Downstream Occlusion During Mechanical Thrombectomy: Clinical Implications and Endovascular Trajectory

Background/Objectives: Downstream occlusion (DOC) is a commonly observed, yet frequently overlooked, angiographic event during mechanical thrombectomy (MT) for acute large vessel occlusion (LVO). This phenomenon has the potential to complicate procedures and influence outcomes. However, its prevalence, predictors, and endovascular trajectories remain poorly understood. Methods: A retrospective analysis of 703 patients who underwent MT for acute intracranial LVO between 2010 and 2021 at a tertiary stroke center was conducted. DOC was angiographically identified as a newly developed occlusion in a downstream artery following recanalization of the primary occlusion. Multivariate logistic regression was employed to analyze the clinical and procedural predictors of DOC. Endovascular and clinical outcomes were compared between patients with and without DOC. The DOC trajectory, including immediate reperfusion status, subsequent recanalization attempts, and final outcomes, was analyzed based on the occlusion location. Results: DOC was identified in 254 patients (36.1%). Atrial fibrillation and proximal occlusion were independently associated with DOC. Despite DOC adversely affecting endovascular procedural details, patients with DOC demonstrated comparable rates of final successful recanalization (92.5% vs. 91.3%; p = 0.577) and 90-day functional independence (40.2% vs. 46.3%; p = 0.114). Notably, about half of the patients exhibited an immediate modified Thrombolysis In Cerebral Infarction (mTICI) grade 2b at the time of DOC. Further recanalization attempts were undertaken in 67.7% of DOC cases, resulting in enhanced mTICI grades in 76.7% of cases and achieving final successful recanalization in 94.2% of cases. The functional advantages of additional recanalization attempts varied depending on DOC location but were generally limited. Conclusions: Despite its procedural complexity, DOC did not significantly compromise final recanalization or functional outcomes. Many cases were effectively managed with additional endovascular treatment, highlighting the importance of achieving sufficient final recanalization.