Introduction: Clot fragmentation and distal embolization is a feared complication of mechanical thrombectomy treatment for acute ischemic stroke, but the frequency, determinants, and outcomes of distal emboli (DE) with modern endovascular reperfusion techniques is poorly characterized. Gradient refocused echo (GRE) MRI, performed before and after intervention, is a novel technique to directly visualize distal emboli and characterize their causes and consequences.
Methods: We analyzed consecutive acute ischemic stroke thrombectomy patients who had MR imaging pre- and post-intervention. Distal emboli were defined as new post-procedure susceptibility vessel signs on GRE, within arteries distal to the target occlusion or within new territories.
Results: Among 50 consecutive patients, age was 70.4 (±15.8), 44% were female, and NIHSS was 15 (IQR 8-19). Thrombectomy techniques include retrievers alone in 42%, aspiration alone in 8%, both retriever and aspiration in 50%, and other (e.g. angioplasty, wire maceration) in 22%. The rate of substantial reperfusion (mTICI 2b-3) was 84%. New distal emboli downstream in the territory of the target occlusion were noted in 22% of patients (single in 91% and multiple in 9%), while no emboli in a new territory were observed. Predictors of distal emboli were: pretreatment with IV tPA (present in 64% of patients with DE vs 26% without, p=0.03); and ICA target occlusion location (64% vs 28%, p=0.04). Nominal differences in the 3-month rate of severely disabled or dead outcome (mRS 5-6) did not reach statistical significance (44% vs 24%, p=0.40).
Conclusions: In the modern neurothrombectomy era, distal emboli within the territory of the target occlusion occur in more than 1 in 5 patients, but embolization to new territories is very uncommon. Predictors of distal emboli are prior intravenous thrombolytic therapy (increasing clot friability) and ICA occlusion location (requiring manipulation of larger thrombi).