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INTRODUCTION
It is known that cardiac rehabilitation programs can improve patients' quality of life and exercise capacity and reduce the rate of heart attack recurrence and mortality.1-5 Cardiac rehabilitation programs traditionally consist of three phases: inpatient, outpatient, and community maintenance.6 Outpatient programs are carefully performed under the supervision of health care providers with monitoring based on exercise tolerance test results. Despite the numerous benefits of cardiac rehabilitation programs, the participation rates still remain very low,7 and it has been suggested that this is due to patients' difficulties and problems with medical services.8 Several obstacles that can impede patient participation have been reported, including occupational and domestic issues, a lack of interest in rehabilitation, a reluctance to make lifestyle changes, depression, or a lack of family cooperation.9-13 In our previous study, it was found that one of the foremost barriers to participation was the lack of awareness of rehabilitation programs (78%). Other barriers included the patients' doubt of positive effects, a lack of time, fear, high cost, poor physical condition, and poor accessibility to program centers due to distance and traffic problems. The lack of awareness and the patients' regional or socioeconomic conditions were particularly responsible for rehabilitation discontinuation.14
Community-based self-exercise programs can be primarily applicable to patients with a low risk of heart attack if they sufficiently understand the significance of cardiac rehabilitation, but they have difficulty accessing the programs due to their regional and socioeconomic problems. It is expected that self exercise programs will be beneficial for patients who cannot attend supervised exercise programs in hospitals. For successful performance, the program should be designed to improve the exercise capacity of patients with coronary disease as supervised programs do, and the program should include only patients with a low rate of cardiovascular events. After demonstrating efficacy and safety, self exercise programs can be used for a wide range of patients, and these programs can improve their cardiopulmonary function. Therefore, these programs will be more cost-effective and have better effects on reducing the recurrence of heart attack and the mortality rate. We aimed to compare the results of self-exercise programs and supervised programs for 6 to 8 weeks after screening and selecting low-risk patients.
MATERIALS AND METHODS
Study subjectives
We enrolled patients who were admitted to our cardiovascular center with acute coronary syndrome (ACS) between January 2007 and December 2008, or those who were referred to the cardiac rehabilitation clinic after undergoing percutaneous coronary intervention (PCI) or a coronary artery bypass graft (CABG). The exclusion criteria included prior PCI or CABG; left ventricular ejection fraction (LVEF) less than 40%, uncontrolled arrhythmia, hypertension, or diabetes; as well as additional issues that would preclude a potential patient from participation in the program.
All the eligible patients were recommended to participate in cardiac rehabilitation programs by means of educating them about the benefits and contents of the programs. The patients who notified us of their intention to attend were assigned into the supervised exercise group. Those who were not able to present in the hospital were assigned into the self exercise group if they were categorized as "low-risk" according to the Risk Classification for Exercise Training, as established by the American Association of Cardiovascular and Pulmonary Rehabilitation (AACVPR) (Table 1).15
We followed 91 patients; 45 patients were assigned into the supervised exercise group and 46 were assigned into the self exercise group. The supervised exercise group was composed of 38 men (84%) and 7 women (16%), and the self exercise group was composed of 38 men (83%) and 8 women (17%). There was no significant difference in the gender distribution between the two groups. The mean age was 57.6 in the supervised group and 57.4 in the self group; the mean age was not significantly different. In addition, there was no significant difference in the rate of patients who underwent PCI or CABG, the number of affected coronary arteries, the LVEF at baseline, and the maximal oxygen consumption (VO2max) in both groups (Table 2).
Method
Echocardiographic studies were performed within 48 hours before and after PCI in all the patients, and symptom-limited exercise tolerance testing was carried out using the modified Bruce protocol within a week after discharge from the hospital. A real-time recording 12-channel ECG (Q4500, Quinton Instrument Co., Boston, USA), a respiratory gas analyzer (QMC, Quinton Instrument CO., Boston, USA), an automatic blood pressure and pulse monitor (Model 412, Quinton Instrument Co., Boston, USA), and a treadmill (Medtrack ST 55, Quinton Instrument Co., Boston, USA) were included in the test. The VO2max was measured with a respiratory gas analyzer and the maximum heart rate, the stable heart rate, and the myocardial oxygen demand (MVO2) were estimated by the ECG and the automatic blood pressure and pulse monitor. The MVO2 was calculated by multiplying the systolic blood pressure and heart rate as the rate pressure product (RPP). The submaximal MVO2 was measured at the end of stage 3 of the modified Bruce protocol.
The patients in the supervised group were monitored with an ECG based on the results of exercise tolerance testing during the program in the hospital. A Quinton MEDTRACK SR60 Treadmill (Quinton Instrument Co., Seattle, USA) and a Quinton CORIVAL 400 ergometer bicycle (Quinton Instrument Co., Seattle, USA) were used in the program. The exercise intensity was increased in a stepwise manner based on the target heart rate. The target heart rate was supposed to be 40% to 85% of the value of the heart rate reserve, which can be calculated with the maximum heart rate and stable heart rate obtained from exercise tolerance testing. The supervised exercise programs were mostly of a 6- to 8-week duration, three sessions per week with a total of 50 minutes per session. Each exercise session was divided into a 10-minute warm-up, 30 minutes of prescribed exercise, and a 10-minute cool-down. After completing the program, we advised the patients to participate in self exercise programs based on their target heart rate and the rate of perceived exertion obtained from re-tested exercise tolerance. The patients in the self group were prescribed exercise based on the results of the exercise tolerance testing performed within a week after discharge, and they were advised to participate in community-based self exercise programs for 6 months without a period of supervised training. The prescribed exercise included fast walking, power walking, bicycling, and jogging, depending upon the individual's exercise capacity and systemic conditions.
Information on risk factors and therapy was given to all the patients and their families. They were also counseled for smoking cessation, obesity, and nutrition, and we monitored their adherence to exercise and risk factor management with blood tests, body fat, and blood pressure measurements, in addition to exercise counseling every 1 to 3 months. Symptom limited exercise tolerance was re-tested in both groups using the modified Bruce protocol after an initial 6-month period of the programs. The extent of improvement and the pattern of cardiopulmonary capacity were compared between the two groups at baseline and 6 months. Severe cardiovascular complications during the study period were also investigated.
Statistical analyses
The data was statistically analyzed with SAS Enterprise Guide 4.1 (4.1.0.471). We used Chi-square tests to compare the gender distribution and the rate of PCI and CABG, and the Wilcoxon rank sum test was used to compare ages, the LVEF, the VO2max, the maximum heart rate, the stable heart rate, and the maximal and submaximal MVO2 at baseline and 6 months. The Wilcoxon signed rank test was used to compare the VO2max, the maximum heart rate, the stable heart rate, and the maximal and submaximal (Phase III exercise) RPPs in each group at baseline and 6 months. A p-value<0.05 was considered statistically significant.
RESULTS
Severe cardiovascular complications during exercise
According to the AACVPR, 18 of 45 patients had high-risk factors on the risk classification for exercise training in the supervised group, whereas none of the 46 patients in the self exercise group had high-risk factors (Table 1). Severe cardiovascular complications did not occur in either group during the study.
Comparing the amount of cardiopulmonary capacity change
In the supervised group, the VO2max and maximum heart rate increased while the stable heart rate and submaximal MVO2 decreased significantly compared to baseline. Similarly, the VO2max increased and the submaximal MVO2 decreased in the self exercise group, but no significant change in either the maximum heart rate or stable heart rate was observed. The maximal MVO2 tended to decrease in the supervised group, and it increased in the self group, but these changes were not statistically significant (Table 3).
Comparing the rate of change of cardiopulmonary capacity
There was no significant difference in the rate of maximum heart rate change, the stable heart rate, and the maximal and submaximal MVO2 between the two groups. The rate of change of the VO2max increased more significantly in the supervised group than that seen in the self group (21% vs. 8.6%, p<0.05) (Table 4).
DISCUSSION
Coronary artery disease has a high prevalence and high mortality rates all over the world. Due to advances in medical technology, the mortality rate seems to have diminished, but the prevalence rate has gradually increased.16-18 It has been demonstrated that cardiac rehabilitation programs, such as those that include exercise programs, nutrition counseling, smoking cessation programs, pharmaceutical therapy, and weight control, play a key role in improving exercise capacity and secondary prevention for patients with coronary artery disease.19,20 In a meta-analysis of 48 randomized clinical trials, it was found that cardiac rehabilitation programs reduced the all-cause mortality by 20% and the cardiovascular mortality by 27%.21,22 Despite these benefits, cardiac rehabilitation programs have been underused, and the rate of discontinuation is very high. Many reasons for the low participation rates have been reported, such as poor access to hospitals23-25 and the lack of time due to occupational or household work.26-29 A self exercise program was first introduced at the beginning of the 1980s. It can be an alternative to traditional programs, and it has been extensively used for patients due to its easy accessibility and convenience.30
Exercise training is a critical component of cardiac rehabilitation programs. Aerobic exercise can reduce the myocardial burden when performing daily physical activities because aerobic exercise increases the VO2max and it decreases the submaximal heart rate.31-33 In addition, the VO2 in the systemic muscles may be reduced, and as these muscles are needed to exercise with the same intensity, reduction in the VO2 lessens the myocardial burden in patients with heart disease. The incidence of myocardial ischemia can be reduced by decreasing the MVO2 because myocardial ischemia generally occurs at the same RPP. We suggest that improvement of cardiopulmonary capacity was achieved in both groups because the VO2max increased and the submaximal MVO2 decreased. Consequently, this relieved the patients' cardiopulmonary symptoms, and enhanced functional capacity may be expected in daily and socio-occupational activities.
Several foreign reports that have published the results of comparative studies on the improvement of exercise capacity with supervised and self exercise programs, the management of risk factors, and the quality of life. According to the recent Cochrane meta-analysis, no difference was observed in cardiopulmonary exercise capacity, risk factors management, health-related quality of life, and recurrence of heart disease (death, reperfusion, and readmission) between supervised and self exercise programs during short term and long term follow-up.34 Jolly et al.30 reported that exercise capacity, systolic blood pressure, and total cholesterol were improved more in the supervised group, but no statistically significant difference was seen. In our study, the VO2max significantly increased and the MVO2 significantly decreased both in the supervised group and the self group; however, statistically significant increases of the maximal heart rate and significant decreases of the stable heart rate were found only in the supervised group. Specifically, the change rate of the VO2max was greater in the supervised group (p<0.05). One possible explanation for this is that the exercise compliance was much greater in the supervised group than in that of the self group even though the patients were closely monitored and guided. Furthermore, it is already known that the lower the functional capacity is, as measured before initiating cardiac rehabilitation programs, the greater the improvement may be after completion of the programs.
However, safety and legal parameters concerning prevention of heart attack are not currently established; therefore, self exercise programs should be carefully used. Patients should always be tested to determine whether they are eligible for the programs by evaluating the risk of cardiac attack with exercise tolerance testing. Severe cardiovascular complications associated with exercise did not occur in any of our patients. A possible explanation is that the 18 patients with a high risk of heart attack were assigned into supervised programs, whereas no high-risk patients were assigned to the self exercise group. Moreover, the patients in the supervised group had their exercise intensity controlled in real time by close monitoring at the beginning of each exercise session.
There are some limitations in our study. First, this is not a randomized comparative study. The patients decided to participate in cardiac rehabilitation programs by themselves, and the patients at a high risk of heart attack during exercise were excluded from the self exercise group. Second, we did not clearly determine differences in the management scores of several risk factors in both groups, including hypertension, diabetes mellitus, hyperlipidemia, obesity, and smoking cessation. Finally, long-term follow-up after 6 months was not done. Additional studies may be necessary to compare the improvement in cardiopulmonary functional capacity with long-term exercise as well as the recurrence of heart attack and mortality rates and cost-effectiveness.
CONCLUSION
We performed 6-month cardiac rehabilitation programs for patients with prior PCI or CABG due to coronary artery disease. We demonstrated that cardiopulmonary exercise capacity significantly improved in both groups. However, the change of the VO2max, maximum heart rate, and stable heart rate improved more in the supervised exercise group than in the self exercise group. Further large-scale, long-term follow-up studies will be required in the future.
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