Effects of metoprolol on heart rate variability in survivors of acute myocardial infarction

Abstract In survivors of acute myocardial infarction (AMI), reduced 24-hour heart rate (HR) variability is an independent predictor of mortality 1 and sudden cardiac death. 2 The attenuated overall variability is supposed to be due to an autonomic imbalance caused by high sympathetic and concomitant low vagal activity, 3,4 which in experimental studies is associated with lowered threshold for ventricular tachyarrhythmias. 5 Beta blockade in patients surviving AMI has proven to be of beneficial effect particularly in the sudden cardiac death rate. 6 The exact mechanism is not clear. 7 This study investigates the effects of β blockade on 24-hour HR variability in patients who have survived AMI.