Which method of left atrium size quantification is the most accurate to recognize thromboembolic risk in patients with non-valvular atrial fibrillation?

Background: Left atrial (LA) size is a predictor of cardiovascular outcomes in patients in sinus rhythm, whereas conflicting results have been found in atrial fibrillation (AF). This study aims to: (1) Evaluate the accuracy of LA size to identify surrogate markers of an increased thromboembolic risk in patients with AF; (2) Assess the best method to evaluate LA size in this setting. Methods: Cross-sectional study enrolling 500 consecutive patients undergoing transthoracic and transesophageal echocardiography evaluation during a non-valvular AF episode. LA size was measured on transthoracic echocardiography using several methods: anteroposterior diameter, area in four-chamber view, and volumes by the ellipsoid, single-and biplane area-length formulas. Surrogate markers of stroke were evaluated by transesophageal echocardiography: LA appendage (LAA) thrombus, LAA low flow velocities, dense spontaneous echocardiographic contrast and LA abnormality. Results: Except for non-indexed anteroposterior diameter, increased LA size quantified by all the other methods showed a moderate to high discriminatory power to identify all the surrogate markers of stroke. A higher accuracy was observed for indexed LA area in four-chamber view (LAA thrombus: AUC = 0.708, CI95% 0.644-0.772, p< 0.001; LAA low flow velocities: AUC = 0.733, CI95% 0.674-0.793, p< 0.001; dense spontaneous echocardiographic contrast: AUC = 0.693, CI95% 0.638-0.748, p< 0.001; LA abnormality: AUC = 0.705, CI95% 0.654-0.755, p< 0.001), indexed single-plane area-length volume (LAA thrombus: AUC = 0.701, CI95% 0.633-0.770, p< 0.001; LAA low flow velocities: AUC = 0.726, CI95% 0.660-0.792, p< 0.001; dense spontaneous echocardiographic contrast: AUC = 0.673, CI95% 0.611-0.736, p< 0.001; LA abnormality: AUC = 0.687, CI95% 0.629-0.744, p< 0.001), and indexed biplane area-length volume (LAA thrombus: AUC = 0.707, CI95% 0.626-0.788, p< 0.001; LAA low flow velocities: AUC = 0.737, CI95% 0.664-0.810, p< 0.001; dense spontaneous echocardiographic contrast: AUC = 0.651, CI95% 0.578-0.724, p< 0.001; LA abnormality: AUC = 0.683, CI95% 0.617-0.749, p< 0.001), without significant difference between them. Indexed LA area in four-chamber view and indexed area-length volumes also were independent predictors of surrogate markers of stroke. Conclusions: Left atrium enlargement is associated with an increased prevalence of surrogate markers of stroke in patients with non-valvular AF. Indexed LA area in four-chamber view and indexed area-length volumes displayed the strongest association.