What should the International Normalized Ratio (INR) be for an On-X (mechanical aortic valve)?

From the Guidelines

For an OnX valve, the recommended INR target range is 1.5-2.0 in conjunction with aspirin 81 mg daily for long-term management, with an initial target of 2.5 (range, 2.0-3.0) for the first 3 months after surgery. This recommendation is based on a single RCT 1 that compared lower- versus standard-intensity VKA therapy (with low-dose aspirin) in patients undergoing On-X AVR, which found that the lower-intensity INR group experienced significantly less major and minor bleeding, while the rates of stroke, transient ischemic attack, total neurological events, and all-cause mortality were similar between the 2 groups.

Key Considerations

• The use of warfarin with a target INR of 1.5-2.0, in combination with low-dose aspirin, is a strategy for reducing the risk of thromboembolic events while minimizing the risk of bleeding 1.
• The initial INR target of 2.5 (range, 2.0-3.0) for the first 3 months after surgery is intended to decrease the risk of thromboembolism until the prosthetic valve is fully endothelialized 1.
• Regular monitoring of INR levels is crucial to ensure that the patient's blood clotting ability remains within the target range, and to adjust the warfarin dose as needed 1.
• Patients should be aware of the potential interactions between warfarin and other medications, foods, and supplements, and should inform all healthcare providers about their mechanical valve and anticoagulation needs 1.

Management

• Patients with an OnX valve should have their INR checked regularly, typically every 2-4 weeks once stable 1.
• The warfarin dose should be adjusted based on the results of regular blood tests to maintain the INR within the target range 1.
• Low-dose aspirin (81 mg daily) should be used in conjunction with warfarin for long-term management 1.

From the Research

INR Targets for On-X Valve

The optimal international normalized ratio (INR) target for patients with an On-X mechanical aortic valve is a subject of ongoing research. Several studies have investigated the safety and efficacy of different INR ranges for these patients.

• The Prospective Randomized On-X Anticoagulation Clinical Trial (PROACT) compared the safety of less aggressive anticoagulation (INR 1.5-2.0) with standard anticoagulation (INR 2.0-3.0) after implantation of On-X aortic prostheses for patients at high risk of thromboembolic events, and found that low-dose warfarin is associated with lower major bleeding with no difference in thromboembolic events 2.
• A prospective, observational registry found that warfarin targeted at an INR of 1.8 (range 1.5-2.0) plus daily aspirin is safe and effective in patients with an On-X aortic mechanical valve, with a 57% reduction in the primary composite end point rate compared to standard-dose warfarin (INR 2.0-3.0) plus daily aspirin 3.
• A review of the current guidelines and published literature suggests that the INR goal in high-risk On-X aortic valve recipients can be managed at 1.5 to 2.5 with low-dose aspirin 3 months after valve implantation 4.
• However, a case report presents a patient who developed recurrent thromboembolic strokes despite maintaining an INR of 2.4, highlighting the need for caution when applying the recommended INR range of 1.5-2 for On-X valves, and suggesting that a higher INR range (2.5-3.5) may be necessary in some cases 5.
• A study of patients who received an On-X mechanical heart valve for pulmonary valve replacement found excellent mid-term durability with an INR range of 1.5-2.0, with no thromboembolisms or bleeding events 6.

Key Findings

• The recommended INR range for On-X valves is 1.5-2.0, but this may need to be adjusted based on individual patient risk factors and response to anticoagulation.
• Low-dose warfarin (INR 1.5-2.0) is associated with lower major bleeding and similar thromboembolic event rates compared to standard-dose warfarin (INR 2.0-3.0).
• The addition of aspirin to warfarin may be beneficial in reducing the risk of thromboembolic events.
• Higher INR ranges (2.5-3.5) may be necessary in some cases, such as patients with recurrent thromboembolic events despite adequate anticoagulation.