Recommended Time Window for Mechanical Thrombectomy in Acute Ischemic Stroke
Mechanical thrombectomy is strongly recommended for eligible patients with large vessel occlusion in the anterior circulation within 24 hours of symptom onset, with treatment selection criteria varying based on the specific time window. 1
Time Windows for Mechanical Thrombectomy
0-6 Hours from Symptom Onset
- Strong recommendation for thrombectomy (Level I, Evidence A) for patients with:
- Large vessel occlusion (internal carotid artery or proximal middle cerebral artery M1 segment)
- ASPECTS ≥6
- Pre-stroke mRS score of 0-1
- Age ≥18 years 1
- Patient selection in this window primarily based on non-contrast CT and CT angiography
- No advanced imaging (perfusion) required in this early window 1
6-16 Hours from Symptom Onset
- Strong recommendation (Level I, Evidence A) for thrombectomy if patients meet DAWN or DEFUSE 3 criteria 1
- Advanced imaging (CT perfusion or DW-MRI) is mandatory to identify clinical-imaging mismatch or perfusion-core mismatch 1
- Patients selected in this window can achieve favorable outcomes comparable to those treated in the early window 2, 3
16-24 Hours from Symptom Onset
- Reasonable recommendation (Level IIa, Evidence B-R) for thrombectomy if patients meet DAWN criteria 1
- Advanced imaging is essential to identify clinical-imaging mismatch 1
- Extending the window to 24 hours increases the number of patients who can benefit from thrombectomy by approximately 25-30% 3
Patient Selection Criteria
Essential Criteria Across All Time Windows
- Large vessel occlusion in anterior circulation (ICA, M1 MCA)
- ASPECTS ≥6 (indicating limited early ischemic changes)
- Pre-stroke mRS 0-1 (minimal pre-existing disability)
- Age ≥18 years 1
Additional Selection Criteria for Extended Window (6-24 Hours)
- DAWN criteria: Clinical-imaging mismatch based on NIHSS and infarct core volume
- DEFUSE 3 criteria (6-16 hours only): Perfusion-core mismatch 1
Special Considerations
Important Caveats
- Treatment beyond 24 hours is not currently recommended (Level IIa) 1
- Do not delay thrombectomy to assess response to IV thrombolysis if indicated 1
- Technical goal should be achieving modified TICI grade 2b/3 reperfusion for optimal outcomes 1
- Patients with mild deficits (NIHSS <6) may still benefit if they have ICA or M1 occlusion, though with higher risk of symptomatic hemorrhage 1
- Elderly patients (≥80 years) should not be excluded based on age alone 1
Potential Pitfalls
- Waiting for advanced imaging in the early time window (<6 hours) may unnecessarily delay treatment 1
- Excluding patients based solely on age can deprive elderly patients of significant benefits 1
- Limiting thrombectomy to only the early window (<6 hours) misses approximately 25-30% of potentially treatable patients 3
- Overreliance on strict ASPECTS cutoffs may exclude patients who could still benefit (ASPECTS <6 may still be reasonable in selected cases) 1
Implementation Considerations
- Advanced imaging increases the likelihood of good functional outcomes in extended time windows 4
- Even in resource-limited settings, extended window thrombectomy can be performed safely with adequate outcomes 5, 6
- Pragmatic approaches using ASPECTS ≥6 and CTA collateral assessment can be effective for patient selection in centers without advanced perfusion imaging 6