Phase angle is associated with exercise capacity, muscle strength and body composition in adult patients after Fontan operation

Background

Phase Angle (PA), derived from resistance and reactance obtained via bioelectrical impedance analysis, serves as a non-invasive biomarker of cellular integrity, muscle quality and nutritional status. In patients with heart failure, PA has prognostic value and is consistently associated with exercise capacity and muscle strength. However, data on the clinical value of PA in adult patients with congenital heart disease, specifically those after Fontan operation, remains under-researched.

Purpose

The aim of the study was to evaluate PA in adult patients after Fontan operation compared with healthy controls and to examine its associations with exercise capacity, muscle strength and body composition.

Methods

This single-centre, prospective study included adult patients after Fontan operation and age- and sex- matched healthy controls. Participants underwent a standardized protocol: peripheral muscle strength assessment (maximal handgrip strength) and bioelectrical impedance analysis (PA and body composition). Patients after Fontan operation additionally underwent cardiopulmonary exercise testing to determine peak oxygen uptake (pVO2). Due to sample size, nonparametric tests (Mann-Whitney test and Spearman’s correlation) were performed. Multivariable linear regression was also performed between PA and pVO2, adjusting for age and sex.

Results

Twenty-six patients after Fontan operation (26.6±5.8 years, 12 (46%) females, body mass index 24.3±4.2 kg/m2, 54% with systemic right ventricle, 73% after extracardiac conduit repair) and 13 healthy controls were included. Participants were well-matched for age (p=0.474), sex (p=1.000) or body mass index (p=0.561). PA was significantly lower in patients after Fontan operation compared with controls (6.1±1.0 vs. 7.0±0.7, p=0.005). In patients after Fontan operation, higher PA was significantly associated with higher hand grip strength (p=0.001), higher fat-free mass percentage (p=0.001), and higher fat-free mass index (p=0.002), and inversely associated with fat mass percentage (p<0.001) (Figure 1). Furthermore, PA correlated significantly with pVO2 (p<0.001) and remained a predictor of pVO2 in multivariable regression analysis adjusted for age and sex (B=4.80, 95% CI 1.37–8.23, p=0.009).

Conclusions

In adult patients after Fontan operation PA is significantly reduced compared to healthy controls. It strongly reflects exercise capacity, muscle strength, and body composition. These findings suggest that PA could be a valuable and easily accessible biomarker for monitoring clinical status in this complex population. Larger studies are warranted to determine its prognostic value.

Figure 1. Correlations between Phase Angle (PA) and clinical parameters in adult patients after Fontan operation. Scatter plots illustrating the relationship between PA and peak oxygen uptake (pVO2), maximal handgrip strength (HGS), fat-free mass index (FFMI), and percentage fat mass (FM).