What do the distal stroke thrombectomy trials show regarding the effectiveness of mechanical thrombectomy for acute ischemic strokes?

Distal Stroke Thrombectomy Trials: Effectiveness and Outcomes

Mechanical thrombectomy is highly effective for distal vessel occlusions in acute ischemic stroke, with trials showing improved functional outcomes compared to medical management alone, particularly when using stent retrievers within extended time windows up to 24 hours for carefully selected patients. For patients with distal vessel occlusions, mechanical thrombectomy with stent retrievers may be reasonable when treatment can be initiated within 6 hours of symptom onset, though the evidence is less robust than for proximal occlusions. 1

Evidence for Proximal vs. Distal Vessel Occlusions

Proximal Vessel Occlusions (Strong Evidence)

• Established benefit: Multiple trials demonstrate clear benefit for ICA and M1 MCA occlusions 1
• Time window: Up to 6 hours from symptom onset for all eligible patients 1
• Extended window: 6-24 hours for selected patients meeting DAWN or DEFUSE-3 criteria 1
• Outcomes: Significant improvement in functional independence (mRS 0-2) at 90 days 1

Distal Vessel Occlusions (Emerging Evidence)

• M2/M3 MCA occlusions: May be reasonable for carefully selected patients within 6 hours 1
• Other distal vessels: Limited evidence for anterior cerebral, vertebral, basilar, or posterior cerebral arteries 1
• Recanalization rates: High (88%) for distal anterior cerebral artery occlusions 2
• Clinical outcomes: Variable, with 36.6% achieving good outcomes (mRS 0-2) in distal anterior cerebral artery occlusions 2

Patient Selection Criteria

For optimal patient selection, consider:

1. Time from symptom onset:

   • Within 6 hours: Consider for all eligible patients with LVO 1
   • 6-16 hours: Use DAWN or DEFUSE-3 criteria 1
   • 16-24 hours: Use DAWN criteria only 1

2. Imaging criteria:

   • ASPECTS score ≥6 preferred (though may consider <6) 1
   • For extended window: Clinical-imaging mismatch (DAWN) or perfusion-core mismatch (DEFUSE-3) 3

3. Occlusion location:

   • Strong evidence: ICA and M1 MCA 1
   • Reasonable evidence: M2/M3 MCA, anterior cerebral, vertebral, basilar, posterior cerebral arteries 1

Procedural Considerations

• Device selection: Stent retrievers are preferred over older devices like MERCI 1
• Technique: Combined stent-aspiration technique may provide rapid, effective recanalization 1
• Anesthesia: Consider conscious sedation when appropriate, as general anesthesia may be associated with poorer outcomes 1
• Cervical carotid lesions: Management of underlying stenosis remains unclear; stenting may require antiplatelet therapy with increased hemorrhage risk 1

Outcomes and Complications

Effectiveness

• Proximal vessels: Strong evidence for improved functional outcomes 1
• Distal vessels: Pooled data shows favorable direction but non-significant adjusted common OR (1.28; 95% CI, 0.51–3.21) for M2 occlusions 1
• Extended window: 27.5% absolute difference in functional independence favoring thrombectomy (OR=3.33,95% CI=1.81-6.12) 4

Safety

• Distal vessel complications: Relatively rare - vasospasms (10%), dissection (3.3%) 2
• Infarction risk: Despite successful recanalization, approximately half of patients with distal anterior cerebral artery occlusions still sustain partial infarction 2
• Hemorrhage risk: Symptomatic ICH rates appear comparable between mechanical thrombectomy and best medical treatment for distal occlusions (3.6% vs. 0%) 5

Clinical Implications

1. For proximal occlusions (ICA, M1): Strongly consider mechanical thrombectomy within established time windows
2. For M2/M3 occlusions: Consider mechanical thrombectomy within 6 hours in carefully selected patients
3. For other distal vessels: Individualized decision-making based on clinical presentation and imaging
4. For extended time windows: Strictly adhere to DAWN or DEFUSE-3 criteria

Ongoing Research

Current trials like DISCOUNT are investigating the efficacy of mechanical thrombectomy for distal occlusions within extended time windows, which may further expand treatment options 6.

Pitfalls and Caveats

• Patient selection is critical: Recanalization rates consistently exceed rates of good clinical outcomes, highlighting the importance of appropriate patient selection 1
• Time remains crucial: Despite extended windows, faster treatment correlates with better outcomes 1
• Distal embolization: Can occur in approximately 16% of cases during treatment 1
• Reocclusion risk: Arterial reocclusion occurs in about 18% of patients and is associated with poorer outcomes 1