Apixaban or Warfarin in Patients With On-X Mechanical Aortic Valve

Quick Takes

  • Patients with On-X mechanical aortic valve replacement were randomized to receive apixaban or warfarin therapy.
  • Patients randomized to apixaban therapy had higher rates of thromboembolism than those receiving warfarin.
  • The rate of major bleeding was numerically, but not statistically, lower in the patients treated with apixaban as compared to warfarin.

Study Questions:

Can patients with an On-X mechanical aortic valve replacement be safely anticoagulated with apixaban as compared to warfarin?


The PROACT Xa trial investigators randomized patients with On-X mechanical aortic valve replacement ≥3 months post-implantation to receive either apixaban 5 mg twice daily or warfarin (target international normalized ratio 2.0-3.0). The primary efficacy outcome was the composite of valve thrombosis or valve-related thromboembolism. The primary safety outcome was major bleeding. The study was designed to explore noninferiority of apixaban versus warfarin.


The trial was stopped after 863 patients had been randomized owing to an excess of thromboembolic events in the apixaban group. Aspirin was used by most patients (94%) in addition to anticoagulation. The primary endpoint occurred in 4.2%/patient-years (95% confidence interval [CI], 2.3-6.0) in the apixaban-treated cohort and in 1.3%/patient-years (95% CI, 0.3-2.3) in the warfarin cohort (hazard ratio [HR], 2.6; 95% CI, 1.0-6.7). Major bleeding rates were 3.6%/patient-years in the apixaban cohort and 4.5%/patient-years in the warfarin cohort (HR, 0.6; 95% CI, 0.3-1.3).


The authors concluded that apixaban is less effective than warfarin for the prevention of valve thrombosis or thromboembolism in patients with On-X mechanical aortic valve replacement.


Following the results of the RE-ALIGN trial comparing dabigatran to warfarin in patients with mechanical aortic valve replacement, warfarin has been the standard of care for thrombosis prevention in anyone with a mechanical valve replacement. Recently, the On-X valve was shown to be less thrombogenic and lower-intensity warfarin can be used when this valve is placed in the aortic position. The PROACT Xa investigators hoped to demonstrate noninferiority with apixaban as compared to warfarin given the better thrombosis profile of the On-X valve and the presumed efficacy and safety profile of apixaban. However, this study demonstrates that patients with mechanical valves still require warfarin therapy.

Clinical Topics: Anticoagulation Management, Cardiac Surgery, Invasive Cardiovascular Angiography and Intervention, Prevention, Valvular Heart Disease, Cardiac Surgery and Arrhythmias, Cardiac Surgery and VHD, Novel Agents, Interventions and Structural Heart Disease

Keywords: Anticoagulants, Aspirin, Cardiac Surgical Procedures, Dabigatran, Heart Valve Diseases, Hemorrhage, International Normalized Ratio, Secondary Prevention, Thromboembolism, Thrombosis, Vascular Diseases, Warfarin

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