Clinical Science (1996) 91, 391-398 (Printed in Great Britain) zyxwvutsrq 39 I Reproducibility of heart rate variability measures in patients with chronic heart failure Piotr PONIKOWSKI, Massimo PIEPOLI, Aham A. AMADI, Tuan Peng CHUA, Derek HARRINGTON, Maurizio VOLTERRANI*, Roberto COLOMBOT, Giorgio MAZZUEROI, Amerigo GIORDANO* and Andrew J. S. COATS zyxwvut Department zyxwvuts of Cardiac Medicine, Imperial College, National Heart and Lung Institute, London, U.K., *Divisione di Cardiologia, Centro Medico di Gussago, Gussago, Italy, TServizio di Bioingegneria and SDivisione di Cardiologia, Centro Medico di Veruno. Veruno, Italy (Received 23 ]anuary/24 June 1996; accepted 24 June 1996) 1. In patients with chronic heart failure, heart rate variability is reduced with relative preservation of very-low-frequency power zyxwvuts ( < 0.04 Hz). Heart rate variability has been measured without acceptable information on its stability and the optimal recording periods for enhancing this reproducibility. 2. To this aim and to establish the optimal length of recording for the evaluation of the very-low-frequency power, we analysed 40, 20, 10 and 5min ECG recordings obtained on two separate occasions in 16 patients with chronic heart failure. The repeatability coefficient and the variation coefficient were calcu- lated for the heart rate variability parameters, in the time-domain (mean RR, SDRR and pNNSO), and in the frequency-domain: very low frequency ( < 0.04 Hz), low frequency (0.04-0.15 Hz), high fre- quency (0.1SO.40 Hz), total power ( O S H z ) . 3. Mean RR remained virtually identical over time (variation coefficient 8%). The reproducibility of time-domain (variation coefficient 25139%) and of spectral measures (variation coefficient 45111%) was very low. The stability of the heart rate variabi- lity parameters was only apparently improved after square root and after log transformation. 4. Very-low-frequency values derived from 5 and 10min intervals were significantly lower than those calculated from 40 and 20 min intervals zyxwvu (P < 0.005). Discrete very-low-frequency peaks were detected in 11 out of 16 patients on the first 40, 20 and 10min recording, but only in seven out of 16 when 5min segments were analysed. 5. The reproducibility of both time or frequency- domain measures of heart rate variability in patients with chronic heart failure may vary significantly. Square root or log-transformed parameters may be considered rather than absolute units in studies assessing the influence of management on heart rate variability profile. Recordings of at least 20 min in stable, controlled conditions are to be recommended to optimize signal acquisition in patients with chronic heart failure, if very-low-frequency power in particu- lar is to be studied. INTRODUCTION Chronic heart failure (CHF) is associated with an impaired autonomic control of the cardiovascular system characterized by generalized sympathetic activation, parasympathetic withdrawal and blunted baroreceptor responses [ 1-41. These abnormalities predict a poor prognosis in CHF and may contri- bute to the further progression of disease [5, zy 61. The analysis of heart rate variability (HRV) is a useful and reliable method of investigating autono- mic control of the heart [7, 81. In patients with CHF there is a marked diminution of all markers of HRV with the development of an altered pattern of spectral frequencies [9-111. The two well- characterized rhythms of RR interval variability, i.e. low-frequency (LF, approximately 0.10 Hz) and high-frequency (HF, approximately 0.25 Hz) rhythms, are suppressed and slower oscillations in HRV (below 0.04Hz) have been described and are relatively preserved in CHF [9]. It is still not clear, however, whether these changes reflect sympatho- vagal imbalance or primarily reflect the degree of left ventricular dysfunction. In particular, although this so-called very-low-frequency (VLF) rhythm may carry important clinical information, the regulatory mechanisms responsible for its genesis are poorly understood [9, 11, 121. Since VLF oscillations con- sist of longer cycles ( > 30 s), conventional 3-5 min periods of recording may not be of adequate length to investigate the VLF band in detail. There are, however, no data available regarding the optimal time of the ECG recording necessary for the appro- priate evaluation of VLF rhythms. Relatively few studies have reported HRV measures derived from Key words: autonomic nervous system, chernoreceptors, heart failure, heart rate variability. Abbreviations CHF, chronic heart failure; HF, high frequency, HRV, heart rate variability; LF, low frequency; RC, repeatability coefficient; TP, total power; VC, variation coefficient. Correspondence: Dr M. Piepoli. Cardiac Department, Imperial College School of Medicine, National Heart and Lung Institute, Dovehouse Street, London SW3 6LY, U.K.