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Thromboembolism in atrial fibrillation (primary prevention)

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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All patients with atrial fibrillation should be considered for anticoagulation. There is often a balance to be reached between the benefits of reducing the incidence of stroke and the possible complications of anticoagulation in old and infirm patients. Clearly the assessment of thromboembolic risk factors is important in making a sensible therapeutic decision.

An overview of five trials of warfarin in atrial fibrillation has shown that anticoagulation:

  • reduced stroke by 68% compared to placebo
  • reduced death by 33% compared to placebo

The target INR to maintain during anticoagulation should be between 2-3 (1).

Aspirin is a convenient drug for patients who cannot be anticoagulated. Aspirin is approximately half as effective as warfarin for the primary prevention of strokes. Aspirin is probably inadequate therapy for patients with the following risk factors:

  • heart failure or left ventricular dysfunction
  • uncontrolled hypertension
  • females aged >75 years

The CHADS2 (2) scoring system and the CHA2DS2-VASc (3) score have subsequently been developed to identify patients with atrial fibrillation who require aspirin or oral anticoagulation therapy (see linked items).


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