Association between heart rate variability recorded on postoperative day 1 and length of stay in abdominal aortic surgery patients

Objective: To determine whether heart rate variability (HRV) measured in the surgical intensive care unit (ICU) on the first postoperative day predicts clinical outcome in patients undergoing abdominal aortic surgery. Design: Prospective study. Setting: Eighteen-bed surgical ICU of a 1,442-bed university hospital. Patients: One hundred and six patients admitted to the ICU after abdominal aortic surgery. Measurements and Main Results: Twenty-four-hour Holter recordings were analyzed for standard time and frequency domain indices and one nonlinear index (slope) of HRV. Clinical and demographic data were collected from medical records. Patients were dichotomized into short (≤7 days) and long (>7 days) length of stay (LOS) by median split. Patients with long LOS had increased heart rates and decreased short- and intermediate-term HRV but no difference in overall HRV, which primarily reflects circadian rhythm. Independent predictors of LOS were increased age, insulin-dependent diabetes, and decreased HRV. Conclusions: Increased heart rates and decreased intermediate-term HRV indices measured on postoperative day 1 were independent predictors of complicated recovery. The strongest HRV predictors of outcome were natural logarithm very-low-frequency power measured over 24 hrs and during the daytime. Results support the potential use of HRV for the prediction of postsurgical resource utilization.