STEP is a Randomized, Multifactorial, Adaptive Platform trial that seeks to optimize the care of patients with acute ischemic stroke (AIS) due to large or medium vessel occlusions (LVOs and MVOs).STEP is a registry-based trial; it uses data from existing registries to record information for a subset of the trial Case Report Form (CRF). Additional registry data from non-randomized STEP patients may be used for trial screening, planning, and generalizability assessment purposes.

The research is being done to determine if an investigational drug called "TS23" is safe and effective for the treatment of patients with an ischemic stroke that do not meet the criteria for standard treatments to remove the clot. The best dose of TS23 for these patients is unknown. Prior studies have shown that TS23 works without increasing safety concerns.

The purpose of this research study is to see whether ticagrelor and aspirin or rivaroxaban and aspirin compared to clopidogrel and aspirin will have the most success in preventing another stroke, bleed in the brain, or death in participants who have already had a stroke from a narrowed brain artery.

This is an ancillary study on the Phase 3 parent trial (CREST-2) in which patients with asymptomatic high grade carotid artery stenosis have enrolled to receive either a novel intensive medical management plan alone, or in combination with either Carotid Endarterectomy (CEA) or Carotid artery stenting (CAS). Patients enrolled in CREST-H will undergo a baseline MRI and some patients will also undergo a followup MRI at 1 year. The purpose is to determine whether cognition can be improved by revascularization among the subset of CREST-2 patients with hemodynamic impairment and mild cognitive impairment at baseline.