Mechanical thrombectomy indications

Core Indications - The Green Light

• Patient Selection:

  • Good pre-stroke functional status (mRS 0-1).
  • Disabling neurological deficit (NIHSS score ≥ 6).

• Vascular & Parenchymal Imaging:

  • Confirmed large vessel occlusion (LVO) in the anterior circulation (ICA or MCA M1 segment).
  • Small established infarct core, indicating significant salvageable brain tissue (penumbra). A non-contrast CT-based ASPECTS score ≥ 6 is the classic threshold.

• Time Window:

  • Standard window: treatment within 6 hours of symptom onset.

⭐ The DAWN and DEFUSE 3 trials radically extended the window to 24 hours for select patients demonstrating a "clinical-core mismatch" on advanced imaging (e.g., CT perfusion), where a small infarct core contrasts with a severe clinical deficit.

Time Windows & Imaging - Race Against the Clock

• Core Principle: Identify Large Vessel Occlusion (LVO) and salvageable brain tissue (penumbra).

• Initial Imaging: Non-contrast CT (to rule out hemorrhage) followed by CT Angiography (CTA) to identify LVO.

• Early Window (< 6 hours from LKW):

  • Criteria: LVO in anterior circulation (ICA, M1) + NIHSS score ≥ 6 + ASPECTS score ≥ 6.

• Late Window (6-24 hours from LKW):

  • Requires advanced imaging (CT Perfusion or DWI-MRI) to assess for mismatch.
  • Mismatch: Small infarct core, large clinical deficit/penumbra.
  • 📌 Mnemonic: DAWN/DEFUSE the time bomb.

⭐ High-Yield: The DAWN trial selected patients with a severe clinical deficit (NIHSS ≥ 10) but a small infarct core on imaging, demonstrating the principle of "tissue window" over "time window."

Key Trials - DAWN & DEFUSE 3

Expanded the mechanical thrombectomy (MT) window beyond 6 hours by prioritizing brain tissue status over strict time cutoffs. Patient selection relies on identifying a mismatch between the clinical deficit or salvageable tissue and the actual infarct size using advanced imaging.

• DAWN Trial

  • Window: 6-24 hours from last known well (LKW).
  • Concept: Clinical-Core Mismatch.
  • Criteria: High NIHSS score (≥10) despite a small infarct core on imaging. This mismatch implies a large salvageable penumbra.

• DEFUSE 3 Trial

  • Window: 6-16 hours from LKW.
  • Concept: Target Mismatch Profile.
  • Criteria: Favorable perfusion imaging profile: small infarct core (<70 mL) and a penumbra-to-core volume ratio ≥1.8.

⭐ These trials proved that selecting patients based on salvageable brain tissue ("tissue is brain") is superior to rigid time windows ("time is brain") for late-presenting large vessel occlusion strokes.

High-Yield Points - ⚡ Biggest Takeaways

• Indicated for large vessel occlusion (LVO) in the anterior circulation (e.g., MCA, ICA).
• Standard treatment window is within 6 hours of symptom onset.
• The window can be extended up to 24 hours for select patients based on perfusion imaging (DAWN/DEFUSE-3 criteria).
• Requires a significant neurological deficit, typically an NIHSS score ≥ 6.
• Imaging must show a small infarct core (e.g., ASPECTS > 6).