Oral anticoagulants as secondary prevention of stroke or transient ischaemic attack
The recurrent stroke risk in patients with atrial fibrillation is approximately 15% per year. Atrial fibrillation becomes more prevalent with age, and is a major cause of severe stroke. The evidence is strong that anticoagulation is better than antiplatelet therapy for long-term secondary prevention of ischaemic stroke in patients with atrial fibrillation—it reduces the incidence of further events by at least 66% per year. See advice on using anticoagulants in patients with atrial fibrillation.
Atrial fibrillation is the most common source of cardiogenic embolism, but other sources should be considered—these include mural thrombus after a myocardial infarct, thrombi associated with cardiomyopathy and prosthetic cardiac valves, and rare causes (eg nonbacterial thrombotic [marantic] endocarditis). If identified, these non–atrial fibrillation sources of cardiogenic embolism should be treated with warfarin—evidence is lacking or insufficient to support using a direct-acting oral anticoagulant (DOAC).
In patients without atrial fibrillation or another source of cardiogenic embolism, the use of warfarin is not recommended. It causes harm due to major bleeding complications. Trials were underway at the time of writing to compare dabigatran with aspirin in patients with embolic stroke of unknown source.
The best time to start anticoagulation after stroke is not known. The Stroke Foundation guidelines1 recommend starting anticoagulation immediately after a TIA or minor stroke, after 5 days for a moderate stroke, and after 10 days for a severe stroke. If anticoagulation is delayed, an antiplatelet drug should be used in the interim but stopped when anticoagulation is effective.
If a patient has an ischaemic stroke while already taking an anticoagulant, consult the original prescriber if possible. Common causes of stroke in patients taking an anticoagulant are poor international normalised ratio (INR) control in patients taking warfarin, or incorrect dose of a DOAC.