Original Articles
Effects of Cardiac Rehabilitation and Beta-Blocker Therapy on Heart Rate Variability After First Acute Myocardial Infarction

https://doi.org/10.1016/S0002-9149(98)00021-6Get rights and content

Abstract

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 <0.05]). Rehabilitation modified HRV in groups 1 and 2 (p <0.05), with signs of increased parasympathetic tone (group 1: MSSD +25%, pNN50 +69%, LF/HF −40%; group 2: MSSD +41%, pNN50 +48%, LF/HF −39%). These changes persisted in the long term. In group 3, HRV was unchanged over time. Hence, after AMI, the effects of rehabilitation and β blockers on HRV are not redundant: their association induces a more favorable sympathovagal balance, accelerating the recovery of a normal autonomic profile.

Section snippets

Study Population and Protocol

Fifty-three patients (6 women and 47 men, aged 40 to 66 years) were referred to our center for outpatient cardiac rehabilitation after a first noncomplicated AMI. Most had an inferior AMI (37 of 53, 70%), and most (34 of 53, 64%) had undergone fibrinolysis; in this regard, it is important to notice that HRV retains its prognostic value even when thrombolytic drugs are given.[18]Mean left ventricular ejection fraction was 56 ± 3%. Exclusion criteria were: age >70 years, diabetes, severe

Effect of Therapies on Baseline HRV (Table IB)

When baseline values of HRV indexes were compared 1 month after AMI, patients in group 1 (no β blockade) had signs of a greater sympathetic activation than patients in groups 2 and 3 (i.e., those taking β-blocking therapy).

Effects of Exercise Training on Clinical Variables (Table II)

At the evaluation performed 3 months after AMI at the end of rehabilitation, an increase in exercise duration and final workload was observed in groups 1 and 2, whereas no change was observed in group 3. The rate-pressure product at the same workload was reduced by exercise

Discussion

This study examined the influence of 8 weeks of exercise training with β-blocker therapy on HRV in patients with a recent AMI and preserved systolic function. These interventions seem to share similar effects on prognosis after infarction, reducing mortality from all causes and particularly from sudden death.15, 16, 17Such a favorable outcome could be related to the shift that both therapies induce in cardiovascular autonomic tone toward increased parasympathetic activity.11, 14Our

Acknowledgements

We are grateful to Barbara Avezzù, MS, Maria Teresa Femminis, MS, Alberto Gandolfo, MS, Ada Spiezia, RN, and Paola Zanni, RN, for their valuable and effortless caring of patients undergoing rehabilitation at our institution.

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