to 3.0 or adding aspirin 1
  • For mitral valves: Consider increasing INR goal from 3.0 to 4.0 or adding aspirin 1

Antiplatelet Therapy

• Low-dose aspirin (75-100 mg daily) is recommended in addition to warfarin for On-X aortic valves with the lower INR target 1
• For patients with standard INR targets, adding aspirin may be reasonable if there are additional indications for antiplatelet therapy 1
• Caution is needed when combining higher INR targets (>3.0) with aspirin due to increased bleeding risk 4

The evidence strongly supports lifelong anticoagulation with vitamin K antagonists for all mechanical valves, with the specific INR target determined by valve position, valve type, and patient risk factors.