Histopathological clot composition as predictors of first-pass effect and 90-day functional outcome following endovascular thrombectomy for acute ischemic stroke due to large vessel occlusion: A prospective cohort study

Objective: First-pass effect (FPE) is an imperative procedural endpoint in endovascular thrombectomy (EVT). This study assessed the association between histopathological clot composition and FPE in patients with acute ischemic stroke due to large-vessel occlusion (LVO). Methodology: This was an prospective observational study conducted at the Department of Neuro Endovascular Surgery, Punjab Institute of Neurosciences, Pakistan, from December 2025 to June 2026. Consecutive adults undergoing EVT with retrieved thrombus available for histopathological assessment were included. Data were analyzed using SPSS 29.0, and logistic regression was used to evaluate factors associated with FPE. Results: A total of 100 patients were included. The mean age was 55.92±13.34 years, and 68.0% (68) were male. The mean onset-to-groin time was 297±71.03 minutes. FPE was achieved in 41 patients (41%). Successful final reperfusion was achieved in 77.0% (77) patients. A favorable 90-day functional outcome (mRS 0–2) was reported in 42.0% (42) patients. RBC-rich clot was associated with higher odds of achieving FPE after adjustment for confounders (adjusted OR 28.12, 95% CI: 5.571-141.993, p<0.001), while fibrin-rich composition had lower odds of achieving first-pass effect (adjusted OR 0.14, 95% CI: 0.039-0.569, p=0.005). The reported regression model had an AUC of 0.914. Conclusion: RBC-rich thrombi were associated with higher adjusted odds of achieving the first-pass effect reperfusion, whereas fibrin-rich clots were difficult to retrieve. Because histological composition is known only after clot retrieval, these findings are exploratory and should not be interpreted as a direct pre-procedural strategy-selection tool.