OVERVIEW OF RR VARIABILITY by J. Thomas Bigger, Jr., M.D.
RR variability has been used for many years as a laboratory tool to evaluate the autonomic nervous system in short term experiments. Since the publication of Kleiger's paper in 1987, interest in the cardiovascular uses of RR variability has grown steadily. RR variability has been used to study cardiovascular physiology and pharmacology, and to predict risk of death in patients with cardiac disease. Spectral analysis is being used more and more commonly due to the realization that this method provides mutually exclusive and all-inclusive measures of RR variability. The first inkling that RR variability had prognostic significance was the 1978 paper of Wolf et al. (1) that reported that the variance of 30 consecutive RR intervals from an admission ECG predicted hospital mortality. Since that time, both time and frequency domain measures of RR variability have been established as excellent predictors of death and non-fatal arrhythmic events after myocardial infarction. For prediction of death, corresponding time and frequency domain measures of RR variability are equivalent. Frequency domain measures of RR variability are more commonly used for mechanistic studies because they resolve parasympathetic/sympathetic influences on the heart better than time domain measures.
The CHRONOS algorithms for computation of RR variability were developed at Columbia University under the direction of Dr. J. Thomas Bigger, Jr. in collaboration with Dr. Jeffrey N. Rottman while he was at Children's Hospital in Boston, MA and Washington University in St. Louis, MO. CHRONOS has become a "gold standard" for the computation of RR interval variability for prediction of death and arrhythmic events in coronary heart disease and for physiologic and pharmacologic studies. This paper describes the algorithms used in CHRONOS and some of the studies that established their utility.
