What is the meaning of window period in stroke?

Window Period in Stroke: Definition and Clinical Significance

The window period in stroke refers to the time frame after stroke onset during which specific therapeutic interventions can be safely and effectively administered to improve patient outcomes related to morbidity, mortality, and quality of life. 1

Intravenous Thrombolysis Window Periods

• 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

• Evidence supports extending the window period to 3-4.5 hours after stroke onset for carefully selected patients (Class I Recommendation, Level of Evidence B) 1

• The extended 3-4.5 hour window requires additional exclusion criteria compared to the 0-3 hour window:

  • Patients older than 80 years 1
  • Those taking oral anticoagulants (regardless of INR) 1
  • Those with baseline National Institutes of Health Stroke Scale score >25 1
  • Those with both a history of stroke and diabetes 1

Clinical Significance of Window Period

• Earlier treatment within the window period is associated with better outcomes - "delays in evaluation and initiation of therapy should be avoided, because the opportunity for improvement is greater with earlier treatment" 1

• The window period concept exists because the risk-benefit ratio changes over time:

  • Within the approved window periods, benefits of reperfusion outweigh risks of complications 1
  • Beyond established window periods, risk of adverse effects (particularly hemorrhagic transformation) increases significantly 2, 3

• The primary efficacy outcome in the ECASS-3 trial (modified Rankin Scale score of 0-1 at 90 days) was significantly greater with rtPA (52.4%) than with placebo (45.2%) when administered in the 3-4.5 hour window 1

Recent Developments in Window Period Extension

• Advanced imaging techniques are being used to potentially extend treatment windows beyond conventional time limits by identifying salvageable brain tissue 2, 4

• For selected patients with favorable imaging profiles, mechanical thrombectomy window periods have been extended up to 24 hours in some cases 2

• Research suggests that some patients may benefit from thrombolysis beyond the 4.5-hour window when selected using perfusion imaging or diffusion-weighted imaging-fluid-attenuated inversion recovery mismatch 5

Clinical Implications and Pitfalls

• The window period should not be viewed as an absolute cutoff but rather as a guide for optimal treatment timing 4

• Common pitfalls in window period determination:

  • Uncertain time of symptom onset (e.g., wake-up strokes) requires special consideration and may benefit from advanced imaging 2
  • Delaying treatment within the window period reduces chances of good outcomes - treatment should be initiated as early as possible 1
  • Extending treatment beyond established window periods without proper patient selection increases risk of symptomatic intracerebral hemorrhage 5, 3

• Symptomatic intracerebral hemorrhage rates increase with delayed treatment:

  • In ECASS-3, symptomatic intracerebral hemorrhage occurred in 7.9% of rtPA-treated patients vs 3.5% of placebo patients in the 3-4.5 hour window 1
  • Meta-analyses of treatment beyond 4.5 hours show increased odds of symptomatic intracerebral hemorrhage (OR 4.25) despite potential benefits in functional outcomes 5