Associations of segmental phase angle with physical function and prognostic value in patients undergoing cardiovascular surgery.

BACKGROUND AND AIMS: Although whole-body phase angle (PhA) is a recognized prognostic marker in cardiovascular surgery, the clinical significance of segmental PhA and the impact of fluid overload on its interpretation remain insufficiently elucidated. This study investigated the associations between segmental PhA, physical function, and long-term prognosis in patients undergoing cardiovascular surgery.

METHODS

This retrospective cohort study included consecutive patients who underwent elective cardiovascular surgery between October 2016 and March 2021 at Nagoya Heart Center, Japan. Preoperative whole-body, upper extremity, and lower extremity PhA were measured using bioelectrical impedance analysis. We analyzed correlations between PhA and physical functions. Additionally, the impact of fluid overload was assessed by stratifying patients based on an extracellular-to-total body water ratio (ECW/TBW) cut-off of 0.400. Long-term all-cause mortality was evaluated using multivariate Cox regression analyses adjusting for confounders including age, sex, cardiac and renal function.

RESULTS

A total of 859 patients were included in the present analysis (mean age = 68.4 ± 11.9 years, 67.6% male). Segmental PhA significantly correlated with muscle mass, grip strength, and knee extension strength. However, in patients with fluid overload (ECW/TBW ≥0.400), the associations between PhA and physical function were attenuated, and the correlation with age lost statistical significance. Regarding prognosis, low PhA values across all segments were independent predictors of long-term all-cause mortality, even after adjusting for confounders.

CONCLUSIONS

Segmental PhA is a robust predictor of long-term mortality in cardiovascular surgery patients. However, because fluid overload confounds the relationship between PhA and physical function, clinicians must account for fluid status when interpreting PhA as a marker of muscle quality.