Intended for healthcare professionals

Practice Therapeutics

Warfarin in patients with mechanical heart valves

BMJ 2020; 371 doi: (Published 15 October 2020) Cite this as: BMJ 2020;371:m3956
  1. Fiona Catterall, ST3 medicine1,
  2. Paul RJ Ames, consultant haematologist2,
  3. Chris Isles, consultant physician1
  1. 1Medical Unit and 2Department of Haematology, Dumfries and Galloway Royal Infirmary, Dumfries, UK
  1. Correspondence to F Catterall Fiona.catterall{at}

What you need to know

  • Patients with mechanical heart valves require lifelong anticoagulation with warfarin to prevent thromboembolism

  • Do not prescribe direct oral anticoagulants as their safety in patients with mechanical heart valves is not established

  • Low dose aspirin can be added to warfarin in patients with higher risk of thromboembolic events, though the risk of bleeding is increased and closer monitoring of the dose of warfarin will be required

A 55 year old woman with severe aortic stenosis underwent valve replacement with a mechanical valve. She has been started on warfarin and is maintaining an international normalised ratio (INR) within the target range of 2.0-3.0. She finds monitoring INR levels cumbersome. She has heard about newer direct oral anticoagulants and asks if she can switch to one of these.

Heart valve replacement

Valve replacement or repair is the definitive treatment in those with severe valvular heart disease. The choice of valve depends on valve durability, the need for antithrombotic therapy, and patient preferences.12 Mechanical heart valves are preferred in patients under 65.3 Bioprosthetic valves do not require lifelong anticoagulation but have a greater rate of primary failure and are associated with a higher reoperation rate. They last only 10 to 15 years compared with 20 to 30 years for mechanical heart valves.3

Warfarin is an anticoagulant prescribed to patients with mechanical heart valves. Patients with mechanical heart valves have a risk of thrombosis on the valve and subsequent embolism. Blood flows at high shear stress around the valve, which activates platelets and local coagulation. Latest European, US, and National Institute of Health and Care Excellence (NICE) guidelines recommend lifelong treatment with warfarin to prevent this.1245

What is warfarin?

Warfarin is a vitamin K antagonist. Other drugs in this group are acenocoumarol and dicoumarol. Warfarin inhibits the synthesis of the vitamin K dependent …

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