Cardiorespiratory Response to Exercise after the Fontan Procedure for Tricuspid Atresia

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Abstract
Noninvasive exercise testing was used to assess gas exchange in 13 patients age 6–25 yr who had undergone Fontan procedures for tricuspid atresia, five of whom had preexisting Glenn shunts. The results were compared to 28 age- and sex-matched controls. Oxygen saturation was measured by ear oximetry at rest and after exercise. Ventilation oxygen consumption (VO2), carbon dioxide production (VCO2), and heart rate were measured during progressive exercise. The ventilatory equivalents for oxygen (VE/VO2) and carbon dioxide (VE/VCO2), mixed expired pCO2 (PECO2) end-tidal pCO2 (PETCO2), and dead space to tidal volume ratio (VD/VT) were determined during steady state exercise on a cycle ergometer. Heart rate was higher for VO2 by 15% (p < 0.02) and ventilation was higher for both VO2 (by 37%, p < 0.001) and VCO2 (by 27%, p < 0.002) in the patients than the controls. Mean VE/VO2 was 35.4 ± 7.8 (SD) compared to 25.8 ± 3.1 (p < 0.001) and mean VE/VCO2 was 41.7 ± 9.0 compared to 31.6 ± 4.3 (p < 0.001). Mean PECO2 was 21.4 ± 4.4 torr with controls at 27.9 ± 3.8 (p < 0.001) and mean PETCO2 was 33.0 ± 5.3 torr compared to 40.0 ± 3.3 (p < 0.001). The patients had a mean oxygen saturation of 92 ± 5% at rest and abnormal saturation after exercise (87 ± 9, p < 0.005). There were no differences in VE/VO2, VE/VCO2, PECO2, PETCO2, % of Hb saturated with oxygen before and after exercise, or VD/VT ratios between the five patients who had also undergone the Glenn operation and those who had not. Two patients who had right atrium to right pulmonary artery anastomoses demonstrated higher (VE/VO2 and VE/VCO2 ratios, lower end-tidal and mixed expired pCO2, and lower % of Hb saturated with oxygen before and after exercise than the patients with right atrium to right ventricle anastomoses. Patients with tricuspid atresia who have undergone the Fontan operation show high heart rate for oxygen consumption, high ventilation for O2 consumption and CO2 production, low expired CO2 concentrations, and oxygen desaturation during exercise. The results indicate elevated physiological dead space and ventilation perfusion mismatch consistent with maldistribution of pulmonary blood flow in patients with Fontan physiology who have had either a right atrium to pulmonary artery or right atrium to right ventricle connection with or without a previous Glenn shunt. Longer follow-up of these patients will be necessary to determine the late clinical implications of these findings.