Variations of normal sinus node function in relation to age: role of autonomic influence

An electrophysiological study of sinus node function, includingmeasurements of resting heart rate, maximal corrected sinusnode recovery time and sinoatrial conduction time, was performedin 30 patients, 12–79 years of age, without any clinical,electro car diographic or electrophy siological evidence ofsinus node disease. To analyse autonomic influences, variables were measured beforeand after sympathetic and parasympathetic blockade. No significantcorrelations were observed between age and electrophysiologicalmeasurements of sinus node function at the control study orafter sympathetic blockade. In contrast, the electrophysiologicalparameters of intrinisic sinus node activity were correlatedwith age and showed a progressive lengthening of mean sinuscycle length, of maximal corrected sinus node recovery timeand of sinoatrial conduction time. In addition, measurements after vagolysis suggest a progressivedecrease of parasympathetic activity with increasing age. These data also indicate that the respective role of the twocomponents of the autonomic nervous system vary with increasingage: parasympathetic activity predominates in younger subjects;sympathetic and parasympathetic tones are equilibrated in oldersubjects. The normal sinus node function represents an equilibrated system:in parallel with ageing of the intrinsic properties of the sinusnode, parasympathetic activity decreases so that basal propertiesremain stable throughout life.