Left atrial enlargement preserves ellipsoid geometry: evidence against volume-driven spherical remodeling

Introduction Left atrial (LA) remodeling has traditionally been assessed by size parameters; however, increasing attention has been given to geometric alterations, particularly sphericity, as potential markers of adverse remodeling and arrhythmic risk. A more spherical LA has been associated with atrial fibrillation (AF) recurrence and disease severity in selected cohorts. Whether progressive LA enlargement inherently induces spherical transformation across a broad spectrum of pathologies remains unclear. Purpose To determine whether increasing LA volume index (LAVI) is accompanied by geometric transition towards sphericity and to identify demographic, clinical and echocardiographic determinants of spherical remodeling in a large heterogeneous population. Methods A total of 1000 echocardiographic examinations were retrospectively analyzed. LA anteroposterior (LAAPd), transverse (LAT) and longitudinal (LAL) diameters, maximal and minimal LA volumes, and LAVI were measured and indexed to body surface area. Three sphericity indices were calculated: LAT/LAL, LAAPd/LAL and volume-to-max LA diameter sphere ratio. Associations between LAVI categories (normal, mild, moderate, severe enlargement) and sphericity indices (SI) were assessed using correlation and multiple regression analyses adjusted for age, sex, underlying diagnosis, left ventricle (LV) size, LV systolic and diastolic function parameters. Results Progressive LA dilatation from mild to severe was associated with proportional enlargement of all principal diameters (p<0.0005 after comparison among LAVI dilatation categories), demonstrating uniform dimensional expansion. Sphericity indices showed no significant increase across LAVI categories, and correlations between LAVI and sphericity were weak (TABLE 1). Even in severe enlargement, ellipsoid geometry was largely preserved (spherical remodeling varying between 3.0 and 6.8% according to SI parameter used). Spherical remodeling was not independently associated with underlying diagnosis or AF history. In multiple regression analysis, LV size emerged as the only modest independent contributor to increased sphericity (R2=0.19, p=0.01), suggesting a potential role of atrioventricular coupling rather than intrinsic atrial volume expansion alone. Conclusions Progressive LA enlargement does not lead to a spherical atrium. Instead, dilatation reflects balanced dimensional expansion with preservation of ellipsoid geometry, while spherical remodeling appears to represent a distinct morphological phenotype, potentially driven by ventricular–atrial coupling and different pathophysiologic mechanisms rather than volume overload per se.