The Influence of Atrial Strain on Functional Capacity in Patients with the Fontan Circulation

Speckle-tracking echocardiography has been used to assess atrial function. This analysis is feasible in univentricular hearts. The aim of this study was to characterize the relationship between atrial strain and functional capacity in the Fontan circulation. Apical four-chamber echocardiographic loops of 39 Fontan patients were reviewed. The dominant atrium was assessed for active (ε_act), conduit (ε_con), and reservoir (ε_res) strain and ε_act/ε_res ratio. Cardiopulmonary exercise test was performed on the same day and oxygen uptake (VO₂) at ventilatory threshold (VT) and peak VO₂ were chosen as the dependent variables. Statistical analysis was performed using SPSS^® version 23. Unpaired t test was used for binomial and continuous variable correlation; single and multivariable linear regression were used for continuous variable correlation. Statistical significance was defined as p value < 0.05. VO₂ at VT as a percentage of predicted VO₂ was 36.8% (SD 10.7). Peak VO₂ was 64.7% (SD 18.9) of the predicted value. In univariate analysis, both were associated with age, atrioventricular regurgitation, ejection fraction, ε_res, ε_con, and ε_act/ε_res. In multivariate regression, higher VO₂ at VT and peak VO₂ were associated with younger age (p = 0.003 and p = 0.001, respectively) and higher ε_con (p = 0.026 and p = 0.020). Evaluation of heart function is difficult in the Fontan circulation, hindered by complex ventricular morphology and lack of normative data. VO₂ provides a good surrogate. Atrial strain parameters are compromised in these patients and associated with VO₂. Therefore, whenever possible, atrial strain should be measured as it may provide a new method of risk stratification.