Characterizing the influence of Cardiorespiratory Fitness on Left Atrial size and function in the general population

Increased left atrial (LA) size and reduced LA function have been associated with heart failure and atrial fibrillation (AF) in at risk populations. However, atrial remodeling has also been associated with exercise training and the relationship between fitness, LA size and function has not been defined across the fitness spectrum. In a cross-sectional study of 559 ostensibly healthy participants, comprising 304 males (mean age 46 ± 20 years) and 255 females (mean age 47 ± 15 years), we sought to define the relationship between cardiorespiratory fitness (CRF), LA size and function. We also aimed to interrogate sex differences in atrial factors influencing CRF. Echocardiographic measures included biplane measures of LA volumes indexed to body surface area (LAVi) and atrial deformation using 2D speckle tracking. CRF was measured as peak oxygen consumption (VO2peak) during cardiopulmonary exercise testing (CPET). Using multivariable regression, age, sex, weight, and LAVi (P<0.001 for all) predicted VO2peak (P<0.001, R2 = 0.66 for combined model). After accounting for these variables, heart rate reserve added strength to the model (P<0.001, R2=0.74) but LA strain parameters did not predict VO2peak. These findings add important nuance to the perception that LA size is a marker of cardiac pathology. LA size should be considered in the context of fitness, and it is likely that the adverse prognostic associations of increased LA size may be confined to those with LA enlargement and low fitness.