SARCOPENIA IN OLDER ADULTS UNDERGOING CARDIAC SURGERY

Abstract

Sarcopenia, defined as age-related loss of muscle mass and strength, is one of the biological hallmarks of frailty. In practice, muscle mass is typically measured using a dual x-ray absorptiometry (DXA) scan, while strength is measured using physical performance tests. However, DXA may be less accurate in acute cardiac patients due to the confounding effect of body edema, and strength alone may be a superior indicator of muscle quality in aging. A convenience sample of older adults referred for cardiac surgery were prospectively consented and enrolled at the Jewish General Hospital. After a structured questionnaire and physical performance battery, patients underwent a DXA scan (GE Lunar) to measure their appendicular muscle mass (AMM) – the sum of fat-free tissue in their arms and legs. Patients were categorized as sarcopenic based on the European Working Group guidelines if they had low AMM and low strength as measured by the timed chair rise test >15 seconds. Both non-indexed and height-squared-indexed cutoffs were explored for low AMM. A Cox proportional hazards model was used to test the association between sarcopenia (or its individual components) and all-cause mortality adjusting for age, sex, and cardiac surgery type. The cohort consisted of 134 patients with a mean age of 70.7 ± 10.2 years and 23% female. The cardiac surgery type was isolated coronary bypass in 58%, valve surgery in 30%, and decision not to proceed with surgery in 12%. The mean AMM was 24.2 ± 5.1 kg in men and 21.0 ± 5.2 kg in women. The prevalence of sarcopenia was 10% and 13% using non-indexed and indexed cutoffs, respectively, similar in men and women. In the multivariable model, sarcopenia was not associated with mortality (N=24) over 2 years of follow-up, and neither was AMM alone. Timed chair rise time alone was associated with mortality as a continuous variable and a dichotomous >15 second variable (HR 7.72, 95% CI 1.75 to 34.11). Lower-extremity muscle strength is more predictive than muscle mass or DXA-based sarcopenia in predicting survival after cardiac surgery.