NPPB and hydrops fetalis: HF: heart failure; pre: pre-intervention; post: post-intervention; RER: respiratory exchange ratio; VO2: oxygen consumption; W: watt; ICD: implantable cardioverter defibrillator; AUC: area under the curve; HRV: heart rate variability; SMW: 6-minute walk test; NT-proBNP: N-terminal pro-B-type natriuretic peptide; KCCQ: Kansas City Cardiomyopathy Questionnaire; hsCRP: high-sensitivity C-reactive protein; LVEF: left ventricle ejection fraction.