Limitations of the use of spectral analysis of heart rate variability for the estimation of cardiac sympathetic activity in heart failure

Spectral analysis of heart rate variability has gained popularity as a simple, non-invasive tool for assessing autonomic function in both normal subjects and in patients in a variety of clinical settings. However, the use of this method as a means of estimating the magnitude of cardiac sympathetic activation in individual patients with heart failure has proved disappointing, with a lack of concordance with more direct measures of sympathetic outflow. This review will describe the rationale involved in using sympathetic indices obtained from spectral analysis of heart rate variability to assess cardiac sympathetic outflow in normal subjects and patients with heart failure. The specific limitations and technological concerns that dictate how it may most effectively be used in this patient population will be discussed.