Abstract
Background Although heart rate variability (HRV) is altered in a variety of pathological conditions, the association of reduced HRV with risk for new cardiac events has not been studied in a large community-based population.
Methods and Results The first 2 hours of ambulatory ECG recordings obtained on subjects of the Framingham Heart Study who were free of clinically apparent coronary heart disease or congestive heart failure were reprocessed to assess HRV. Five frequency-domain measures and three time-domain measures were obtained. The associations between HRV measures and the incidence of new cardiac events (angina pectoris, myocardial infarction, coronary heart disease death, or congestive heart failure) were assessed with proportional hazards regression analyses. There were 2501 eligible subjects with a mean age of 53 years. During a mean follow-up of 3.5 years, cardiac events occurred in 58 subjects. After adjustment for age, sex, cigarette smoking, diabetes, left ventricular hypertrophy, and other relevant risk factors, all HRV measures except the ratio of low-frequency to high-frequency power were significantly associated with risk for a cardiac event (P=.0016 to .0496). A one–standard deviation decrement in the standard deviation of total normal RR intervals (natural log transformed) was associated with a hazard ratio of 1.47 for new cardiac events (95% confidence interval of 1.16 to 1.86).
Conclusions: The estimation of HRV by ambulatory monitoring offers prognostic information beyond that provided by the evaluation of traditional cardiovascular disease risk factors.
Key Words: • heart rate • electrocardiography • prognosis • epidemiology
Introduction
He a rt rate variability, or heart period variability, is a measure of the cyclic variations of beat-to-beat (RR) intervals that reflects cardiac autonomic function. I Heart rate variability is influenced by various physiological and pathological conditions. 2-13 For several decades, obstetricians have recognized diminished beat-to-beat variation in fetal heart rate as an indicator of distress. 14 In cardiology, prior studies have documented adverse prognostic implications of reduced heart rate variability in patients after myocardial infarction 15·17 and with other pathological conditions. 18-2\ Recently, we reported-" an association between reduced heart rate variability and risk for all-cause mortality in elderly original participants in the Framingham Heart Study. The relation of altered heart rate variability to risk for cardiac events has not been studied in the general population.
The present investigation was undertaken to examine the association of reduced heart rate variability with risk for cardiac events in a large population-based sample Subjects in this study included elderly participants in the original Framingham Heart Study and younger participants in the Framingham Offspring Study. The study setting provides an opportunity to explore the prognostic implications of heart rate variability measures in .3. sample in which referral bias is inherently minimal.
Acknowledgments
This study was supported by grants from the Eleanor Naylor Dana Foundation and Cardiodara/Mortara Inc.