What are the outcomes for thrombectomy (mechanical removal of a blood clot) in patients with acute ischemic stroke presenting in the late window of 6-24 hours?

Thrombectomy Outcomes in the 6-24 Hour Window

Thrombectomy in the 6-24 hour window produces excellent functional outcomes when patients are selected based on salvageable tissue rather than time alone, with approximately 45-49% achieving functional independence compared to 13-17% with medical therapy alone. 1, 2

Evidence for Late Window Thrombectomy

The paradigm shift from "time window" to "tissue window" has revolutionized stroke treatment beyond 6 hours. Two landmark trials definitively established efficacy:

• DEFUSE-3 demonstrated that thrombectomy at a median of 11 hours resulted in 45% functional independence (mRS 0-2) versus 17% with medical therapy alone (P<0.001), representing a 28% absolute increase 1
• DAWN showed even more dramatic results at a median of 12.5 hours, with 49% achieving functional independence versus 13% with medical therapy—the largest treatment effect ever described in acute stroke trials (35.5% absolute increase) 2

Both trials used perfusion imaging to identify salvageable tissue, proving that carefully selected patients benefit substantially even in extended time windows. 3

Patient Selection Criteria for Late Window

For anterior circulation strokes presenting 6-24 hours after last known well, thrombectomy is indicated when imaging demonstrates salvageable tissue. 4

Specific Selection Parameters:

• Vessel occlusion: Proximal middle cerebral artery (M1) or internal carotid artery 1, 2
• Imaging requirements: CT perfusion or diffusion-weighted MRI with perfusion imaging to demonstrate mismatch 4
• DEFUSE-3 criteria: Initial infarct core <70 mL AND perfusion-to-core mismatch ratio ≥1.8 1
• DAWN criteria: Clinical-imaging mismatch based on age-specific NIHSS and infarct volume thresholds 2
• Minimum viability: ASPECTS ≥6 4

The American Heart Association guidelines specifically recommend CTP or DW-MRI with perfusion to demonstrate salvageable tissue for patients beyond 6 hours. 4

Clinical Outcomes and Safety

Functional Outcomes:

• Disability reduction: Number needed to treat of 2.6 to reduce disability by at least one level on the modified Rankin Scale 3
• Mortality benefit: 14% mortality with thrombectomy versus 26% with medical therapy alone in DEFUSE-3 (P=0.05) 1
• Long-term efficacy: Benefits persist for both disability and mortality outcomes 5

Safety Profile:

• Symptomatic intracranial hemorrhage: 6-7% with thrombectomy versus 3-4% with medical therapy alone—no significant difference 1, 2
• Serious adverse events: Comparable between groups (43% thrombectomy vs 53% medical therapy) 1

Real-World Application Beyond Trial Criteria

Approximately 70% of patients presenting in the 6-24 hour window are ineligible for DAWN/DEFUSE-3 trials, most commonly due to large infarct burden (38%). 6 However, real-world data shows that trial-ineligible patients receiving off-label thrombectomy achieved 30% functional independence, with particularly favorable outcomes in patients <80 years. 6 This suggests the potential benefit extends beyond strict trial criteria when clinical judgment supports intervention.

Technical Goals

The angiographic target should be modified TICI 2b/3 reperfusion to maximize functional outcomes. 4, 7 This represents near-complete or complete reperfusion and correlates directly with clinical benefit.

Posterior Circulation Considerations

For basilar artery occlusion, guidelines are more permissive than anterior circulation:

• 0-12 hours: Thrombectomy indicated (Class I, Level B-R) 8
• 12-24 hours: Thrombectomy reasonable (Class IIa, Level B-R) 8
• Beyond 24 hours: May be reasonable case-by-case (Class IIb, Level C-EO), though outcomes are generally poor and benefit uncertain 8

Critical Pitfalls to Avoid

• Do not delay thrombectomy for unnecessary testing—only blood glucose measurement must precede treatment 4
• Do not wait to assess IV thrombolysis response before proceeding to angiography if thrombectomy is being considered 9
• Do not attempt thrombectomy without perfusion imaging in the 6-24 hour window—tissue selection is mandatory for benefit 4, 1
• Patients with ASPECTS 0 or no perfusion mismatch should not undergo thrombectomy as there is no salvageable tissue and increased hemorrhage risk 4

Cost-Effectiveness

Thrombectomy in appropriately selected late-window patients is cost-effective, representing high-value care given the substantial reduction in long-term disability. 5