Abstract 2209: Impaired Diastolic Filling During Exercise Negatively Impacts Exercise Capacity in Children Who Have Undergone the Fontan Operation

Background: Increased cardiac output during exercise relies on synergy between forward pumping of the heart and a peripheral pump, comprised of skeletal muscle function and arteriolar dilation, which augments venous return. The critical component of this two-pump system is the maintenance of normal filling pressures, by enhancing diastolic filling. We hypothesized that children with normal systemic ventricular function, who have undergone the Fontan operation, have impaired diastolic filling during exercise which may negatively impact exercise capacity. Methods: Stress echocardiography was performed during upright cycle ergometry in a group of Fontan patients with normal systolic function (n=14) and a group of normal controls (n=17). Echo parameters obtained at each stage of exercise included early myocardial velocity at the systemic atrioventricular valve lateral annulus (Em), continuous wave Doppler velocity of ventricular inflow (E), calculation of the E/Em ratio (index of ventricular filling pressures), diastolic filling time (DFT), stroke volume (SV) and cardiac output (Q). Heart rate (HR) and maximal aerobic capacity (MVO2) were recorded. All data were normalized to percentage of MVO2. Results: The mean age was 14 years in both groups (p=0.8). The gender distribution was similar (p=0.1). The mean body mass index was slightly lower in the Fontan group (23 vs 19, p=0.05). All studies were judged to be maximal. Exercise and echo data are provided below: