When to start anticoagulation (blood thinner) therapy in a stroke patient?

Timing of Anticoagulation After Ischemic Stroke

In stroke patients with atrial fibrillation, initiate oral anticoagulation immediately for TIA, within 2-14 days for low-risk strokes, and delay beyond 14 days for high-risk strokes with hemorrhagic transformation potential.

Primary Decision Framework Based on Clinical Scenario

For TIA with Atrial Fibrillation

• Start anticoagulation immediately after the index event to reduce recurrent stroke risk 1
• Direct oral anticoagulants (DOACs) are preferred over warfarin: apixaban, dabigatran, edoxaban, or rivaroxaban 1

For Ischemic Stroke with Atrial Fibrillation - Risk Stratification Required

Low Risk for Hemorrhagic Conversion:

• Initiate anticoagulation 2-14 days after the index event 1
• Low-risk features include: small infarct size, no hemorrhage on imaging, lower NIHSS scores 2

High Risk for Hemorrhagic Conversion:

• Delay anticoagulation beyond 14 days to reduce intracranial hemorrhage risk 1
• High-risk features include: large ischemic lesions, cerebral microbleeds, thrombolytic therapy use, presence of hemorrhagic transformation 2

Hemorrhagic Transformation-Specific Timing

If Hemorrhagic Transformation Present on Imaging:

Lower-Grade (HI1 - small petechiae):

• Initiate antiplatelet therapy within 24-48 hours after confirming no progression on follow-up imaging 3
• For anticoagulation in AF patients, can consider earlier initiation (1-2 weeks) if small infarct burden 3

Higher-Grade (HI2, PH1, PH2 - confluent petechiae or parenchymal hemorrhage):

• Delay anticoagulation for 7-10 days minimum 3
• Confirm no expansion of hemorrhage before restarting 3
• For AF patients, generally initiate within 1-2 weeks after stroke onset once stabilized 3

Anticoagulant Selection Algorithm

First-Line: Direct Oral Anticoagulants (DOACs)

• Preferred over warfarin for nonvalvular AF 1
• Options: apixaban, dabigatran, edoxaban, or rivaroxaban 1
• Advantage: Lower intracranial hemorrhage risk compared to warfarin 4

Warfarin Indications (DOACs Contraindicated):

• Moderate to severe mitral stenosis 1
• Mechanical heart valves 1
• End-stage renal disease or dialysis (warfarin or dose-adjusted apixaban) 1
• Inability to maintain therapeutic INR with warfarin switches to DOACs 1

Critical Timing Pitfalls to Avoid

Do NOT initiate parenteral anticoagulation within 48 hours:

• Associated with increased hemorrhagic transformation risk 2
• Not recommended in acute stroke period 2

Do NOT routinely start oral anticoagulation within 48 hours:

• DOAC initiation within 2 days associated with 5% hemorrhagic transformation rate 2
• Insufficient safety data for routine early initiation 2

Do NOT use antiplatelets if anticoagulation is indicated:

• Patients suitable for anticoagulation should not receive antiplatelets for secondary stroke prevention 1

Special Cardiac Conditions Requiring Anticoagulation

Valvular Heart Disease:

• Mechanical mitral valve: Warfarin (INR 2.5-3.5) plus aspirin 75-100 mg daily 1
• Bioprosthetic valves: Long-term antiplatelet therapy beyond 3-6 months post-procedure (if no other anticoagulation indication) 1

Left Ventricular or Atrial Thrombus:

• Anticoagulation for at least 3 months 1
• Vitamin K antagonists recommended for left atrial/appendage thrombus with cardiomyopathy 1

Monitoring Strategy

• Confirm absence of hemorrhagic transformation on neuroimaging before initiating anticoagulation 3
• Repeat imaging at 7-10 days if higher-grade hemorrhagic transformation present 3
• Balance thromboembolism risk against hemorrhage risk based on infarct size and imaging features 2