Endovascular Stroke Treatment Only (ESTO) Trial

The specific aims of this study are to: 1. Determine whether the endovascular treatment (mechanical thrombectomy) alone without using intravenous (IV) recombinant tissue plasminogen activator (rt-PA) in acute ischemic stroke patients demonstrates "promise" or a lack thereof ("futility") in deciding what would be the next phase III trial. 2. Determine the proportion of subjects with slight or no disability (a modified Rankin score (mRS) of 0-2) at 3 months after receiving endovascular treatment (mechanical thrombectomy) alone without using IV rt-PA and compare with historical controls who were treated with IV rt-PA to identify (or lack of) futility. 3. Determine the proportion of subjects with improvement in the National Institutes of Health Stroke Scale (NIHSS) score of ≥8 points or achieving a score of 0-1 at 24 hours after the onset of stroke among subjects with acute ischemic stroke after receiving endovascular treatment (mechanical thrombectomy) alone without using IV rt-PA. 4. Determine the proportion of subjects with angiographic recanalization on post procedure angiogram according to modified Thrombolysis in Cerebral Infarction (TICI) perfusion flow categories among subjects with acute ischemic stroke after receiving endovascular treatment (mechanical thrombectomy) alone without using IV rt-PA. 5. Determine the proportion of subjects with treatment-related serious adverse events (SAEs) within 72 hours and development of symptomatic intracranial hemorrhage at 27 ±3hrs post treatment among subjects with acute ischemic stroke after receiving endovascular treatment (mechanical thrombectomy) alone without using IV rt-PA.