Guideline Recommendations for Acute Ischemic Stroke Management Beyond 6 Hours

1. Eligibility for Late‑Window Mechanical Thrombectomy

• The 2018 AHA/ASA guidelines state that only patients who meet the DAWN or DEFUSE‑3 trial eligibility criteria should be considered for mechanical thrombectomy between 6–24 hours after symptom onset; patients who do not meet these criteria should receive standard medical therapy. 1
• DEFUSE‑3 required a perfusion‑CT mismatch ratio ≥ 1.8; a ratio of 1.3 falls below this threshold and therefore does not qualify for late‑window thrombectomy. (Class I, Level A) 2
• Both DAWN and DEFUSE‑3 required a large‑vessel occlusion (LVO) in the anterior circulation (e.g., ICA or M1 segment) as a prerequisite for thrombectomy. (Class I, Level A) 1
• DAWN eligibility is based on a clinical‑imaging mismatch that incorporates patient age, NIHSS score, and small core volume; substantial mismatch between deficit severity and core size is mandatory. (Class I, Level A) 2

2. Imaging Thresholds that Exclude Thrombectomy

• A mismatch ratio of 1.3 indicates only a modest amount of salvageable penumbra relative to the ischemic core, making the risk‑benefit profile of thrombectomy unfavorable in the late window. (Class I, Level A) 2
• The DEFUSE‑3 trial demonstrated that patients with mismatch ratios < 1.8 did not derive benefit from thrombectomy, confirming the necessity of the ≥1.8 cutoff. (Randomized controlled trial) 2

3. Immediate Clinical Assessment

• Confirm exact symptom onset time and last‑known‑well time to determine eligibility windows. (Guideline recommendation) 1
• Record the National Institutes of Health Stroke Scale (NIHSS) score and pre‑stroke modified Rankin Scale (mRS) to assess baseline severity and functional status. (Guideline recommendation) 3
• Verify the presence and location of an anterior‑circulation LVO (e.g., ICA or M1) using CTA. (Guideline recommendation) 3
• Calculate the ASPECTS score on non‑contrast CT to evaluate early ischemic changes. (Guideline recommendation) 3

4. Standard Medical Management (when thrombectomy is not indicated)

• Intravenous alteplase should be withheld because the patient is beyond the 4.5‑hour therapeutic window. (Guideline recommendation) 3
• Initiate antiplatelet therapy (e.g., aspirin 160–325 mg) promptly; delaying aspirin while awaiting potential intervention is discouraged. (Guideline recommendation) 4
• Maintain systolic blood pressure ≤ 180 mm Hg and diastolic ≤ 105 mm Hg in patients not undergoing reperfusion therapy. (Guideline recommendation) 4

5. Monitoring and Early Complication Surveillance

• Perform serial neurological examinations every 15 minutes for the first 2 hours, then hourly thereafter. (Guideline recommendation) 4
• Provide continuous cardiac monitoring to detect arrhythmias that may affect stroke outcomes. (Guideline recommendation) 5
• Monitor closely for signs of malignant cerebral edema, especially in large MCA territory infarcts; early neurosurgical consultation is advised. (Guideline recommendation) 4
• Obtain a repeat head CT at 24 hours or sooner if clinical deterioration occurs. (Guideline recommendation) 4

6. Critical Pitfalls to Avoid

• Do not extend DAWN or DEFUSE‑3 eligibility criteria beyond the strict imaging and clinical thresholds established by the randomized trials; doing so exposes patients to procedural risks without proven benefit. (Guideline recommendation) 1
• Do not postpone aspirin administration while awaiting possible intervention; early antiplatelet therapy improves outcomes when thrombectomy is not indicated. (Guideline recommendation) 4
• Recognize that malignant MCA syndrome can develop rapidly; decompressive hemicraniectomy performed within 48 hours can reduce mortality by approximately 50 % in younger patients with extensive MCA infarctions. (Guideline recommendation) 4

Evidence‑Based Management of Distal Anterior Cerebral Artery Occlusions in the Late Time Window

Late‑Window Endovascular Therapy Eligibility

• The 2018 American Heart Association/American Stroke Association (AHA/ASA) guidelines limit thrombectomy performed 6–24 h after stroke onset to patients with proximal anterior‑circulation large‑vessel occlusions (internal carotid artery or M1 segment of the middle cerebral artery) who satisfy DAWN or DEFUSE‑3 criteria. 6
• The ESCAPE, EXTEND‑IA, and SWIFT‑PRIME randomized trials demonstrated clinical benefit of thrombectomy only in patients with internal carotid artery or proximal middle cerebral artery occlusions; distal vessels such as the A2 segment of the anterior cerebral artery were not enrolled. 7
• The 2018 AHA/ASA guidelines explicitly state that late‑window thrombectomy should be offered solely to patients who meet the strict DAWN/DEFUSE‑3 trial criteria; extending these criteria to distal occlusions is not recommended. 6

Perfusion Imaging and Patient Selection

• Perfusion‑imaging mismatch thresholds (e.g., ratio ≥ 1.8) were validated exclusively for selecting patients with proximal large‑vessel occlusions; they do not provide a basis for performing thrombectomy in distal A2 occlusions. [7][8]
• No randomized trial has validated mechanical thrombectomy for distal anterior cerebral artery occlusions—even when imaging shows a large perfusion mismatch (e.g., ratio = 8) and a small core infarct—so current evidence does not support such intervention. [7][6]

Intravenous Thrombolysis Eligibility

• Intravenous alteplase is approved only within 4.5 h of symptom onset; treatment at 7 h exceeds the approved therapeutic window according to AHA/ASA recommendations. 6
• The WAKE‑UP trial extended the thrombolysis window using a DWI‑FLAIR mismatch strategy, but this approach applies solely to wake‑up strokes with unknown onset time and is not applicable to patients with a known 7‑hour delay. 6

Risks of Endovascular Therapy in Distal Vessels

• Procedural complications such as vessel perforation or dissection are more likely in distal vessel thrombectomy, and the potential harm may outweigh the uncertain benefit for A2 occlusions, as highlighted in a 2020 Journal of the American College of Cardiology analysis. 9