Phase angle measured by bioelectrical impedance analysis as a predictor of Exercise Capacity in Patients Undergoing late-recovery phase Cardiac Rehabilitation.

Aims: Phase angle (PhA) - a parameter of bioelectrical impedance analysis - is known to reflect cellular nutritional status and cell membrane integrity, and is commonly used as an indicator of muscle quality. This study aimed to explore the association between PhA and exercise capacity and to determine the potential of the former as a novel predictor of the latter in patients undergoing late-recovery phase cardiac rehabilitation (CR).

Methods: This retrospective study included 107 patients undergoing CR. PhA was measured via bioelectrical impedance analysis, and peak V̇O₂ was determined via cardiopulmonary exercise testing before and after CR. Furthermore, correlation and multiple regression analyses were conducted to identify the associations between PhA, peak V̇O₂ and other clinical parameters, such as age, sex, grip strength, skeletal muscle index (SMI), Geriatric Nutritional Risk Index (GNRI) and N-terminal pro-B-type natriuretic peptide (NT-proBNP).

Results: PhA markedly increased after CR in men and women (4.69-4.89 and 4.06-4.47, respectively; P < 0.05 for both). Notably, PhA exhibited a strong correlation with pre- and post-peak V̇O₂, with a notably stronger correlation observed after CR (r = 0.603, P < 0.01). Multiple regression analysis revealed that PhA was an independent predictor of peak V̇O₂ even after adjusting for confounding factors, such as age, sex, grip strength, SMI, GNRI and NT-proBNP.

Conclusion: This study is the first to provide evidence of the significant correlation between PhA and exercise capacity in patients undergoing the late-recovery phase of CR. PhA was found to be a reliable predictor of exercise capacity and holds promise as a novel biomarker for optimising CR interventions and potentially improving patient outcomes.