What is the recommended time window for mechanical thrombectomy (MT) in patients with acute ischemic stroke?

Mechanical Thrombectomy Time Windows for Acute Ischemic Stroke

Mechanical thrombectomy is recommended within 6 hours of symptom onset for patients with large vessel occlusion in the anterior circulation, and can be extended up to 24 hours in selected patients who meet specific clinical-imaging mismatch criteria from the DAWN or DEFUSE 3 trials. 1, 2

Standard Time Window (0-6 Hours)

For patients presenting within 6 hours of symptom onset:

• Strong recommendation (Level I, Grade A evidence) for mechanical thrombectomy plus best medical management (including IV thrombolysis when indicated) 1
• Patient selection criteria:
  • Age ≥18 years
  • Pre-stroke mRS score of 0-1
  • Causative occlusion of internal carotid artery or MCA (M1)
  • NIHSS score ≥6
  • ASPECTS ≥6 2

Extended Time Window (6-24 Hours)

For patients presenting between 6-24 hours:

• 6-16 hours: Strong recommendation (Level I, Grade A evidence) for mechanical thrombectomy in patients with LVO in the anterior circulation meeting DAWN or DEFUSE 3 criteria 1
• 16-24 hours: Reasonable recommendation (Level IIa, Grade B-R evidence) for mechanical thrombectomy in patients meeting DAWN criteria 1

Patient Selection in Extended Window

Advanced imaging is mandatory for patient selection beyond 6 hours:

DAWN Trial Criteria (6-24 hours):

• Clinical-imaging mismatch using NIHSS score and imaging findings (CTP or DW-MRI)
• Demonstrated 49% functional independence in treatment group vs 13% in control 1, 2

DEFUSE 3 Trial Criteria (6-16 hours):

• Perfusion-core mismatch and maximum core size
• Demonstrated 44.6% functional independence in treatment group vs 16.7% in control 1, 2

Special Considerations

Other Vessel Occlusions (within 6 hours)

• M2/M3 MCA occlusions: May be reasonable in carefully selected patients (Level IIb) 1
• Anterior cerebral, vertebral, basilar, or posterior cerebral arteries: May be reasonable in carefully selected patients (Level IIb) 1

Technical Goals

• Achieve reperfusion to modified TICI grade 2b/3 to maximize probability of good functional outcome (Level I, Grade A) 1, 2
• Treatment should not be delayed, with reperfusion achieved as early as possible 2

Important Caveats

• Strict adherence to DAWN or DEFUSE 3 eligibility criteria is essential when selecting patients beyond 6 hours 1, 2
• No evidence supports mechanical thrombectomy beyond 24 hours 2
• IV thrombolysis should not be withheld if indicated, even if mechanical thrombectomy is planned 2
• The paradigm shift from "time window" to "tissue window" has expanded treatment opportunities, but requires proper imaging selection 3

Clinical Impact

The number needed to treat with endovascular thrombectomy to reduce disability by at least one level on the modified Rankin Scale is approximately 2.6, making this one of the most effective interventions in stroke care 3. The DAWN trial showed a 35.5% increase in functional independence, the largest effect ever described in any acute stroke treatment trial 3.