Cardiorespiratory Response to Exercise After Modified Fontan Operation: Determinants of Performance

Objectives. This study sought to measure the cardiorespiratory responses to exercise and to identify the perioperative determinants of exercise performance in children, adolescents and young adults who underwent the modified Fontan operation. Background. Several studies of the cardiorespiratory responses to exercise after the Fontan operation have demonstrated subnormal maximal oxygen uptake and exercise heart rate, but the perioperative variables that ultimately affect exercise responses have not been assessed systematically. Methods. The study included 59 of the 548 patients who underwent modified Fontan operation between January 1, 1984 and December 31, 1993 at the Mayo Clinic. Spirometry was performed at rest in all patients before exercise testing. The patients then exercised using previously calibrated cycle ergometer and 3-min incremental cycle exercise protocol. Multiple linear regression analysis was used to determine subset of variables associated with oxygen uptake at peak exercise (V̇o2max), blood oxygen saturation (O2sat) and heart rate at peak exercise (HRmax). Results. V̇o2max ranged from 29% to 95% of normal value; O2sat at peak exercise ranged from 77% to 96%; and HRmax ranged from 39.7% to 97.4% of normal value. Multivariate analysis showed that log V̇o2max/kg2/3 was associated with age at exercise, male gender, body surface area, preoperative confluent pulmonary arteries and rest V̇o2max/kg2/3. Preoperative left pulmonary artery stenosis, the presence of classic Glenn anastomosis at exercise and rest O2sat were associated with O2sat at peak exercise. Age, body surface are at exercise, heart rate at rest and diastolic blood pressure were associated with HRmax at exercise. Conclusions. Subnormal V̇o2max and HRmax values were demonstrated at peak exercise. Several perioperative variables were associated with V̇o2max and O2sat at peak exercise. The presence of classic Glenn anastomosis was associated with decreased O2sat at peak exercise, suggesting intrapulmonary shunting with the classic Glenn anastomosis.