Thrombus Histopathology Predicts Outcomes in Cardioembolic Large-Vessel Occlusion

Introduction/Purpose Cardioembolic large‐vessel occlusion (CE‐LVO) is a major cause of acute ischemic stroke treated with mechanical thrombectomy (MT). Previous studies have shown that cardioembolic thrombi are typically more fibrin‐ and platelet‐rich compared to large‐artery atherosclerosis, and cryptogenic thrombi often resemble cardioembolic clots. However, little is known about outcome differences within CE patients themselves. We aimed to assess whether thrombus subtypes (red, white, mixed) influence first‐pass effect (FPE), recanalization, and functional outcomes in CE‐LVO. Materials/Methods This retrospective, two‐center study included 72 consecutive patients with anterior circulation CE‐LVO who underwent MT with thrombus histopathology available. Only patients with cardioembolic etiology were included, confirmed by atrial fibrillation, valvular disease/prosthesis, or heart failure/left ventricular thrombus. Thrombi were stained with hematoxylin‐eosin, and the proportions of RBCs, platelets, and fibrin were assessed by consensus. Thrombi were classified as red when RBCs predominated (>57.5%), white when platelets/fibrin predominated (<42.5% RBC), and mixed when RBCs ranged between 42.5% and 57.5%. The primary outcome was first‐pass effect (FPE), defined as achieving eTICI ≥2c after the first pass. Secondary outcomes included passes, procedure duration, distal emboli, final eTICI ≥2c/3, discharge modified Rankin Scale (mRS), and 90‐day independence (mRS 0‐2). Group comparisons were performed using appropriate statistical tests, with significance set at p<0.05. Results Seventy‐two patients were analyzed (29 white, 26 red, 17 mixed). Mean age was 65.2±13.5 years (p=0.067). Baseline NIHSS was highest in red thrombi (15.8±4.2) and lowest in mixed (12.1±4.9) (p=0.044). Procedural duration and passes did not differ. Distal emboli were less frequent in the red group (38.5%) than in white (69.0%) and mixed (76.5%) (p=0.019). FPE rates were similar (p=0.789). At discharge, red thrombi showed worse outcomes (median mRS 4.5 [2.5‐5], p=0.017). At 90 days, independence was lower in red (30.8%) versus white (65.5%) and mixed (64.7%) (p=0.047). There were no significant differences across groups regarding occlusion site, CE subtype, hyperdense artery sign, use of IV tPA, number of passes, procedure duration, balloon guide use, first technique, or final eTICI ≥2c/3 (all p>0.05). Key variables and outcomes across thrombus subtypes are summarized in Table 1. Conclusion These findings add nuance to prior studies that mainly compared cardioembolic stroke with other etiologies. Thrombus histopathology may serve as a potential biomarker for predicting MT outcomes in CE‐LVO.