Left atrial mechanics strongly predict functional capacity assessed by cardiopulmonary exercise testing in subjects without structural heart disease

Abstract

Left atrium function is essential for cardiovascular performance and is evaluable by two-dimensional speckle-tracking echocardiography (2D-STE). Our aim was to determine how echocardiographic parameters interrelate with exercise capacity and ventilatory efficiency in subjects with no structural heart disease. Asymptomatic volunteers, in sinus rhythm and with normal biventricular size and function, were recruited from a community-based population. Individuals with moderate-to-severe valvular disease, pulmonary hypertension, and history of cardiac disease were excluded. We performed a transthoracic echocardiogram and assessed left atrial (LA) and left ventricular (LV) mechanics via 2D-STE. Cardiopulmonary exercise testing by treadmill took place immediately thereafter. Peak oxygen uptake (VO₂) served as measure of functional capacity and ventilation/carbon dioxide output (VE/VCO₂) slope as surrogate of ventilation/perfusion mismatch. 20 subjects were included (age 51 ± 14 years, male gender 65%). Peak VO₂ strongly correlated with age (r = -0.83; P < 0.01), with E/e' ratio (r = -0.72; P < 0.01), and with LA reservoir- and conduit-phase mechanics, particularly with LA conduit strain rate (SR) (r = -0.82; P < 0.01), but showed no correlation with LA volume index or LV mechanics. A similar pattern of associations was identified for VE/VCO₂ slope. In multivariate analysis, LA conduit SR (β = -0.69; P = 0.02) emerged as sole independent correlate of peak VO₂, adjusted for age and for E/e' ratio (adjusted r ² = 0.76; P < 0.01). Conduit and reservoir components of LA mechanics displayed strong associations with peak VO₂ and VE/VCO₂ slope. LA conduit-phase SR seems best suited as echocardiographic marker of functional capacity in subjects with no structural heart disease.

Keywords: Cardiopulmonary exercise testing; Functional capacity; Left atrium; Speckle-tracking echocardiography.