IntroductionAn adequate recanalization grade is an independent predictor of a good clinical outcome in patients with acute ischemic stroke. It can be obtained with stent retrievers (SR) and contact aspiration (CA). The aim of this ancillary study of the ASTER trial was to investigate the effect of the regular and irregular phenotype of the M1-middle cerebral artery (M1-MCA) segment occlusion on the procedural and clinical outcomes in the ASTER trial population.MethodsThe predetermined occlusion phenotype assessment was performed by the core laboratory of the ASTER trial and patients with M1-MCA occlusion were included in this study. Clinical and procedural outcomes were analyzed according to the technique used and to the occlusion phenotype.Results188 patients were included in the analysis (95 received SR, 93 CA as first-line treatment). The occlusion phenotypes were graded as irregular in 52.7% of cases (n=99, 95% CI 45.5% to 59.8%). In patients with an irregular occlusion phenotype, complete or adequate recanalization at the end of the first-line strategy was more often achieved with SR than CA (TICI 3: SR 44.1% vs CA 22.5%, OR 0.35, 95% CI 0.14 to 0.89, p=0.027), with a shorter procedure time, a lower number of passes (>2 passes: SR 32.2% vs CA 57.5%, OR 3.31, 95% CI 1.36 to 8.03, p=0.009), and higher rates of favorable clinical outcome (SR 55.2% vs CA 31.6%, OR 0.40, 95% CI 0.16 to 0.97, p=0.042).ConclusionIrregular M1-MCA occlusion phenotypes treated with SR as first-line approach were associated with better procedural and clinical outcomes in the ASTER trial population