## Thrombolysis Time Window in Acute Ischemic Stroke **Key Point:** The maximum time window for intravenous thrombolysis with alteplase (rt-PA) in acute ischemic stroke is **4.5 hours from symptom onset**. This extended window (beyond the original 3-hour window from NINDS rt-PA Stroke Study) is supported by the ECASS-3 trial and is now the standard of care in most international guidelines. ### Timeline of Thrombolysis Evidence | Trial/Guideline | Year | Time Window | Population | Key Finding | | --- | --- | --- | --- | --- | | NINDS rt-PA Stroke Study | 1995 | 0–3 hours | All ischemic stroke | Benefit at 3 hours; increased ICH risk | | ECASS-3 | 2008 | 3–4.5 hours | Selected patients (no major deficit) | Benefit extends to 4.5 hours | | Current AHA/ASA Guidelines | 2019 | 0–4.5 hours | Standard recommendation | 4.5 hours is maximum for IV thrombolysis | | EXTEND-IA, DAWN, DEFUSE-3 | 2017–2018 | Up to 24 hours | Thrombectomy-eligible patients | Mechanical thrombectomy window extended | ### Critical Time Windows in Acute Stroke Management **High-Yield:** - **0–4.5 hours:** IV thrombolysis (alteplase) is indicated if no contraindications - **0–24 hours:** Mechanical thrombectomy for large vessel occlusion (LVO) with salvageable penumbra - **First 3 hours:** Optimal window for best outcomes; "time is brain" - **Beyond 4.5 hours:** IV thrombolysis contraindicated; consider thrombectomy if LVO and salvageable tissue on imaging **Warning:** The 4.5-hour window applies to IV thrombolysis only. Mechanical thrombectomy has a much longer window (up to 24 hours) if there is evidence of salvageable brain tissue on perfusion imaging. **Clinical Pearl:** Patients presenting between 3–4.5 hours should be carefully selected: those with mild-to-moderate deficits and no major early infarct signs on CT are more likely to benefit. Patients with severe deficits or large infarcts on imaging in this window have higher risk of hemorrhagic transformation. **Mnemonic:** **THROMBOLYSIS WINDOW = 4.5 HOURS** — Remember: "4.5 is the maximum; beyond that, think thrombectomy." 
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