Autonomic modulation and chronotropic activity during aerobic exercise in patients using atenolol

Abstract

Introduction: The negative chronotropic effect of beta-blockers (BB) can modify itself according to its pharmacokinetics. Objective: To investigate the influence of pharmacokinetics of beta-blockers in heart rate (HR) and autonomic activity (AA) in response to the exercise. Methods: Three groups of hypertensive patients, users of atenolol (n=9), enalapril, (n=8), and a normotensive control group (n=8), performed two sessions of moderate exercise on a cycloergometer, during 40 minutes, whereby 2 hours (Session I), or 23 hours after drug administration (Session II). Records of electrocardiogram were made before, during and after the exercises. Results: The HR was lower in session I comparing with session II of the atenolol group during the exercise. There were no differences in the components of low and high frequency of AA between these sessions. Conclusions: These results confirm the negative chronotropic effect of BB. However, the absence of changes in AA suggests that other mechanisms may be contributing to this phenomenon.