AbstractBackgroundNonchicken wing left atrial appendage (LAA) morphology is associated with higher risk for stroke in patients with atrial fibrillation (AF) than chicken wing (CW) morphology.ObjectiveAssess whether LAA morphology predicts the formation of LAA thrombus independent of age, sex, presenting rhythm, left ventricular ejection fraction (LVEF), or anticoagulant use.MethodsA cross‐sectional analysis was performed on patients prospectively enrolled in the Vanderbilt LAA Registry or presenting for transesophageal echocardiogram (TEE) between January 1, 2015, and November 1, 2017 (n = 306). Two physicians independently reviewed TEEs interpreted as having LAA thrombus. Determination of LAA morphology, ejection velocity, and presence of thrombus (n = 102) were based on 0°, 45°, 90°, and 135° TEE views. The control cohort (n = 204) included consecutive AF patients undergoing TEE without LAA thrombus.ResultsLAA morphology in patients with LAA thrombus was: 35% windsock, 47% broccoli, and 12% CW. Windsock (odds ratio [OR], 4.0; 95% confidence interval [CI]: 1.7–9.3, p = .001) and broccoli (OR, 6.6; 95% CI: 2.6–16.6; p < .001) morphology were higher risk for thrombus compared to CW. Female sex predicted higher‐odds for LAA thrombus (OR, 2.6; 95% CI: 1.4–4.8; p = .002) as did LAA‐EV < 20 cm/s (OR, 11.12; 95% CI: 5.6–22.1). Anticoagulation use (OR, 0.5; 95% CI: 0.3–0.9; p = .03) and higher LVEF (OR, 0.95; 95% CI: 0.93–0.98; p < .001) were associated with lower risk. In patients with a CW morphology who had LAA thrombus, 4 of the 7 had an LAA‐EV < 20 cm/s and acute systolic heart failure with LVEF < 30% or active malignancy. In multivariable linear regression analysis controlling for presenting rhythm, anticoagulant use, age, sex, and LVEF, CW morphology appears relatively protective from LAA thrombus (p = .001).ConclusionCW LAA morphology appears relatively protective against the formation of LAA thrombus.