Mechanical Thrombectomy Guidelines for Acute Ischemic Stroke
Primary Recommendation for Standard Time Window (0-6 Hours)
Perform mechanical thrombectomy plus best medical management (including IV thrombolysis when indicated) for patients with acute ischemic stroke caused by large vessel occlusion of the internal carotid artery or proximal MCA (M1 segment) who meet eligibility criteria and can be treated within 6 hours of symptom onset. 1, 2, 3
Core Eligibility Criteria (0-6 Hours)
- Age: 18 years or older 2
- Pre-stroke function: Modified Rankin Scale (mRS) score 0-1 2
- Stroke severity: NIHSS score ≥6 1, 2
- Imaging: ASPECTS ≥6 on non-contrast CT 1, 2
- Vessel occlusion: ICA or MCA M1 segment confirmed on CTA 2
- Time: Groin puncture within 6 hours of symptom onset or last known well 1, 2
Critical Implementation Points
- Do not delay or withhold IV thrombolysis in eligible patients even when mechanical thrombectomy is planned 4, 2
- Do not wait to assess response to IV thrombolysis before proceeding to catheter angiography—this delay is not recommended and worsens outcomes 1, 2
- Transport patients rapidly to the closest certified primary or comprehensive stroke center with immediate access to cerebral angiography and qualified interventionalists 2
Extended Time Window (6-24 Hours)
For patients presenting 6-16 hours from last known normal, perform mechanical thrombectomy if they have anterior circulation large vessel occlusion and meet DAWN or DEFUSE-3 eligibility criteria. 1, 2
For patients presenting 16-24 hours from last known normal, mechanical thrombectomy is reasonable if they meet DAWN eligibility criteria specifically. 1, 2
DAWN and DEFUSE-3 Criteria Must Be Strictly Followed
The American Heart Association emphasizes that only DAWN or DEFUSE-3 eligibility criteria should be used for patient selection beyond 6 hours—these are the only randomized controlled trials demonstrating benefit in this time window. 1
Key Differences Between Trials:
- DAWN: Used clinical-imaging mismatch (combination of NIHSS score with CTP or DW-MRI findings) for selection 6-24 hours from last known normal, showing 49% vs 13% functional independence (33% absolute difference) 1
- DEFUSE-3: Used perfusion-core mismatch and maximum core size for selection 6-16 hours from last seen well, showing 44.6% vs 16.7% functional independence 1
Required Advanced Imaging for Extended Window
- CT perfusion (CTP) or diffusion-weighted MRI (DW-MRI) with or without MRI perfusion is mandatory 2
- Must demonstrate sizable mismatch between ischemic core and either clinical deficits or area of hypoperfusion 2
Technical Goals and Procedural Standards
The technical goal is reperfusion to modified Thrombolysis in Cerebral Infarction (mTICI) grade 2b/3 to maximize probability of good functional outcome. 1, 4, 2
Why mTICI 2b/3 Matters:
- In the HERMES meta-analysis, 71% (402/570) of patients achieved mTICI 2b/3 reperfusion 1
- Earlier trials with less efficient devices showed much lower recanalization rates (IMS III: 41%, MR RESCUE: 25%), which contributed to their failure to demonstrate benefit 1
- Time to reperfusion is critical—reduced time from symptom onset to reperfusion is highly associated with better clinical outcomes 1
Device Selection:
- Stent retrievers are preferred over older devices like MERCI 2
- Second-generation stent retrievers or catheter aspiration devices should be used 3, 5
Special Vessel Territories and Uncertain Indications
M2/M3 Occlusions (Class IIb - May Be Reasonable)
Mechanical thrombectomy may be reasonable for carefully selected patients with M2/M3 MCA segment occlusions within 6 hours, though benefits are uncertain. 1, 4
- The AHA/ASA considers this a Class IIb recommendation (possible benefit despite uncertain evidence) 4
- HERMES meta-analysis showed positive treatment effect but adjusted odds ratio was not statistically significant (1.28; 95% CI: 0.51-3.21) 4
- No specific guideline recommendations exist for M2 occlusions in the 6-24 hour window—DAWN or DEFUSE-3 criteria should be strictly adhered to 4
- Decision should consider clinical condition, imaging findings, and technical feasibility 4
Posterior Circulation and Other Vessels (Class IIb - May Be Reasonable)
Mechanical thrombectomy may be reasonable within 6 hours for causative occlusions of: 1
- Anterior cerebral arteries
- Vertebral arteries
- Basilar artery
- Posterior cerebral arteries
Benefits remain uncertain for these territories, requiring careful patient selection. 1
Tandem Lesions
Mechanical thrombectomy can be considered for patients with occlusion or stenosis of the cervical ICA in addition to intracranial large vessel occlusion. 2
Patients with Uncertain Benefit (Class IIb)
Mechanical thrombectomy may be reasonable within 6 hours for ICA or proximal MCA (M1) occlusions in patients with: 1
- Pre-stroke mRS score >1
- ASPECTS <6
- NIHSS score <6
Additional randomized trial data are needed for these populations. 1
Common Pitfalls and Critical Caveats
Time-Related Errors:
- Fastest possible reperfusion is essential—every minute counts even within the therapeutic window 1
- Do not use "drip and watch" approach with IV thrombolysis before deciding on thrombectomy 1, 2
Patient Selection Errors:
- Do not extrapolate beyond DAWN/DEFUSE-3 criteria in the extended window—strict adherence is necessary until future trials provide additional evidence 1, 4
- Do not exclude patients who are eligible for IV thrombolysis—they should receive both therapies 4, 2
Facility Requirements:
- Treatment requires experienced stroke center with immediate angiography access 2
- Facilities must define credentialing criteria for interventionalists performing endovascular procedures 2
Complication Awareness:
- Overall risk of complications with sequelae is approximately 15% from recent randomized controlled trials 6
- Major complications include symptomatic intracerebral hemorrhage, vessel perforation/dissection, access-site problems, and embolization to new territories 6, 7
- Early detection and appropriate management can minimize impact of complications 6, 7