Prognostic Value of Submaximal Exercise Data for Cardiac Morbidity in Fontan Patients

Introduction Submaximal exercise parameters are associated with an increased risk of hospitalization in patients with heart failure, but the implication in patients with Fontan circulation remains unknown. We investigated the prognostic value of these parameters in a Fontan cohort, in whom maximal exercise effort is often limited. Methods Fifty-two Fontan patients received cardiopulmonary exercise tests at least 12 months after Fontan completion. We evaluated two maximal parameters (peak oxygen consumption (VO2) and HR reserve) and two submaximal parameters (oxygen uptake efficiency slope (OUES) and minute ventilation (Ve) to carbon dioxide elimination (VCO2) slope). Results The peak VO2 and OUES were 58.0% +/- 11.2% and 56.6% +/- 14.5% of the age- and sex-related predicted values. In the subsequent follow-up (median, 22.7 months), 11 patients (21%, including one death) exhibited cardiac morbidity, defined as cardiac-related hospitalization. Time-dependent receiver operating characteristic curve analysis demonstrated that only submaximal parameters were related to 2-yr cardiac morbidity (area under the curve for OUES 0.781, P = 0.018; for Ve/VCO2 slope 0.714, P = 0.04), even in the subgroup achieved maximal exercise effort. The optimal threshold value for OUES was 45%, and for the Ve/VCO2 slope, it was 37. Furthermore, the OUES conveyed independent prognostic information beyond resting oxygen saturation and a history of heart failure or protein-losing enteropathy. Conclusion Submaximal exercise parameters provide superior prognostic information to maximal exercise data for predicting cardiac morbidity in Fontan patients. Moreover, the association between the OUES and cardiac morbidity is independent of relevant baseline clinical information.