Autonomous influence on sinus node and AY node function in the elderly without significant heart disease: assessment with electrophysiological and autonomic tests

Eighteen volunteers with a mean age of 63.3 years, who were asymptomatic and without significant heart disease, were investigated with standard electrophysiological tests, performed before and after inhibition of autonomous neural tone with propranolol (0.1 mg . kg-1) and atropine (0.02 mg . kg-1). In addition heart rate responses to maximal exercise, carotid sinus pressure and bolus injection of isoprenaline (0.01 microgram . kg-1) were studied to evaluate the relation between different functional qualities of the cardiac conduction system. Autonomous tone inhibition (ATI) caused significant reductions in the mean PP-interval, sinus code recovery time (SNRT) and corrected sinus node recovery time (CSNRT). Furthermore, the precision of CSNRT determinations increased after ATI. In contrast, the AV-node effective refractory period and conduction time (AH-interval) did not change after ATI. A significant correlation existed between CSNRT and heart rate after ATI, both variables reflecting sinus node automaticity, while no covariation was found between CSNRT and the response to isoprenaline stimulation. AV-node refractoriness and conduction time showed covariation after, but not before, autonomous inhibition. As elderly asymptomatic non-patients were examined the use of the presented group characteristics as reference values for diagnostic investigations is suggested. For example pre-drug CSNRT above 545 ms (mean + 2 SD) or above 505 ms after ATI, indicates impaired sinus node automaticity.