Bioimpedance Spectroscopy in Heart Transplantation: Posttransplant Changes in Body Composition and Effects in Outcomes

Background. Bioimpedance spectroscopy yields measurements of fat-free mass, fat mass, phase angle, and other measures. Bioimpedance spectroscopy has been validated as a preoperative assessment tool in cardiac surgical studies, in which low phase angle predicted morbidity and mortality. No studies have evaluated bioimpedance spectroscopy following heart transplantation. Methods. We evaluated body composition, nutrition status (Subjective Global Assessment, body mass index, midarm muscle circumference, and triceps skinfolds), and functional status (handgrip strength and 6-min walk test) in 60 adults. Body composition measurements via a 256-frequency bioimpedance spectroscopy device included fat and fat-free mass as well as phase angle calculated at 50 kHz. Testing was completed at baseline and 1, 3, 6, and 12 mo following heart transplantation. Mortality and hospital readmissions were analyzed. Results. Phase angle and fat mass increased while fat-free mass decreased; grip strength and 6-min walk test improved after transplantation (all P < 0.001). Improvement in phase angle in the first month postoperatively was associated with reduced risk of readmission. Low perioperative and 1-mo phase angles were associated with prolonged posttransplant length of stay (median: 13 versus 10 d, P = 0.03), increased infection-related readmissions (40% versus 5%, P = 0.001), and increased 4-y mortality (30% versus 5%, P = 0.01). Conclusions. Phase angle, grip strength, and 6-min walk test distance improved after heart transplantation. Low phase angle appears to be associated with suboptimal outcomes and may be a feasible and affordable method to predict outcomes. Further research should ascertain whether preoperative phase angle can predict outcomes.