Asian Cardiovasc Thorac Ann 2008;16:202-207
© 2008 Asia Publishing EXchange Ltd
Effect of Completion of Cardiac Rehabilitation on Heart Rate Recovery
Abbas Soleimani, MD,
Mojtaba Salarifar, MD,
Seyed E Kasaian, MD,
Saeed Sadeghian, MD,
Mostafa Nejatian, MD,
Ali Abbasi, MD
Tehran Heart Center, Medical Sciences/University of Tehran, Tehran, Iran
For reprint information contact: Abbas Soleimani, MD, Tel: 98 21 8802 9256, Fax: 98 21 8802 9256, Email: soleimania{at}yahoo.com, Tehran Heart Center, North Kargar Street, PO Box 1411713138, Tehran, Iran.
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ABSTRACT
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To evaluate the effects of a cardiac rehabilitation program on heart rate recovery after percutaneous transluminal coronary angioplasty, a historical cohort study was performed on 436 patients of whom 285 were grouped on completion of 5, 10, or 24 training sessions. All 3 groups showed significant improvements in heart rate recovery, peak heart rate during treadmill testing, and end-training heart rate, from baseline to follow-up. Heart rate recovery on follow-up correlated significantly with the number of completed exercise sessions. The number of sessions, baseline ejection fraction, and age were independent predictors of mean post-training heart rate recovery. The cardiac rehabilitation program had a significant effect on peak heart rate and heart rate recovery, regardless of the underlying characteristics of the patients.
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INTRODUCTION
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Cardiac rehabilitation is a well-established treatment for patients with coronary artery disease. Meta-analysis of pooled data from clinical trials and cohort studies demonstrated significant reductions in all-cause and cardiovascular mortality in patients enrolled in exercise-based cardiac rehabilitation programs.1–4 Although the precise mechanism by which exercise reduces the mortality rate is unclear, it has been shown that exercise training modifies the autonomic control of cardiovascular function. An early fall in heart rate (HR) after exercise is thought to result from increased vagal activity. Recently, HR recovery was demonstrated to be a powerful predictor of all-cause mortality.5,6 Cardiac rehabilitation has also been associated with an improvement in HR recovery in patients with heart failure, coronary artery bypass grafts, or prior myocardial infarction.7–13 However, no cohort evaluation of the effects of cardiac rehabilitation in patients with percutaneous transluminal coronary angioplasty (PTCA) has been carried out. The purpose of this study was to evaluate the effects of an exercise-based cardiac rehabilitation program on HR recovery after PTCA to clarify whether exercise training could result in better HR recovery.
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PATIENTS AND METHODS
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Our study population was drawn from a large cohort of 436 patients (mean age, 55.96 ± 11.10 years; males, 71.8%) who had undergone PTCA at Tehran Heart Center between July 2004 and January 2006 and were enrolled in an exercise-based cardiac rehabilitation program (phase II). The charts of all patients who attended a session of cardiac rehabilitation were reviewed. The investigation was approved by the institutional review board governing the participation of human subjects in research at the Tehran University of Medical Sciences. It also conformed with the principles outlined in the Declaration of Helsinki. The inclusion criteria were: no previous coronary artery bypass surgery; no neurologic impairment (stroke, peripheral neuropathy, or traumatic brain injury); no severe musculoskeletal disease (fracture, amputation); and no complications during hospitalization, such as severe infection, shock, arrhythmia, or prolonged ventilator dependence. Patients were excluded if they displayed uncontrolled dysrhythmia during exercise training, such as atrial flutter, fibrillation, or continuous ventricular tachycardia, or if ischemic changes were observed on an electrocardiogram during treadmill exercise. Heart rate recovery was defined as the decrease in HR from the end of peak exercise to the 1st min of the recovery and cool-down period (peak HR–post-exercise HR). The complete cardiac rehabilitation program was three 20-min periods of cardiovascular exercise on a treadmill per week for 8 weeks (total of 24 sessions). There was 20 min of stretching and calisthenics for warm-up, and the session finished with 20 min of stretching and calisthenics for cool-down; the total duration of each session was approximately 1 hour. The intensity of aerobic exercise was patient-dependent, and increased as tolerated by the patient. Heart rate, blood pressure and exercise intensity were monitored by a senior cardiopulmonary physical therapist during the session. All patients received psychological and dietary counseling. During the psychological sessions, patients were offered coping strategies to accept and live with their cardiac incident. During dietary counseling, they received education on healthy nutrition and were included into a food program.
The 285 subjects who fulfilled the inclusion criteria were grouped on the basis of sessions attended: 5 sessions (group A, n = 149), 10 sessions (group B, n = 72), or all 24 sessions (group C, n = 64). For categorical variables, the differences among groups were analyzed at baseline and after cardiac rehabilitation using chi-squared tests. Continuous variables are expressed as mean ± standard deviation. Pre and post-exercise training parameters were defined as the values at the first session (resting HR I, peak HR I, HR recovery I) and those at the last session attended (resting HR II, peak HR II, HR recovery II). The parameters at the first session were considered the baseline characteristics of the patients. The main outcome measures (resting HR, peak HR achieved during treadmill exercise, end-training HR after 1 min, HR recovery, and change in HR recovery from first to last session) were analyzed and compared using analysis of variance followed by Tukey’s Studentized range test to examine differences among groups if analysis of variance revealed significance. Statistical significance in changes from baseline within groups was evaluated using the paired Student t test. As our patients had incomplete attendance at the exercise training program, univariate analysis was performed to evaluate correlations of HR recovery, age, and ejection fraction with the number of sessions attended. The correlation coefficient of each variable was calculated using multivariate analysis. Analyses were performed using Scientific Package for Social Sciences version 13 (SPSS, Chicago, IL, USA) and SAS version 9.1 (SAS Institute Inc., Cary, NC, USA). Statistical significance was considered when p < 0.05.
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RESULTS
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The completion rate was 19.3%, including patients who completed 24 or more sessions (Figure 1
). The baseline demographic and clinical characteristics of the groups are presented in Table 1. The mean ages of the patients in each group were similar. The risk factors (diabetes, hyperlipidemia and current cigarette smoking habit) except hypertension, ejection fraction, history of coronary artery disease, prior percutaneous intervention, and medications (except antihyperlipidemic agents) were not significantly different among the 3 groups at baseline. Angiographic and angioplasty data (except diffuse lesions) were also similar among groups. Medication profiles are listed in Table 2. Each drug was analyzed separately as a covariate for the change in HR recovery, and no interactions or changes among groups were revealed; the severity of coronary artery disease was similar in each group. Pre and post-training cardiovascular parameters are listed in Table 3. There was no significant difference in the mean resting or end-training diastolic and systolic blood pressure among groups. All 3 groups had similar resting HR, peak HR I, and HR recovery I. Although all groups showed significant improvements in peak HR and end-training HR, there was no significant change in the mean resting HR comparing the first session (baseline) with the last session (follow-up) for each patient (Table 3). A significant group effect on HR recovery II, peak HR II, end-training HR II, and changes in HR recovery was detected, and Tukey’s Studentized range test showed a significant difference among all 3 cardiac rehabilitation groups ( p < 0.0001). Heart rate recovery II correlated significantly with the number of sessions attended (r = 0.626, r2 = 0.392, p < 0.0001; Figure 2). Although the 3 groups were similar in respect of age and ejection fraction, these variables correlated with HR recovery II using univariate regression analysis: r = –0.162, p = 0.001; and r = 0.158, p = 0.003, respectively. In addition, multivariate regression analysis estimated that the number of sessions, baseline ejection fraction and age independently predicted mean HR recovery II (Table 4).
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Figure 2. Linear regression analysis of number of exercise training sessions completed and heart rate recovery after rehabilitation program (HR recovery II). r = 0.626, r2 = 0.392, p = 0.0001.
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Table 4. Multivariate Regression Analysis of Number of Sessions, Ejection Fraction and Age as Predictors of Heart Rate Recovery II
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DISCUSSION
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This historical cohort study showed significant improvements in peak HR and recovery of HR over 1 min after exercise in patients who completed an 8-week cardiac rehabilitation program after PTCA, which is consistent with previous studies.7–13 Improvements were also seen in patients who attended only 5 or 10 sessions. The differences persisted after adjustment for known factors that may affect autonomic tone, including medications and cardiovascular risk factors.
Our patients are recommended to attend phase II cardiac rehabilitation 2 weeks after PTCA, and this program is adjusted for each patient. However, the majority did not complete all 24 sessions of exercise training; of 436 patients undergoing PTCA, only 14.7% attended all sessions. Previous studies have focused on HR variability and baroreflex sensitivity as markers of vagal tone.14,15 Some assessed the effect of cardiac rehabilitation on HR recovery in small numbers of patients with prior myocardial infarction, heart failure, or coronary artery bypass.7–13 To our knowledge, this is the first evaluation of phase II cardiac rehabilitation on HR recovery in a large cohort of patients who had undergone PCTA. Furthermore, we showed a correlation between cardiovascular parameters and other patient characteristics and the number of sessions completed. This study extends current information on HR to patients with coronary artery disease who undergo aerobic exercise training. Comparisons among patient groups revealed that completion of the exercise program significantly increased peak HR, HR recovery II, and the change of HR recovery from 5 to 10, and from 10 to 24 sessions. Also, HR recovery II directly correlated with the number of sessions completed. Heart rate recovery II increased by approximately 1 beat·min–1 on completion of 1 exercise training session. Although previous reports demonstrated that vagal modulation of HR during exercise is independent of age, one study showed that the proportional increase in HR recovery after training in older patients is greater than that found in younger patients, suggesting that older patients derive more benefit from exercise training.16,17 In this study, age had an inverse effect on HR recovery II. Similarly, patients with a lower baseline ejection fraction had less improvement in HR recovery. Furthermore, it may be suggested that these variables are independent predictors of HR recovery II, based on multivariate regression analysis.
The resting HR was similar in each group, and no significant reduction was observed from baseline to follow-up. The improvement of resting HR in the cardiac rehabilitation group may be due to long-term endurance training, which increases parasympathetic activity and decreases sympathetic activity directed to the human heart at rest, thus decreasing resting HR.8,11,18 It was reported that exercise conditioning over a 12-week period improved HR variability, reduced resting HR in cardiac patients, and lowered the risk of sudden cardiac death via increased vagal tone.18 So it might be expected that our patients would not develop any improvement in resting HR after 8 weeks of cardiac rehabilitation. Because concurrent untrained control subjects were not available for this study, it may be argued that the increase in HR recovery observed after PTCA could result from the healing time after a debilitating event rather than an effect of effort training. However, it was shown that after a cardiac event, the sympathetic nervous system is prone to increased activity during the first 3 weeks, whereas the parasympathetic nervous system improves gradually over a 3-month period. It was concluded that time is a factor in the improvement in parasympathetic tone. Both cardiac function and sympathetic nerve activity improve soon after the onset of myocardial infarction, and this improvement is unaffected by exercise training. In contrast, the recovery of parasympathetic nerve activity requires a longer period, along with the recovery of exercise capacity, which is facilitated by even short-term aerobic exercise training.11,19 These observations suggest that improvement in HR recovery during exercise training is not simply a reflection of recovery from debilitating events.
One limitation of this study is its retrospective design with inherent bias. Although HR, blood pressure and exercise intensity were monitored by a senior cardiopulmonary physical therapist, baseline and follow-up exercise stress tests were not performed, and the data were recorded during treadmill exercise training. Nevertheless, these findings seem to be acceptable measures of the exercise stress test. Ideally, the results should be confirmed by a prospective randomized trial, with entry and exit exercise stress testing. Also, because of a lack of data concerning the association between study outcomes and subsequent mortality, this relationship requires further investigation, specifically using a prospective study design. In our study, it was difficult to have a blind control group of patients who would be advised no structured exercise training. Although the benefits of cardiac rehabilitation are compelling and extensive, approximately 15% of eligible subjects completed the formal program. We found that exercise training within a structured program of cardiac rehabilitation correlated with a significant increase in peak HR, HR recovery, and change in HR recovery, regardless of the clinical and demographic characteristics of the patients who had undergone PTCA. The number of sessions attended, baseline ejection fraction, and age were found to be independent predictors of mean post-training HR recovery at the last session.
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ACKNOWLEDGMENTS
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We would like to thank Mahmood Sheikh Fathollahi, PhD, for his biostatistical support for this study. We are grateful to Leila Pirzadeh, MD, for her assistance with data collection. We also thank Mostafa Nejatian, MD, Cardiopulmonary Physical Therapist for his technical support.
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REFERENCES
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ABSTRACT
INTRODUCTION
