Effects of cardiac rehabilitation and beta-blocker therapy on heart rate variability after first acute myocardial infarction

After acute myocardial infarction (AMI), rehabilitation with physical training increases parasympathetic tone. It is unknown whether such a favorable effect of exercise on the sympathovagal balance interacts with effects of other widespread therapies, such as β blockers. In 53 patients after a first, uncomplicated AMI, we studied the combined short- and long- term influence on heart rate variability (HRV) of rehabilitation and β blockade. Patients were divided into 3 groups: group 1 (n = 19) underwent rehabilitation with physical training; group 2 (n = 20) was taking β blockers and underwent rehabilitation; group 3 (n = 14) was taking β blockers and did not enter the rehabilitation program for logistic reasons. Patients were similar as to age, site of infarction, ejection fraction, left ventricular diameter, and baseline stress test duration. Measures of HRV (obtained from a 15-minute resting electrocardiogram) were the standard deviation of the mean RR interval (RRSD), the mean squared successive differences (MSSD), the percent of RR intervals differing >50 ms from the preceding one (pNN50), the low-(LF) and high-(HF) frequency components of the autoregressive power spectrum of the RR intervals and their ratio (LF/HF). Four weeks after AMI, there was less sympathetic predominance in groups 2 and 3 (i.e., patients taking β blockers [p