Rescue Endovascular Treatment After Neurological Deterioration in Initially Mild Basilar Artery Occlusion in an Extended Time Window

Inclusion Criteria: 1. Age ≥18 years. 2. Initially mild ischemic stroke, defined as an initial NIHSS score \<6, with no prior endovascular treatment for the index ischemic event. 3. Basilar artery occlusion, or vertebral artery occlusion resulting in complete interruption of antegrade flow into the basilar artery, documented by CTA, MRA, or DSA during the initially mild phase and before qualifying neurological deterioration. 4. Qualifying neurological deterioration occurring between 24 hours and 7 days after initial symptom onset, or after the last known well if symptom onset is unknown. 5. Qualifying neurological deterioration is defined as an NIHSS score ≥10 with either a ≥4-point increase in total NIHSS or a ≥2-point increase in the NIHSS level-of-consciousness score from the initial NIHSS score and must be documented by certified medical personnel at a medical facility, including a referring hospital. 6. Posterior circulation Acute Stroke Prognosis Early CT Score (pc-ASPECTS) ≥6 on noncontrast CT or diffusion-weighted MRI performed after qualifying neurological deterioration. 7. Time from qualifying neurological deterioration to randomization ≤24 hours. 8. Written informed consent obtained from the patient or a legally authorized representative. Exclusion Criteria: 1. Symptom progression due to intracranial hemorrhage, brain edema, or other clear causes (including but not limited to infarct hemorrhagic transformation, new infarction in non-occluded vascular regions, obstructive hydrocephalus, severe infection, high fever, heart or kidney dysfunction, hypovolemia, or severe electrolyte disturbances). 2. prestroke mRS \>2. 3. Factors in the target vessel that are expected to prevent completion of endovascular treatment. 4. Concurrent anterior and posterior circulation strokes. 5. Prior imaging confirmed or investigator-assessed chronic basilar artery occlusion. 6. Presence of untreated intracranial aneurysms, intracranial tumors (except small meningiomas), or intracranial vascular malformations. 7. Intracranial hemorrhage within the past 6 months, including parenchymal brain hemorrhage, intraventricular hemorrhage, or subarachnoid hemorrhage. 8. Gastrointestinal or urinary tract bleeding, acute myocardial infarction, cranial trauma, or major surgery within the past month. 9. Presence of active bleeding, coagulation disorders, or uncorrectable bleeding tendencies. 10. Platelet count \<40×10\^9/L, or INR \>2 during anticoagulation therapy (irreversible). 11. Severe heart, liver, or kidney dysfunction or other severe systemic late-stage diseases. 12. Known allergy to iodine contrast agents or other treatment-related drugs. 13. Medically uncontrolled refractory hypertension (defined as persistent systolic blood pressure \>185 mmHg or diastolic blood pressure \>110 mmHg) (Note: Participants can be included if their blood pressure is controllable with medication and maintained at an acceptable level). 14. Uncontrollable blood glucose \<2.8 mmol/L or \>22.2 mmol/L. 15. Pregnancy or breastfeeding. 16. Life expectancy \<6 months. 17. Participation in other clinical studies that may affect outcome assessment. 18. Investigator's judgment that the patient is unsuitable for participation in this study or may face significant risks (e.g., due to mental illness, cognitive, or emotional disorders preventing understanding and/or compliance with study procedures and/or follow-up).