Exercise therapy and autonomic function in heart failure patients: a systematic review and meta-analysis.

A large body of evidence exists indicating that autonomic imbalance is characteristic of heart failure, with several parameters of autonomic function associated with adverse clinical outcomes. The aim of this systematic review and meta-analysis was to investigate the effects of exercise training on parameters of autonomic function in patients with heart failure and where possible quantify the size of the effect. We conducted database searches (PubMed, EMBASE and Cochrane Trials Register to 31 March 2017) for exercise-based rehabilitation trials in heart failure; using search terms, exercise training, autonomic function, heart rate recovery, heart rate variability and muscle sympathetic nerve activity. Pooled data indicated a statistically significant increase in heart rate recovery at 1 min (HRR1) in exercise compared to control groups, mean difference 5.90 bpm (95%CI 5.12, 6.69; p < 0.00001). Pooled data also indicated that exercise training improved the short-term heart rate variability (HRV) parameters of root mean square of successive differences between normal heart beats (RMSSD (ms)) [mean difference 10.44 (95%CI 0.60, 20.28, p = 0.04)] and high-frequency normalised units (HFnu) [mean difference 7.72 (95%CI 3.32, 12.12, p = 0.0006), which are predominantly reflective of parasympathetic activity. Analyses also indicated a statistically significant decrease in muscle sympathetic nerve activity (MSNA) bursts/minute (mean difference - 11.09 (95%CI - 16.18, - 6.00; p < 0.0001) and MSNA bursts/100 heart beats (mean difference - 15.44 (95%CI - 20.95, -9.92; p < 0.00001) in exercise groups compared to controls. With improvements in HRR, HRV and MSNA, exercise training appears to facilitate an improvement in parasympathetic tone and reduction in sympathetic activity.