According to the 2023 American Heart Association/American Stroke Association guidelines, does a patient with a left‑hemispheric ischemic stroke, right hemiplegia, symptom onset about seven hours ago, and a CT‑perfusion mismatch ratio of 1.3 meet criteria for mechanical thrombectomy?

Mechanical Thrombectomy Eligibility at 7 Hours with CT-Perfusion Mismatch Ratio 1.3

This patient does NOT meet criteria for mechanical thrombectomy based on the 2018 AHA/ASA guidelines, because a mismatch ratio of 1.3 falls below the required threshold of ≥1.8 specified in DEFUSE-3 criteria, which must be strictly adhered to for patient selection in the 6-16 hour window. 1

Time Window Classification

Your patient presents at 7 hours from symptom onset, placing them in the extended time window (6-16 hours) where mechanical thrombectomy requires strict adherence to either DAWN or DEFUSE-3 eligibility criteria. 1

DEFUSE-3 Imaging Requirements (6-16 Hour Window)

For patients in the 6-16 hour window, the DEFUSE-3 trial established specific perfusion imaging thresholds that demonstrated benefit (mRS 0-2: 44.6% versus 16.7%; RR 2.67; P<0.0001): 1

• Mismatch ratio ≥1.8 (your patient has 1.3 - does not meet criteria) 1
• Mismatch volume ≥15 mL (not provided in your case) 2
• Ischemic core <70 mL (not provided in your case) 1, 2

DAWN Clinical-Imaging Mismatch Criteria (Alternative)

If DEFUSE-3 criteria are not met, DAWN criteria may be applied for the 6-24 hour window, using clinical-imaging mismatch rather than perfusion ratios: 1

• Age <80 years: NIHSS ≥10 AND core <31 mL, OR NIHSS ≥20 AND core <51 mL 2
• Age ≥80 years: NIHSS ≥10 AND core <21 mL 2

You must verify whether your patient meets DAWN criteria by comparing their NIHSS score to their ischemic core volume on CT-perfusion.

Critical Guideline Mandate

The 2018 AHA/ASA guidelines explicitly state that "DAWN or DEFUSE-3 eligibility should be strictly adhered to in clinical practice" for the extended window, and that "only the eligibility criteria from one or the other of these trials should be used for patient selection." 1 This represents a Class I, Level A recommendation—the highest strength of evidence. 1

Common Pitfall to Avoid

Do not proceed with thrombectomy based on a "favorable" mismatch ratio of 1.3 simply because it exceeds 1.0 or 1.2. 2 The DEFUSE-3 trial specifically required ≥1.8, and using lower thresholds constitutes "patient overselection" that lacks evidence of benefit and may expose patients to procedural risk without proven efficacy. 1, 2

Decision Algorithm for Your Patient

1. Confirm the mismatch ratio is truly 1.3 (below the 1.8 threshold) 1
2. Calculate the absolute mismatch volume and ischemic core volume from the CT-perfusion study 1, 2
3. If mismatch volume <15 mL OR core ≥70 mL: Patient does not meet DEFUSE-3 criteria 1, 2
4. Assess DAWN criteria as backup: Document NIHSS score and compare to core volume thresholds above 1, 2
5. If neither DAWN nor DEFUSE-3 criteria are met: Mechanical thrombectomy is not indicated per current guidelines 1

Additional Considerations

• Intravenous alteplase: If the patient is within 4.5 hours of onset and has no contraindications, IV thrombolysis remains appropriate regardless of thrombectomy eligibility. 3 However, at 7 hours your patient is beyond the IV tPA window. 2

• Proximal vessel occlusion confirmation: Ensure CTA documents ICA or M1 MCA occlusion, as these are the target vessels for extended-window thrombectomy. 1 M2 occlusions have only Class IIb (uncertain) evidence in the early window and no guideline support beyond 6 hours. 4

• Time-dependent outcomes: Even when eligibility criteria are met, each 30-minute delay reduces the probability of good functional outcome by 8-14%, so expedite decision-making. 2