Background and Purpose- Efficacy of endovascular thrombectomy has been demonstrated up to 24 hours after stroke onset in patients selected with perfusion imaging. We hypothesized that a persistent favorable perfusion profile exists in some patients beyond 24 hours from the onset and can be predicted by a lower baseline hypoperfusion intensity ratio, which indicates favorable collaterals. Methods- We identified control arm patients from the DEFUSE 3 trial (The Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke) with a diffusion weighted imaging and perfusion magnetic resonance imaging performed 24 hours following randomization and compared imaging and clinical variables between patients with persistent mismatch versus patients who no longer had a mismatch 24 hours after randomization. Results- Eighteen percent of the control arm patients had a persistent favorable profile >38 hours after last known well time. These patients had similar baseline diffusion weighted imaging and Tmax >6 seconds volumes as patients whose initially favorable perfusion profile became unfavorable (diffusion weighted imaging lesion 7 versus 17 mL; P=0.17, Tmax >6 seconds 98 versus 100 mL; P=0.48) yet experienced less infarct growth (15 versus 59 mL; P<0.001) and had 3-fold smaller infarct volumes (15 versus 59 mL; P<0.001) 24 hours after randomization. Patients with a persistent favorable perfusion profile had a significantly lower hypoperfusion intensity ratio on baseline imaging (0.2 versus 0.4; P<0.01). Favorable clinical outcome at 90 days occurred in only 10% of the persistent mismatch patients. Conclusions- About 20% of patients with a middle cerebral artery or internal carotid artery occlusion who present in an extended time window and are not treated with thrombectomy have a persistent mismatch for at least an additional 24 hours. These patients have a favorable hypoperfusion intensity ratio at presentation, may experience delayed infarct expansion, and have poor clinical outcomes. Clinical trials are needed to determine if patients with a favorable perfusion profile benefit from reperfusion beyond 24 hours. Clinical Trial Registration- URL: https://www.clinicaltrials.gov . Unique identifier: NCT02586415.
Keywords: magnetic resonance imaging; reperfusion; stroke; thrombectomy.