Protocol for non-invasive assessment of skeletal muscle structure and function in adolescents with single ventricle heart disease: a cross-sectional, case-control study

Background: Congenital heart disease (CHD) is the most common congenital malformation, and the most severe type, single ventricle (SV) heart disease, requires the Fontan surgical palliation. Fontan palliation minimizes hypoxemia and volume overload by separating systemic and pulmonary circulations, resulting in the absence of a sub-pulmonary pump. Skeletal muscle health may have a greater relative contribution to overall functional capacity of those with SV physiology, via the skeletal muscle (SkM) pump mechanism and oxidative capacity. The purpose of this study is to comprehensively evaluate multiple domains of SkM in this population compared to those with normal cardiac anatomy. Methods: Forty SV patients aged 12-21 years old and 40 matched controls will be recruited. During their single study visit, testing will include an echocardiogram with strain analysis and cardiopulmonary exercise testing by cycle ergometry. SkM domains will be evaluated via ultrasound, advanced near-infrared spectroscopy, and biodex testing. Frailty assessment will also be performed. At the conclusion of the study visit, participants will be equipped with a 7-day device-based physical activity accelerometer. Discussion: This study is the first to completely evaluate the SkM domains in adolescents with Fontan. The study aims to determine the differences in SkM in SV patients vs. matched controls. Additionally, the relationship between SkM and measures of cardiac function, fitness, and frailty will be evaluated. This study will lay the groundwork for integration of these SkM domains into future SV exercise and outcomes trials. Trial registration: This study is not a clinical trial study design and was not registered.