Elsevier

Heart Rhythm

Volume 7, Issue 7, July 2010, Pages 929-936
Heart Rhythm

Clinical
General
Relationship between changes in heart rate recovery after cardiac rehabilitation on cardiovascular mortality in patients with myocardial infarction

https://doi.org/10.1016/j.hrthm.2010.03.023Get rights and content

Background

Heart rate recovery (HRR) at predischarge exercise stress test predicts all-cause mortality in patients with myocardial infarction (MI), but the relationship between improvement in HRR with exercise training and clinical outcomes remains unclear.

Objective

The purpose of this study was to evaluate the effect of change in HRR after exercise training on clinical outcomes in MI patients.

Methods

The study included 386 consecutive patients with recent MI who were enrolled into our cardiac rehabilitation program. All patients underwent symptom-limited treadmill testing at baseline and after exercise training, and were prospectively followed-up in the outpatient clinic.

Results

Treadmill testing revealed significant improvement in HRR after 8 weeks of exercise training (17.5 ± 10.0 bpm to 19.0 ± 12.3 bpm, P = .011). After follow-up of 79 ± 41 months, 40 (10.4%) patients died of cardiac events. Multivariate Cox regression analysis revealed that diabetes (hazard ratio [HR] 2.28, 95% confidence interval [CI] 1.01–5.19, P = .049), statin use (HR 0.36, 95% CI 0.16–0.80, P = .012), baseline resting heart rate ≥65 bpm (HR 5.37, 95% CI 1.33–21.61, P = .018), post-training HRR <12 bpm (HR 2.49, 95% CI 1.10–5.63, P = .028), left ventricular ejection fraction ≤30% (HR 4.70, 95% CI 1.34–16.46, P = .016), and exercise capacity ≤4 metabolic equivalents (HR 3.63, 95% CI 1.17–11.28, P = .026) were independent predictors of cardiac death. Patients who failed to improve HRR from <12 bpm to ≥12 bpm after exercise training had significantly higher mortality (HR 6.2, 95% CI 1.3–29.2, P = .022).

Conclusion

Exercise training improved HRR in patients with recent MI, and patients with HRR increased to ≥12 bpm had better cardiac survival.

Introduction

The autonomic nervous system plays an important role in regulating the cardiovascular system. Both high sympathetic and low parasympathetic tones have been shown to be associated with increased cardiovascular mortality.1, 2Heart rate recovery (HRR), defined as the fall in heart rate through the first minute after exercise, is a measure of the capacity of the cardiovascular system to reactivate the parasympathetic nervous system after exercise3, 4 and has been found to be an independent predictor of all-cause mortality in various populations.5, 6, 7 Previous studies have shown that HRR measured at predischarge exercise stress test (EST) predicts mortality among survivors of acute myocardial infarction (MI).8

HRR appears to be modifiable by regular exercise,9, 10, 11 presumably due to the favorable effect of exercise on autonomic regulation.12, 13 However, the relationship between improvement in HRR and clinical outcomes after MI remains unclear. The aim of this study was to evaluate the effect of exercise training on HRR in patients with recent MI and the impact of change in HRR on their clinical outcomes.

Section snippets

Study population

This prospective cohort study consisted of consecutive patients who were enrolled into our cardiac rehabilitation program from 1996 to 2007. All patients had confirmed diagnoses of acute MI based on World Health Organization criteria.14 A total of 446 patients who were able to perform symptom-limited EST on treadmill, completed phase 1 and phase 2 of the program with good attendance over 70%, no pacemaker implantation, and no change in medications between the two ESTs were recruited. Among

Study design

Among the 386 patients recruited, 334 underwent an 8-week exercise training program in phase 2 of our program, which consisted of twice-weekly 45-minute scheduled sessions of supervised exercise at an intensity based on individual assessment. The remaining 52 patients did not receive any exercise training because they were included into the control arm of our prior randomized study conducted between 1997 and 2002.15 Nevertheless, all 386 patients received the same magnitude of education,

Exercise testing

Symptom-limited ESTs were conducted in phase 1 (before exercise training) and at the end of phase 2 (after exercise training) using the modified Bruce protocol. Treadmill was terminated within 10 seconds after peak exercise, and patients were allowed to assume a sitting position immediately. Resting heart rate was defined as heart rate before EST during sitting. Peak heart rate was defined as heart rate achieved at peak exercise. Heart rate increment was defined as heart rate increase from

Statistical analysis

Continuous variables are expressed as mean ± SD, and categorical variables are presented in frequency tables. Statistical comparisons were performed using Student's t-test or Pearson Chi-square test, as appropriate. LVEF ≤30% was chosen as a predictive variable of cardiac death, in line with the Multicenter Automatic Defibrillator Implantation Trial II (MADIT II).23 For all other variables, cutoff points were obtained from receiver operating characteristic curve analyses. Hazard ratio (HR) and

Results

Table 1 lists baseline clinical demographic features of the study population. A total of 334 (86.5%) patients received exercise training. More patients in the exercise training group received antiplatelets or warfarin, statins, and revascularizations before enrollment compared to patients without exercise training. Their changes in EST parameters and LVEF during follow-up are listed in Table 2. Peak heart rate, heart rate increment, and HRR increased significantly after completion of phase 2 in

Discussion

Our results demonstrated exercise training improved HRR, LVEF, and exercise capacity in patients with recent MI. In this study, none of the parameters during baseline phase 1 EST, except resting heart rate, predicted cardiac death during long-term follow-up. In contrast, left ventricular dysfunction with LVEF ≤30%, impaired HRR <12 bpm, and exercise capacity ≤4 METs at phase 2 after training were shown to be independent predictors of cardiac death. Furthermore, persistently impaired HRR <12 bpm

Study limitations

First, our study recruited patients who completed phase 1 and phase 2 of the cardiac rehabilitation program with good attendance and were able to perform symptom-limited EST on treadmill. As a result, high-risk populations of patients who could not complete the program due to repeated hospitalizations or could not perform treadmill tests due to poor cardiovascular function were excluded. Indeed, the cardiac death rate was 21% and sudden cardiac death rate was 12.3% among patients excluded (n =

Conclusion

Our study demonstrated that exercise training improved HRR and that patients with persistently impaired HRR <12 bpm after rehabilitation had higher cardiac mortality during long-term follow-up, suggesting that modulation of cardiovascular autonomic control with exercise training may contribute to the long-term beneficial effects of a cardiac rehabilitation program. Its clinical application as a therapeutic target for exercise prescription and medication titration needs to be further addressed

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