BackgroundEarly neurological deterioration (END) may occur in some patients with acute large vessel occlusion (LVO) undergoing endovascular treatment (EVT). Despite several clear causes of END, such as symptomatic intracranial hemorrhage, failure of recanalization, and intraprocedure complications, a particular END, termed unexplained END (END_unexplained), exists. We aimed to investigate the incidence, independent predictors, and clinical impact of END_unexplained after EVT in patients with acute LVO.MethodsSubjects were selected from the ANGEL-ACT registry. END_unexplained was defined as ≥4-point increase in the National Institutes of Health Stroke Scale (NIHSS) score between baseline and 24 hours after EVT, without the causes listed above. Logistic regression analyses were performed to determine the independent predictors of END_unexplained, as well as the association between END_unexplained and 90-day outcomes assessed by modified Rankin Scale (mRS) score.ResultsAmong the 1557 enrolled patients, the incidence of END_unexplained was 4.3% (67/1557). Admission NIHSS ≤8 (OR=6.88, 95% CI 3.86 to 12.26, p<0.001), general anesthesia (OR=3.15, 95% CI 1.81 to 5.48, p<0.001), admission neutrophil to lymphocyte ratio >5 (OR=2.82, 95% CI 1.61 to 4.94, p<0.001), and number of EVT attempts >3 (OR=2.11, 95% CI 1.14 to 3.89, p=0.018) were associated independently with a high risk of END_unexplained. Furthermore, patients with END_unexplained were associated with a shift toward worse 90-day outcomes (mRS 5 vs 3, common OR=5.24, 95% CI 3.22 to 8.52, p<0.001).ConclusionsEND_unexplained associated with poor 90day outcomes occurred in 4.3% of patients with acute LVO undergoing EVT. Several independent predictors of END_unexplained were identified in this study, which should be considered in daily practice to improve acute LVO management.Clinical trial Registrationhttp://wwwclinicaltrialsgovNCT03370939.