Abstract
PURPOSE: Exercise-based cardiac rehabilitation has been shown to reduce mortality in patients with coronary artery disease. Although the exact mechanisms by which exercise reduces mortality are unclear, one hypothesis invokes the effect of exercise on autonomic tone. Heart rate recovery (HRR) immediately after exercise is a marker of vagal tone that findings have shown to be a powerful predictor of all-cause mortality. This study aimed to evaluate the effect of exercise-based cardiac rehabilitation on HRR.
METHODS: A retrospective study was performed. Patients who completed phase 2 cardiac rehabilitation and had entry and exit exercise stress tests (n = 34) were included in the study. A control sample was identified by review of the exercise stress laboratory database (n = 35). Then HRR at baseline and on follow-up were compared.
RESULTS: After completion of phase 2 cardiac rehabilitation, the HRR improved from 18 +/- 7 bpm to 22 +/- 8 bpm (P < .001). Among controls, the HRR on serial testing were 21 +/- 10 bpm and 21 +/- 9 bpm (P = .649). The mean difference in HRR on follow-up testing was different between those enrolled in a cardiac rehabilitation program and those who were not (P = .002).
CONCLUSION: Exercise training in a cardiac rehabilitation program results in HRR improvement. As a simple parameter for assessing autonomic tone, HRR may be used in a cardiac rehabilitation facility to identify patients with higher risk profiles, and can be useful for evaluating patient outcomes.
Despite advances in medical therapies, minimally invasive treatments, and improved surgical techniques, the risk of subsequent cardiovascular events is 20% to 25% in 5 years. 1 Physical exercise is an important component of the standard therapy for patients after a cardiac event. 2 Pooled data from clinical trials demonstrate significant reductions in all-cause and cardiovascular mortality for patients with coronary artery disease who are enrolled in exercise-based cardiac rehabilitation programs. 3-4 However, the mechanisms by which exercise reduces mortality are unclear. One hypothesis invokes the effect of exercise training on autonomic tone. 5 Exercise training has been shown to modify the sympathovagal control of heart rate toward an increase in parasympathetic tone. 6-7 Increased vagal activity, on the other hand, is associated with reduced risk of death from cardiac-related causes. 8-9
It is considered that the rise in heart rate during exercise is related to the combination of parasympathetic withdrawal and sympathetic activation. 10 The fall in heart rate immediately after exercise, however, is thought to result from reactivation of the parasympathetic nervous system. 10 Recently, the failure of heart rate to decrease rapidly during early exercise recovery was demonstrated to be a predictor of all-cause mortality. 11-13 Heart rate recovery (HRR) is an easily measured parameter of vagal tone that could be used in an outpatient cardiac rehabilitation facility as an outcomes tool that could help to identify patients at increased risk for subsequent cardiovascular events. Although exercise training has been shown to improve heart rate variability and baroreflex sensitivity in patients with coronary artery disease, 7 no evaluation of the effect of cardiac rehabilitation on HRR has been demonstrated previously.
The purpose of this study was to evaluate the effect of a 12-week cardiac rehabilitation program on HRR among patients who had experienced a recent cardiac event. The authors hypothesized that completion of a 12-week supervised exercise training program after a cardiac event will result in HRR improvement.