DETERMINANTS OF HEART-RATE-VARIABILITY

Objectives. This study sought to examine clinical determinants of hear t rate variability and to report normative reference values for eight heart rate variability measures. Background. Although the clinical imp lications of heart rate variability have been described, clinical dete rminants and normative values of heart rate variability measures have not been studied systematically in a large community-based population. Methods. The first 2 h of ambulatory electrocardiographic recordings obtained in Framingham Heart Study subjects attending a routine examin ation were reprocessed for heart rate variability, Recordings with tra nsient or persistent nonsinus rhythm, premature beats >10% of total be ats, <1-h recording time or processed time <50% of recorded time were excluded; subjects receiving antiarrhythmic medications also were excl uded. Among five frequency domain and three time domain measures that were obtained, low frequency power (0.04 to 0.15 Hz), high frequency p ower (0.15 to 0.40 Hz) and the standard deviation of total normal RR i ntervals based on 2-h recordings were selected for the principal analy ses. Variables with potential physiologic effects or possible technica l influences on heart rate variability measures were chosen for multip le linear regression analysis, Normative values, derived from a subset of healthy subjects, were adjusted for age and heart rate. Results. T here were 2,722 eligible subjects with a mean age (+/-SD) of 55 +/- 14 years. Three separate multiple linear regression analyses revealed th at higher heart rate, older age, beta-adrenergic blocking agent use, h istory of myocardial infarction or congestive heart failure, diuretic use, diastolic blood pressure greater than or equal to 90 mm Hg, diabe tes mellitus, consumption of three or more cups of coffee per day and smoking were associated with lower values of one or more heart rate va riability measures, whereas longer processed time, start time in the m orning, frequent su praventricular and ventricular premature beats, fe male gender and systolic blood pressure greater than or equal to 160 m m Hg were associated with higher values. Age and heart rate were the m ajor determinants of all three selected heart rate variability measure s (partial R(2) values 0.125 to 0.389). Normative reference values for all eight heart rate variability measures are presented. Conclusions. Age and heart rate must be taken into account when assessing heart ra te variability.