Absence of Low-Frequency Variability of Sympathetic Nerve Activity in Severe Heart Failure

Abstract

Background In normal humans, variability of blood pressure, RR interval, and sympathetic activity occurs predominantly at a low frequency (LF; 0.04 to 0.14 Hz) and a high frequency (HF; ±0.25 Hz). In conditions that increase sympathetic activation in normal humans, the LF component is increased relative to the HF component. Patients with heart failure have high levels of sympathetic activity. We tested the hypothesis that the LF component of sympathetic nerve activity variability is increased in heart failure. Methods and Results. We performed spectral analysis of simultaneous recordings of resting muscle sympathetic nerve activity (MSNA) and RR interval in 21 patients with chronic heart failure and 12 age-matched control subjects. MSNA was higher in patients with heart failure (62±4 bursts per minute) than in the normal subjects (39±4 bursts per minute; P<.01). LF components of RR interval and MSNA variability were lower in the heart failure patients versus the control subjects (P<.01). HF variability of...