Prognostic Value of Psoas Muscle Area and Density in Patients Who Undergo Cardiovascular Surgery.

BACKGROUND: Low skeletal muscle density, determined using computed tomography (CT), has yet to be examined in terms of muscle function and prognostic capability in patients who require open cardiovascular surgery. This study was performed to examine whether psoas muscle area and density, determined using CT, are associated with postoperative mortality in patients who undergo cardiovascular surgery.

METHODS: We reviewed the findings in 773 consecutive patients who underwent preoperative CT imaging, including the level of the third lumbar vertebra for clinical purposes. We measured grip strength, gait speed, and 6-minute walking distance to assess muscle function before hospital discharge. Skeletal muscle area was calculated from psoas muscle cross-sectional area (in squared centimeters) on preoperative CT images at the level of the third lumbar vertebra divided by the square of the patient's height in metres to give the skeletal muscle index (SMI). Skeletal muscle density determined by muscle attenuation (MA) was calculated by measuring the average Hounsfield units of the psoas muscle cross-sectional area.

RESULTS: The mean age of the study population was 65.0 ± 13.1 years, and 64.7% of the patients were male. Multivariate logistic regression analysis and multivariate Cox regression analysis showed that low MA, but not SMI, was significantly associated with muscle function, and all-cause mortality (P < 0.05). Kaplan-Meier analysis showed that low MA, but not low SMI, predicted mortality (P = 0.014).

CONCLUSIONS: Low skeletal muscle density, but not skeletal muscle area, predicted poorer muscle function and mortality in patients who undergo cardiac surgery.