Length of treatment

Short term to medium term (up to 12 months). These include:

• mural thrombus
  • patients with mural thrombus after myocardial infarction are at greatest risk of embolization in the first 3 months, especially in the presence of a left ventricular aneurysm. Following initial heparin therapy, warfarin is recommended for 3 months to achieve an INR of 2.5 (1)
• prophylaxis versus DVT including high risk surgery
• treatment of venous thromboembolism - deep vein thrombosis (DVT) or pulmonary embolism (PE) (2)
  • anticoagulation for 1 month is inadequate treatment after an episode of VTE
  • at least 6 weeks anticoagulation is recommended after calf vein thrombosis and at least 3 months after proximal DVT or PE
  • for patients with temporary risk factors and a low risk of recurrence 3 months of treatment may be sufficient
  • For patients with idiopathic VTE or permanent risk factors at least 6 months anticoagulation is recommended
  • target INR of 2·5 is recommended for long-term oral anticoagulant (VKA) therapy for secondary prevention of VTE
  • target INR of 2·5 is recommended for patients with DVT or PE associated with antiphospholipid syndrome
    • target of 3·5 is also recommended for patients who suffer recurrence of VTE whilst on warfarin with an INR between 2·0 and 3·0
• bioprosthetic valves (2)
  • long-term warfarin not required in absence of atrial fibrillation
  • oral anticoagulants are not required for valves in the aortic position in patients in sinus rhythm, although many centres anticoagulate patients for 3–6 months after any tissue valve implant
    • patients with bioprostheses in the mitral position should receive oral anticoagulants to achieve an INR of 2.5 for the first 3 months. After 3 months, patients with atrial fibrillation should receive lifelong therapy to achieve an INR of 2.5
    • patients with bioprosthetic valves with a history of systemic embolism and those with intracardiac thrombus should also be anticoagulated to achieve an INR of 2.5
    • patients who do not require oral anticoagulants after the first 3 months may be considered for antiplatelet therapy, e.g. aspirin

Long term treatment. These include:

• recurrent venous thromboembolism
• cardiac prosthetic valve replacements
• embolic complications of atrial fibrillation and rheumatic heart disease
  • warfarin should be considered as first-line therapy in patients with atrial fibrillation and at least one risk factor (previous thromboembolism, hypertension, heart failure, abnormal left ventricular function on echocardiography) for thromboembolism. However, patients should be reviewed as the benefit/risk ratio may alter with increasing age or the development of additional illness. Low-risk patients may be treated with aspirin alone
  • risk of stroke is 3 times greater in patients with atrial fibrillation with mitral stenosis than in those without valve disease - based on its apparent effectiveness in non-randomized studies and its effect in non-rheumatic atrial fibrillation, warfarin is usually given to maintain an INR of 2.5 (1)
• dilated cardiomyopathy (1)
  • dilated cardiomyopathy is associated with a 30–50% risk of thrombus formation and a high risk of systemic embolisation. Prolonged anticoagulant therapy is recommended

Reference:

1. British Committee on Standards in Haematology. Guidelines on oral anticoagulation: third edition British Journal of Haematology 1998;101 (2); 374–387.
2. Baglin TP et al British Committee for Standards in Haematology - Guidelines on oral anticoagulation (warfarin): third edition - 2005 update British Journal of Haematology 2006; 132 (3): 277–285.