Pediatric Track Session
SCMR 22nd Annual Scientific Sessions
Patients with an atriopulmonary (AP) Fontan have increasing mortality and morbidity as they age. Dilation of the Fontan atrial baffle is associated with increased arrhythmia burden and may also result in energy loss in the Fontan circulation. We hypothesized that increased Fontan atrial baffle volume change or “Fontan baffle stroke volume” during the cardiac cycle is associated with worse exercise capacity and adverse outcomes after the Fontan operation.
This was a retrospective study at Boston Children’s Hospital and Erasmus MC University Medical Center. Patients were included if they 1) have Fontan physiology, 2) had a CMR study and maximal cardiopulmonary exercise test (CPET) within one year of each other, and 3) had CMR image quality adequate for Fontan baffle measurements. Fontan baffle volumes were contoured throughout the entire cardiac cycle just superior to the hepatic veins and inferior to the branch pulmonary arteries on a SSFP axial or extended ventricular short-axis stack. The maximum and minimum volume phases were determined and the Fontan baffle stroke volume was defined as the difference between maximum and minimum volumes. Fontan baffle volumes were indexed to body surface area. Fontan baffle stroke volume was compared between three Fontan types (AP, lateral tunnel [LT] and extracardiac conduit [EC]). Linear regression was used to determine univariate and multivariable predictors of maximal oxygen consumption. To study the differential effect of the Fontan type, an interaction term of Fontan type x Fontan baffle stroke volume was added to the multivariable model.
The study group consisted of 115 patients (median age 19 years, interquartile range 13-29 years). The maximum and minimum baffle volumes and Fontan baffle stroke volume were higher in the AP Fontan compared to the LT and EC Fontan (Table 1). Since the Fontan baffle stroke volume was minimal in patients with an EC Fontan, those patients were excluded from further analysis.
Univariate predictors of a lower maximal oxygen consumption were older age at CMR, AP Fontan, presence of heart failure symptoms, history of stroke or seizures, higher Fontan baffle stroke volume, ventricular mass-to-volume ratio, and higher ventricular end-diastolic volume (Table 2). On multivariable analysis, higher Fontan baffle stroke volume (only in AP Fontans) (P=0.02), history of stroke, and older age at CMR were associated with decreased maximal oxygen consumption (R2 = 0.36). After adjusting for other variables, a baffle stroke volume of 2 ml/m2 predicts maximum oxygen consumption of 29 ml/kg/min, as opposed to 14 ml/kg/min if the stroke volume is 36 ml/m2.
In patients after an AP Fontan, increased Fontan baffle stroke volume was independently associated with lower exercise maximal oxygen consumption. Fontan baffle stroke volume may be a surrogate for energy loss in the Fontan circulation and this may explain its association with lower exercise capacity.