What is the maximum time window for intravenous thrombolysis with alteplase in acute ischemic stroke?

Explanation

## IV Thrombolysis Time Window in Acute Ischemic Stroke **Key Point:** The FDA-approved time window for intravenous alteplase (tissue plasminogen activator, tPA) in acute ischemic stroke is **4.5 hours from symptom onset**, though the standard window is 3 hours. ### Evidence-Based Time Windows | Time Window | Evidence | Recommendation | |-------------|----------|----------------| | 0–3 hours | NINDS rt-PA Stroke Study (1995) | Standard approved window; highest benefit | | 3–4.5 hours | ECASS III trial (2008) | Extended window; FDA-approved in 2009 | | > 4.5 hours | Not recommended for IV tPA | Consider mechanical thrombectomy if eligible | ### Historical Context 1. **NINDS rt-PA Stroke Study (1995):** Established the 3-hour window as the gold standard. Patients treated with IV alteplase within 3 hours had significantly better outcomes (31% absolute risk reduction in favorable outcome). 2. **ECASS III Trial (2008):** Extended the window to 4.5 hours in selected patients without contraindications. This led to FDA approval of the extended window in 2009. **High-Yield:** The 4.5-hour window applies to patients without: - Prior stroke and diabetes - Severe stroke (NIHSS > 25) - Age > 80 years - Oral anticoagulation use (regardless of INR) ### Clinical Pearl **Clinical Pearl:** "Time is brain" — every minute of ischemia results in loss of ~1.9 million neurons. The earlier thrombolysis is administered, the better the outcome. Patients treated within the first 90 minutes have the best prognosis. **Mnemonic:** **3-4-5 rule** — 3 hours (standard window), 4.5 hours (extended window), 5 minutes (door-to-needle target). ### Current Guidelines (AHA/ASA 2019) - **0–3 hours:** IV alteplase is recommended (Class I, Level of Evidence A) - **3–4.5 hours:** IV alteplase may be considered in selected patients (Class IIb, Level of Evidence B) - **> 4.5 hours:** Mechanical thrombectomy is preferred if large vessel occlusion is present and patient is within 24 hours of symptom onset (Class I, Level of Evidence A)