Heart rate as marker of sympathetic activity

Objective To determine the value of the supine heart rate as a marker of sy mpathetic tone by assessing, in a large group of subjects, the relationship s between this parameter and two other indices of sympathetic activity, pla sma norepinephrine and sympathetic nerve traffic. Patients and methods We studied 243 subjects aged 50.0 +/- 12.1 years (mean +/- SD). Of these, 38 were normotensive healthy controls, 113 subjects had untreated essential hypertension, 27 were obese normotensives and 65 had c ongestive heart failure. In each subject, over a 10 min supine period, we m easured mean arterial pressure (Finapres), heart rate (electrocardiogram), venous plasma norepinephrine thigh-performance liquid chromatography) and e fferent postganglionic muscle sympathetic nerve activity (microneurography at a peroneal nerve). Results In the whole study group, supine heart rate was correlated with bot h plasma norepinephrine (r=0.32, P<0.0001) and muscle sympathetic nerve act ivity (r=0.38, P<0.0001), This was also the case in the normotensive obese subjects and the heart failure subjects considered separately. Heart rate v alues were greater in the obese and the heart failure patients than in cont rols (75.1 +/- 13.0 and 78.2 +/- 13.0 versus 69.2 +/- 11.6 beats/min; P<0.0 5 and P<0.001, respectively), as were plasma norepinephrine (362.7 +/- 202 and 400.3 +/- 217 versus 230.4 +/- 126 pg/ml; P<0.01 and P<0.001, respectiv ely) and muscle sympathetic nerve activity (44.1 +/- 14.7 and 55.3 +/- 14.3 versus 27.8 +/- 11.0 bursts/min; P<0.001 for both). In contrast, in the es sential hypertensive subjects, no significant relationship was found betwee n these three indices of sympathetic activity. Furthermore, in the hyperten sives, the heart rate was not increased, at variance with the sympathetic n erve traffic, which was greater than in controls (36.2 +/- 10.0 versus 27.8 +/- 11.0 bursts/min, P<0.001). Conclusions These data suggest that the supine heart rate can be regarded a s a marker of intersubject differences in sympathetic tone, and that this i s the case both in the general population and in those with cardiovascular diseases. Its value for this purpose is limited, however, and the limitatio ns may be more evident in essential hypertension than in conditions such as obesity and heart failure. J Hypertens 1998, 16:1635-1639 (C) Lippincott W illiams & Wilkins.