Window Period in Stroke: Definition and Clinical Significance

Intravenous Thrombolysis Window Periods

The American Heart Association recommends that the traditional window period for intravenous recombinant tissue plasminogen activator (rtPA) administration is within 3 hours of stroke symptom onset, which has been the standard treatment timeframe with established efficacy and safety 1, 2, 3
Evidence supports extending the window period to 3-4.5 hours after stroke onset for carefully selected patients, with a Class I Recommendation and Level of Evidence B 1, 2, 3
The extended 3-4.5 hour window requires additional exclusion criteria, including patients older than 80 years, those taking oral anticoagulants, those with baseline National Institutes of Health Stroke Scale score >25, and those with both a history of stroke and diabetes 2, 4, 5

Earlier treatment within the window period is associated with better outcomes, with the American College of Cardiology stating that "delays in evaluation and initiation of therapy should be avoided, because the opportunity for improvement is greater with earlier treatment" 2
The window period concept exists because the risk-benefit ratio changes over time, with benefits of reperfusion outweighing risks of complications within the approved window periods 1, 3
The primary efficacy outcome in the ECASS-3 trial was significantly greater with rtPA (52.4%) than with placebo (45.2%) when administered in the 3-4.5 hour window, according to the American Heart Association 3, 4

Delaying treatment within the window period reduces chances of good outcomes, with the American College of Cardiology recommending that treatment should be initiated as early as possible 1, 2
Symptomatic intracerebral hemorrhage rates increase with delayed treatment, with a rate of 7.9% in rtPA-treated patients vs 3.5% of placebo patients in the 3-4.5 hour window, according to the American Heart Association 5