Predictors of higher peak exercise oxygen uptake in a cohort of adult patients with the Fontan circulation

Abstract Background Cardiopulmonary exercise testing (CPET) is particularly useful in patients with the Fontan circulation to quantify exercise capacity and provide prognostic data. Percent achieved of predicted peak exercise oxygen uptake (%VO2pred) is one of the most important CPET parameters. This variable is significantly reduced in most Fontan patients, but the observed range is wide. Purpose The purpose of this study was to determine predictors of higher %VO2pred in a cohort of adult patients with the Fontan circulation. Material and Methods The medical records of 50 adult Fontan patients who underwent CPET were reviewed, including medical history, transthoracic echocardiography, standard 12-lead and 24-hour Holter ECG, ambulatory blood pressure monitoring (ABPM), and multiple laboratory tests. The data obtained were subjected to statistical analysis. All 50 patients were divided into two groups (both N=25) according to the mean value of %VO2pred (group A with %VO2pred62.3% and group B with %VO2pred≤62.3%; %VO2pred=62.3% was a mean value for all patients, the values were normally distributed). Groups were analysed using Student's t-test, Mann-Whitney U test and chi-squared test (where appropriate). Simple linear regression analyses were used to investigate variables that were correlated with %VO2pred, and significant variables were incorporated into multivariable forward stepwise regression analysis. Results The median age of all patients was 22 years (IQR 20-24). The systemic ventricle was dominant left in 23 patients (46%), dominant right in also 23 patients (46%) and of indeterminate morphology in 4 patients (8%). The most important parameters are shown in Table 1. The percent of female gender (64% vs 36%, p=0.047); resting oxygen saturation (94% vs 92%, p=0.03); chronotropic index (CI) 77.78% vs 60.63%, p=0.007; and oxygen uptake at anaerobic threshold (50% vs 43%, p=0.03) were significantly higher in the group A compared to the group B. The use of beta-blockers (16% vs 60%, p=0.003); median number of ventricular extrasystolic beats (2 vs 35, p=0.03) serum concentration of high-sensitivity troponin T hsTnT (4.7 vs 5.7 pg/ml; p=0.03); and mean heart rate reserve (20 vs 50, p=0.004) were significantly lower in the group A compared to the group B. Higher CI (β=0.31; p=0.009), higher maximal diastolic blood pressure during CPET DBPmax (β=0.4; p=0.001) and lower hsTnT (β=-0.31; p=0.007) were significantly and independently associated with %VO2pred. The results of the regression analyses are shown in Table 2. Conclusions Higher CI and DBPmax and lower hsTnT were identified as independent predictors of %VO2pred in a cohort of adult Fontan patients. The findings confirm the importance of chronotropic competence in the Fontan circulation. Furthermore, hsTnT shows potential as a useful biomarker in this population. Further studies are needed to validate these parameters for clinical assessment and risk stratification in Fontan patients.Table 1 Table 2