Abdominal Skeletal Muscle Index as a Potential Novel Biomarker in Adult Fontan Patients

BACKGROUND: Fontan palliation results in a chronic multisystem disorder with diminished exercise capacity and increased risk of muscle wasting. The aims of this study were to assess the feasibility of skeletal muscle mass measurements in Fontan patients undergoing magnetic resonance imaging liver surveillance to compare muscle mass with a historic control and to assess its correlation with cardiorespiratory fitness. METHODS: Skeletal muscle area (SMA) and skeletal muscle index (SMI) were measured at T12 and L3. A young, healthy historic cohort was used as a comparison group. RESULTS: Forty patients with a Fontan circulation (mean age, 25.5 ± 7.9 years; 50% were men) were included. Measurements of SMA and SMI were feasible and highly reproducible. Mean SMA and SMI were significantly lower in women compared with men at both T12 (SMA: 25.1 ± 4.9 cm(2) vs 33.5 ± 8.4 cm(2), P < 0.001; SMI: 9.7 ± 2.1 cm(2)/m(2) vs 11.3 ± 2.7 cm(2)/m(2), P = 0.045) and L3 (SMA: 121 ± 12 cm(2) vs 162 ± 24 cm(2), P < 0.001; SMI: 46.9 ± 7.0 cm(2)/m(2) vs 54.5 ± 7.4 cm(2)/m(2), P = 0.002). Mean SMI at L3 was significantly lower in the male Fontan population compared with the healthy historic cohort (54.5 ± 7.4 cm(2)/m(2) vs 60.9 ± 7.8 cm(2)/m(2), P < 0.001), but was similar for women (46.9 ± 7.0 cm(2)/m(2) vs 47.5 ± 6.6 cm(2)/m(2), P = 0.692). SMI at L3, but not at T12, was positively correlated with peak oxygen consumption, oxygen pulse, and workload. Four patients (10%) met criteria for muscle wasting in the sarcopenic range based on L3 measurements. CONCLUSIONS: Abdominal skeletal muscle mass can be reproducibly determined on surveillance liver magnetic resonance imaging scans. Muscle wasting appears to occur commonly in Fontan patients. Further research is needed to better define the value of SMI as a biomarker in the Fontan population.