In a patient with an acute posterior‑circulation ischemic stroke and no identified cardioembolic source, should anticoagulation be started, and if a cardioembolic cause is confirmed, which oral anticoagulant and dose are recommended?

Anticoagulation for Posterior Circulation Stroke

For acute posterior circulation ischemic stroke without a cardioembolic source, do not start anticoagulation—use aspirin 160-325 mg within 48 hours instead; if atrial fibrillation or another cardioembolic source is confirmed, initiate a direct oral anticoagulant (DOAC) at timing determined by stroke severity (1-14 days), strongly preferring DOACs over warfarin. 1, 2

Non-Cardioembolic Posterior Circulation Stroke

Anticoagulation is not recommended for patients with non-cardioembolic ischemic stroke, including posterior circulation strokes without an identified cardiac source. 1

• Start aspirin 160-325 mg daily within 48 hours of symptom onset after CT/MRI excludes hemorrhage to reduce stroke mortality and morbidity. 1, 3
• The routine use of anticoagulation (unfractionated heparin, LMWH, or warfarin) in unselected patients following ischemic stroke is explicitly not recommended due to increased hemorrhagic transformation risk without net benefit. 1
• Long-term antiplatelet therapy (aspirin, clopidogrel, or aspirin/extended-release dipyridamole) is recommended over anticoagulation for secondary prevention. 1

Cardioembolic Posterior Circulation Stroke (Including Atrial Fibrillation)

Critical Timing Principle

Never start any anticoagulant within 48 hours of acute stroke onset—this significantly increases symptomatic intracranial hemorrhage without benefit. 1, 2, 3

Bridging Therapy: Explicitly Contraindicated

• Do not use heparin or LMWH as "bridging" therapy during the acute stroke phase, as parenteral anticoagulation increases symptomatic intracranial hemorrhage without reducing recurrent ischemic events. 2, 3, 4, 5
• Start aspirin 160-325 mg immediately and continue until therapeutic oral anticoagulation is achieved. 1, 4

Timing Algorithm Based on Stroke Severity

The timing of DOAC initiation depends on stroke severity using the NIHSS score and requires mandatory repeat brain imaging before starting anticoagulation to exclude hemorrhagic transformation: 2, 3

• Transient Ischemic Attack (TIA): Start DOAC at 1 day after confirming no hemorrhage on imaging. 2, 3
• Mild stroke (NIHSS <8): Start DOAC after 3 days, with repeat brain imaging at day 6 before initiation. 2, 3
• Moderate stroke (NIHSS 8-15): Start DOAC after 6-8 days, with repeat brain imaging at day 6. 2, 3
• Severe stroke (NIHSS ≥16) or large territorial infarct: Start DOAC after 12-14 days, with repeat brain imaging at day 12. 2, 3

Choice of Anticoagulant

Direct oral anticoagulants (DOACs) are strongly preferred over warfarin for AF-related stroke, as they reduce intracranial hemorrhage risk by approximately 56% compared to warfarin. 1, 2, 3, 4

• Dabigatran 150 mg twice daily is specifically suggested over adjusted-dose warfarin (target INR 2.0-3.0). 1, 4
• Alternative DOACs include rivaroxaban, apixaban, or edoxaban at standard AF dosing. 1
• Use reduced DOAC doses only when patients meet specific DOAC-specific criteria (renal impairment, age, weight); otherwise, standard dosing is required to prevent underdosing and avoidable thromboembolic events. 1
• Dabigatran is contraindicated in severe renal impairment; use alternative DOAC or warfarin in this setting. 1, 4

Imaging Requirements

• Always obtain brain imaging (CT or MRI) before initiating anticoagulation to exclude hemorrhage. 2, 3
• Repeat imaging is mandatory for moderate-to-severe strokes to detect hemorrhagic transformation before starting DOACs. 2, 3
• If symptomatic hemorrhagic transformation occurs, delay anticoagulation beyond 14 days and reassess with repeat imaging. 4

VTE Prophylaxis During Immobilization

For immobilized patients, start prophylactic-dose LMWH or intermittent pneumatic compression devices beginning 2-4 days post-stroke to prevent deep vein thrombosis. 1, 3, 4

• Do not use routine antiembolic stockings, as they are not recommended. 1, 3
• This prophylactic anticoagulation is distinct from therapeutic anticoagulation and can be started earlier. 3

Common Pitfalls to Avoid

• Never combine aspirin with long-term anticoagulation after the transition period unless specific indications exist (e.g., recent ACS or PCI), as this increases bleeding risk without proven benefit for stroke prevention. 1, 4
• Never switch between anticoagulants without clear indication in patients who experience recurrent stroke on therapy; instead, assess adherence, dosing, and non-cardioembolic causes first. 1
• Do not delay workup for cardioembolic sources—perform echocardiography and prolonged cardiac monitoring promptly, as the risk of recurrent stroke is highest in the first two weeks (8-10% cumulative risk). 2, 6
• Large infarct size predicts higher risk of both hemorrhagic transformation and recurrent ischemia, supporting delayed anticoagulation initiation toward the 12-14 day window. 2, 5