Can mechanical thrombectomy (MT) be performed beyond 24 hours in patients with acute ischemic stroke?

Mechanical Thrombectomy Beyond 24 Hours in Acute Ischemic Stroke

Mechanical thrombectomy can be performed up to 24 hours after symptom onset in selected patients with acute ischemic stroke who have evidence of salvageable brain tissue based on advanced imaging criteria. 1

Patient Selection Criteria for Late Window Thrombectomy

Mechanical thrombectomy is recommended in two distinct time windows:

1. Early window (0-6 hours):

   • Age ≥18 years
   • Pre-stroke mRS score of 0-1
   • Causative occlusion of internal carotid artery or MCA (M1)
   • NIHSS score ≥6
   • ASPECTS ≥6
   • Treatment can be initiated (groin puncture) within 6 hours 1

2. Extended window (6-24 hours):

   • Patients with large vessel occlusion (LVO) in the anterior circulation
   • Must have evidence of salvageable tissue using one of these criteria:
     • Clinical-imaging mismatch (DAWN trial criteria): Combination of NIHSS and small core infarct on CTP or DW-MRI 1
     • Perfusion-core mismatch (DEFUSE 3 trial criteria): Perfusion imaging showing salvageable penumbra 1

Advanced Imaging Requirements

For patients presenting between 6-24 hours, advanced imaging is mandatory:

• CT perfusion (CTP)
• Diffusion-weighted MRI (DW-MRI)
• MRI perfusion (with or without) 1

The imaging must show a "sizable mismatch" between the ischemic core and either:

• Clinical deficits (clinical-imaging mismatch)
• Area of hypoperfusion (perfusion-imaging mismatch) 1

Evidence Supporting Extended Window Thrombectomy

The extended time window is supported by two landmark trials:

1. DAWN trial:

   • Included patients between 6-24 hours from last known normal
   • Showed 49% functional independence in treatment group vs 13% in control
   • Demonstrated 33% absolute difference in good outcomes
   • Used clinical-imaging mismatch criteria 1

2. DEFUSE 3 trial:

   • Included patients between 6-16 hours from last known normal
   • Showed 44.6% functional independence in treatment group vs 16.7% in control
   • Used perfusion-core mismatch criteria 1

Important Considerations and Pitfalls

• Strict adherence to trial criteria is essential: Only use DAWN or DEFUSE 3 eligibility criteria when selecting patients beyond 6 hours 1
• Do not delay treatment: The technical goal should be reperfusion to mTICI grade 2b/3 as early as possible 1
• Collateral flow assessment: May be reasonable to incorporate into decision-making for some candidates 1
• No treatment beyond 24 hours: Current guidelines do not support mechanical thrombectomy beyond 24 hours as there are no randomized trials showing benefit in this time window 1

Procedural Considerations

• Eligible patients should receive IV thrombolysis even if mechanical thrombectomy is being considered 1
• Do NOT wait to evaluate responses to IV thrombolysis before proceeding with catheter angiography for mechanical thrombectomy 1
• The technical goal should be reperfusion to a modified TICI grade 2b/3 1

The paradigm has shifted from a strict "time window" to a "tissue window" approach, but current evidence and guidelines limit mechanical thrombectomy to within 24 hours of symptom onset in carefully selected patients with salvageable brain tissue.