What is the window period for stroke treatment?

Window Period for Stroke Treatment

For intravenous thrombolysis in acute ischemic stroke, the standard treatment window is within 3 hours of symptom onset, with an extended window of 3-4.5 hours available for carefully selected patients who meet specific eligibility criteria. 1, 2

Standard Treatment Window (0-3 Hours)

• Patients eligible for rtPA within 3 hours of stroke onset should receive treatment immediately, as this represents the strongest evidence for efficacy and safety. 1, 2
• The benefit is greatest with earlier treatment—every minute counts, and delays within the window significantly reduce the opportunity for improvement. 2
• The NINDS study demonstrated robust benefit with an odds ratio of 1.9 (95% CI 1.2-2.9) for favorable outcomes when treating within 3 hours. 1
• Standard dosing is 0.9 mg/kg (maximum 90 mg), with 10% given as initial bolus and remainder infused over 1 hour. 1

Extended Window (3-4.5 Hours)

rtPA administration in the 3-4.5 hour window is a Class I Recommendation with Level B evidence, but requires additional exclusion criteria beyond the standard 3-hour protocol. 1, 2

Additional Exclusion Criteria for 3-4.5 Hour Window:

• Age >80 years 1, 2
• Baseline NIHSS score >25 1, 2
• Any patient taking oral anticoagulants (regardless of INR) 1, 2
• Combined history of both prior stroke AND diabetes mellitus 1, 2

Evidence Supporting Extended Window:

• The ECASS-3 trial showed 52.4% of rtPA-treated patients achieved modified Rankin Scale 0-1 at 90 days versus 45.2% with placebo (OR 1.34,95% CI 1.02-1.76). 1
• The benefit in the 3-4.5 hour window (OR 1.28) is numerically less than the 0-3 hour window (OR 1.9), though confidence intervals overlap. 1
• Canadian registry data (CASES) confirmed feasibility with 39.4% achieving excellent outcomes in the 3-4.5 hour group. 3

Critical Safety Considerations

Symptomatic intracranial hemorrhage risk increases with delayed treatment:

• In the 3-4.5 hour window: 7.9% with rtPA versus 3.5% with placebo (OR 2.38,95% CI 1.25-4.52) using NINDS criteria. 1
• A trend toward higher mortality exists in later treatment windows (28.4% vs 21.4%, p=0.09). 3
• Hemorrhage rates demonstrate a statistically significant rising trend with later time windows (p=0.013). 3

Beyond 4.5 Hours

• For patients presenting >4.5 hours from symptom onset, standard IV thrombolysis is not recommended without advanced imaging selection. 4
• Recent evidence suggests selected patients up to 24 hours may benefit from mechanical thrombectomy with advanced imaging (perfusion or DWI-FLAIR mismatch), but this represents a different treatment paradigm. 5, 6
• A 2025 meta-analysis showed IVT beyond 4.5 hours (without mechanical thrombectomy) increased excellent outcomes (OR 1.43) but also increased symptomatic ICH (OR 4.25) with nonsignificant mortality increase. 6

Common Pitfalls to Avoid

• Do not delay treatment to obtain "better" imaging if the patient is within the 3-hour window and meets standard criteria—time is brain, and earlier treatment yields exponentially better outcomes. 1, 2
• Do not treat patients in the 3-4.5 hour window if they meet any of the four additional exclusion criteria, even if they would qualify for the 0-3 hour window. 1
• Do not assume all anticoagulated patients are excluded from the 0-3 hour window—only those with INR >1.7 are excluded in the standard window, but ALL anticoagulated patients are excluded in the 3-4.5 hour window. 1
• Avoid administering antiplatelet or anticoagulant therapy within 24 hours after rtPA (except for DVT prophylaxis, which was permitted in ECASS-3). 1