ABSENCE OF LOW-FREQUENCY VARIABILITY OF SYMPATHETIC-NERVE ACTIVITY INSEVERE HEART-FAILURE

Background In normal humans, variability of blood pressure, RR interva l, and sympathetic activity occurs predominantly at a low frequency (L F; 0.04 to 0.14 Hz) and a high frequency (HF; +/-0.25 Hz). In conditio ns that increase sympathetic activation in normal humans, the LF compo nent is increased relative to the HF component. Patients with heart fa ilure have high levels of sympathetic activity. We tested the hypothes is 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 ner ve activity (MSNA) and RR interval in 21 patients with chronic heart f ailure and 12 age-matched control subjects. MSNA was higher in patient s with heart failure (62+/-4 bursts per minute) than in the normal sub jects (39+/-4 bursts per minute; P<.01). LF components of RR interval and MSNA variability were lower in the heart failure patients versus t he control subjects (P<.01). HF variability of RR interval and MSNA wa s preserved, at least in part, in heart failure. There was close coher ence between variability patterns of RR interval and MSNA. Furthermore , in 14 heart failure patients who had no LF variability in MSNA compa red with 7 heart failure patients who did manifest LF variability in M SNA, RR interval was shorter, the variance of RR interval was lower, M SNA was higher, respiratory rate was faster, and left ventricular ejec tion fraction was lower (all P<.05). At a median follow-up of 12 month s, 4 heart failure patients had died, all of whom had had absent LF os cillations in MSNA and RR interval. Conclusions The LF variability of sympathetic nerve activity is absent in patients with severe heart fai lure. This disturbed pattern of variability is closely coherent with t he abnormal variability of RR interval. These disturbances of rhythmic oscillations of autonomic outflow, evident in both RR interval and MS NA, suggest a central autonomic regulatory impairment in heart failure and may have important prognostic implications.