What is endovascular thrombectomy (EVT) for stroke?

What is Endovascular Thrombectomy (EVT) for Stroke

Endovascular thrombectomy (EVT) is a minimally invasive catheter-based procedure that mechanically removes blood clots from large blocked arteries in the brain during acute ischemic stroke, and it dramatically improves clinical outcomes compared to medical therapy alone. 1

How EVT Works

EVT involves threading a catheter through the arterial system (typically via femoral artery access) to the site of the clot in the brain. Once positioned, specialized devices—most commonly stent retrievers or aspiration catheters—physically extract the thrombus to restore blood flow. The goal is achieving complete or near-complete reperfusion (TICI 2b-3 grade) as rapidly as possible. 2

Who Benefits from EVT

Anterior Circulation Strokes (Front of Brain)

For patients with blockages in the internal carotid artery (ICA) or proximal middle cerebral artery (M1), EVT is indicated when ALL of the following criteria are met: 2

• Pre-stroke independence (mRS 0-1)
• NIHSS ≥6 (moderate to severe symptoms)
• ASPECTS ≥6 (limited early infarct on CT)
• Age ≥18 years
• Treatment initiated within 6 hours of symptom onset

For the 6-24 hour window, EVT is indicated when advanced imaging (CTP or MRI) demonstrates salvageable brain tissue using either DAWN or DEFUSE 3 criteria—these trials showed 33% and 28% absolute increases in good outcomes, respectively. 3

Posterior Circulation Strokes (Basilar Artery)

For basilar artery occlusion (BAO), EVT is now strongly indicated based on 2024 guidelines: 1

• Within 12 hours: Class I recommendation (strongest evidence)

  • NIHSS ≥6
  • PC-ASPECTS ≥6
  • Age 18-89 years

• 12-24 hours: Class IIa recommendation (reasonable to perform)

  • Same criteria as above

• Beyond 24 hours: Class IIb (may consider case-by-case)

This represents a major shift—the ATTENTION and BAOCHE trials demonstrated EVT superiority over medical therapy for BAO, ending years of clinical equipoise. 1

Large Core Infarctions

Recent evidence shows EVT benefits patients with larger baseline infarcts than previously thought, though specific ASPECTS thresholds remain debated. 4 Patients with very low ASPECTS require individualized assessment balancing potential benefit against hemorrhage risk.

Critical Timing Principle

Time is brain. Every 15-minute delay to reperfusion reduces the likelihood of good outcome. The procedure should begin (groin puncture) as soon as possible, with target door-to-puncture times under 90 minutes at comprehensive stroke centers. 2

Relationship with IV Thrombolysis

Patients eligible for IV alteplase (tPA) should receive it immediately, even if EVT is planned—do not delay tPA to "wait" for EVT. 5, 6 The IV medication can be administered while simultaneously preparing the angiography suite. Recent evidence suggests combined IV+EVT may produce better reperfusion rates than EVT alone, though this remains an area of active investigation. 6

Procedural Considerations

• Anesthesia: Procedural sedation is generally preferred over general anesthesia unless medically necessary (airway compromise, severe agitation). General anesthesia can cause delays and hypotension. 5

• Device selection: Stent retrievers are the most validated devices, though direct aspiration techniques (ADAPT) are also effective. 6

• Tandem lesions: Patients with concurrent cervical carotid occlusion/stenosis can still undergo EVT, though management of the neck lesion (immediate stenting vs. delayed) requires careful consideration of bleeding risk with antiplatelet agents. 2

Outcomes and Expectations

When performed within appropriate time windows with proper patient selection, EVT provides approximately 20% absolute increase in functional independence (mRS 0-2) compared to medical therapy alone. 7 However, even with successful recanalization, more than 50% of patients do not achieve excellent outcomes, emphasizing the importance of rapid treatment and realistic prognostic discussions. 8

Common Pitfalls to Avoid

1. Delaying IV tPA while arranging transfer for EVT—give tPA first at the spoke hospital
2. Excluding patients >6 hours without advanced imaging—many late-window patients benefit when properly selected
3. Assuming all recanalization equals good outcome—tissue-level reperfusion quality matters, not just vessel opening
4. Overlooking basilar artery occlusion—these patients now have strong evidence for EVT within 24 hours 1

System of Care Requirements

EVT requires coordinated systems including rapid EMS triage, immediate neurovascular imaging capability, 24/7 neurointerventional expertise, and post-procedure neurocritical care in dedicated stroke units. 5 Hub-and-spoke models with clear transfer protocols are essential for maximizing population access.