Abstract MP2: An Older Thrombus Delays Reperfusion in Mechanical Thrombectomy for Ischemic Stroke

Background: Thrombus formation is a dynamic process and the structure of thrombus changes with time. We examined the effect of thrombus age on the quality of reperfusion and prognosis in mechanical thrombectomy for acute ischemic stroke. Methods: We examined 185 patients who underwent mechanical thrombectomy in 3 stroke centers between January 2015 and December 2019, and pathologically evaluated their retrieved thrombi. Thrombi were classified according to histologically accepted definitions as: fresh, with intact granulocytes; and older, with organization or lytic changes characterized by areas of colliquation necrosis and karyorrhexis of granulocytes. The extent of neutrophil extracellular trap formation (NETosis) in thrombi was assessed on the basis of the density of citrullinated histone H3 positive particles. Baseline characteristics, time to successful reperfusion (eTICI 2b or more), thrombus feature, and functional outcome were compared between the patients with fresh and older thrombi. Results: Fresh thrombi were obtained from 43 patients (23%), and older thrombi, from 142 patients (77%). The stroke subtypes and onset-to-puncture time did not significantly differ between the two groups. The erythrocyte content was higher, whereas the density of macrophages and extent of NETosis were lower in the fresh thrombi. Fresh thrombi were associated with shorter time from puncture to recanalization (median, 48 vs. 62 min, P = 0.004; Figure), and fewer passes before reperfusion (median, 1 vs. 2; P < 0.001). In the multivariate analysis, favorable outcome (mRS ≤ 2) was observed more often in patients with fresh thrombi (adjusted OR, 2.76; 95% CI, 1.20-6.32). Conclusions: An older thrombus necessitated longer procedure time and more device passes, which deteriorate the functional outcome of patients with acute ischemic stroke. Thrombus maturation may contribute to resistance to mechanical thrombectomy.