EFFECT OF BETA-BLOCKADE ON HEART-RATE-VARIABILITY IN PATIENTS WITH CORONARY-ARTERY DISEASE

Objectives. This study assessed the effects of beta-blockade on heart rate variability in patients with coronary artery disease and determin ed whether the effects of metoprolol in a controlled-release formulati on and atenolol differ with regard to electrocardiographic measures of cardiac autonomic control. Background. Low heart rate variability is common in coronary artery disease and is associated with increased mor tality. Beta-adrenergic blocking drugs may increase heart rate variabi lity in healthy subjects, but there is limited knowledge of whether th ey are able to modify heart rate variability in patients with uncompli cated coronary artery disease. Methods. In a randomly allocated, doubl e-blind crossover study with three 2-week treatment periods, 200 mg of controlled release metoprolol once a day, 100 mg of atenolol once a d ay or placebo once a day were administered in 18 male patients with st able coronary artery disease. The 24-h heart rate variability was meas ured in both the time and frequency domains. Results. Beta-blockade in duced a significant increase in heart rate variability, but no signifi cant differences were found between atenolol and metoprolol. The avera ge 24-h high frequency power increased by 64% after atenolol and by 62 % after metoprolol. The root mean square successive difference of norm al RR intervals increased by 70% after atenolol and by 62% after metop rolol, and the standard deviations of RR intervals increased by 20% an d 16%, respectively. Beta-blockade had no significant effects on the a mplitude of the circadian rhythm of heart rate variability, although b oth metoprolol and atenolol blunted the abrupt decrease of high freque ncy power after arousal. Conclusions. Beta blockade by metoprolol and atenolol enhance the heart rate variability in patients with coronary artery disease. This may contribute to the protective effects of beta- blockade in ischemic heart disease.