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, CI(95%) 0.644- 0.772, p<0.001; LAA low flow velocities: AUC = 0.733, CI(95%) 0.674- 0.793, p<0.001; dense spontaneous echocardiographic contrast: AUC = 0.693, CI(95%) 0.638- 0.748, p<0.001; LA abnormality: AUC = 0.705, CI(95%) 0.654-0.755, p<0.001), indexed single-plane area-length volume (LAA thrombus: AUC = 0.701, CI(95%) 0.633-0.770, p<0.001; LAA low flow velocities: AUC = 0.726, CI(95%) 0.660-0.792, p<0.001; dense spontaneous echocardiographic contrast: AUC = 0.673, CI(95%) 0.611-0.736, p<0.001; LA abnormality: AUC = 0.687, CI(95%) 0.629-0.744, p<0.001), and indexed biplane area-length volume (LAA thrombus: AUC = 0.707, CI(95%) 0.626-0.788, p<0.001; LAA low flow velocities: AUC = 0.737, CI(95%) 0.664-0.810, p<0.001; dense spontaneous echocardiographic contrast: AUC = 0.651, CI(95%) 0.578-0.724, p<0.001; LA abnormality: AUC = 0.683, CI(95%) 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.