Assessment by autonomic blockade of age-related changes of the sinus node function and autonomic regulation in sick sinus syndrome

Abstract

Age-related changes of the sinus node (SN) function and the autonomic influence on the SN function were evaluated in 65 patients with sick sinus syndrome (range 14 to 84 years). Heart rate (HR), corrected SN recovery time and sinoatrial conduction time were measured before (basic) and after (intrinsic) autonomic blockade (propranolol 0.2 mg/ kg plus atropine 0.04 mg/kg intravenously). Percent of autonomic chronotropies of the SN function were calculated by the following formulas: (1) — (intrinsic HR — basic HR/intrinsic HR) × 100; (2) (intrinsic corrected SN recovery time — basic corrected SN recovery time/intrinsic corrected SN recovery time) × 100; (3) (intrinsic sinoatrial conduction time — basic sinoatrial conduction time/intrinsic sinoatrial conduction time) × 100. Basic HR, basic corrected SN recovery time and baste sinoatrial conduction time did not vary with age. Intrinsic HR decreased with age, but this correlation was weak (r = −0.54, p < 0.001). Intrinsic corrected SN recovery time and intrinsic sinoatrial conduction time tended to increase with age (r = 0.26, p < 0.05; r = 0.29, p < 0.05, respectively). Percent chronotropies of HR, corrected SN recovery time and sinoatrial conduction time were negative values in younger patients and positive values in elderly patients; they correlated positively with age (r = 0.59, p < 0.001; r = 0.60, p < 0.001; r = 0.43, p < 0.001, respectively). Thus, the basic SN function did not change with age, while the intrinsic SN function deteriorated with age. In the SN function, parasympathetic tone was predominant in younger patients and sympathetic tone was predominant in elderly patients with sick sinus syndrome. Age-related enhancement of sympathetic tone may mask the age-related deterioration of the intrinsic SN function.