AGE-RELATED-CHANGES OF SINUS NODE FUNCTION AND AUTONOMIC REGULATION IN SUBJECTS WITHOUT SINUS NODE DISEASE - ASSESSMENT BY PHARMACOLOGICAL AUTONOMIC BLOCKADE

To assess the relationship between aging and autonomic regulation of sinus node function, 56 subjects of various ages (range 14-75 years, mean 43+/-19 years) without sinus node disease were studied. Heart rate, corrected sinus node recovery time and sinoatrial conduction time were measured before (basic) and after (intrinsic) pharmacologic autonomic blockade (propranolol+ atropine i.v.). Percent chronotropies of the above parameters were calculated by a modified Jordan's method. Basic heart rate and basic corrected sinus node recovery time did not vary with age (r=-0.15, r=0.08, respectively), while basic sinoatrial conduction time tended to increase with age (r=0.32, p<0.05). Intrinsic heart rate decreased (r=-0.76, p<0.001), and intrinsic corrected sinus node recovery time and intrinsic sinoatrial conduction time both increased with age (r=0.55, p<0.001; r=0.56, p<0.001, respectively). The younger the subject, the more negative the percent chronotropies of the above parameters were, and the percent chronotropies correlated positively with age (r=0.68, p<0.001; r=0.52, p<0.001 and r=0.34, p<0.05, respectively). In conclusion, intrinsic sinus node functions deteriorated with age. Furthermore, parasympathetic tone on the sinus node functions decreased with age, which may compensate for age-related deterioration of intrinsic sinus node function.