| Abstract|| |
Background and Purpose: Cardiovascular disease, especially coronary artery disease, is the most common cause of death in the world. Cardiac rehabilitation (CR) is provided to improve the effectiveness and decrease the side effects of coronary artery bypass grafting (CABG). This study was performed in 2014 in the CR center of Ekbatan hospital, Hamadan, Iran, to compare the double product (DP) index before and after CR in patients undergoing CABG. Materials and Methods: In this study, 100 patients visiting the center, who underwent CABG 2 months earlier, were studied. The exercise tolerance tests (ETTs) were conducted before and after the rehabilitation sessions for everyone, and the maximum heart rate and systolic blood pressure of them during the ETT were collected at their peak level. Results: In general, the mean of the DP index showed a significant increase after rehabilitation compared to before it (P = 0.05). Furthermore, the mean comparison of this index based on the independent study variables showed that the increase of the mean of the DP index after rehabilitation in men in both the age groups of below and above 60-year-old, in nondiabetic patients, in people with high blood lipids, people with normal blood lipids, patients with moderate degree of left ventricular dysfunction (EF = 30–44), people with relatively normal left ventricular function, smokers and nonsmokers, as well as individuals with no history of high blood pressure, was significantly different. Conclusion: The results of this study showed that the mean of the DP index which is a quantitative criterion for the assessment of cardiac function, significantly increased after 12 rehabilitation sessions in patients who underwent CABG.
Keywords: Cardiac rehabilitation, cardiovascular disease, coronary artery bypass graft, double product index
|How to cite this article:|
Moradi M, Fariba F. A comparative study of the double product index before and after cardiac rehabilitation in patients undergoing coronary artery bypass grafting. Ann Trop Med Public Health 2017;10:950-5
|How to cite this URL:|
Moradi M, Fariba F. A comparative study of the double product index before and after cardiac rehabilitation in patients undergoing coronary artery bypass grafting. Ann Trop Med Public Health [serial online] 2017 [cited 2019 Oct 17];10:950-5. Available from: http://www.atmph.org/text.asp?2017/10/4/950/215872
| Introduction|| |
Cardiovascular diseases are one of the most common causes of death across the world and in terms of mortality rate, morbidity, disability, and economic costs, it is announced as the most important cause of death until 2020. Here, coronary diseases are of the most common heart problems. In addition to pharmaceutical methods, the method of choice for the treatment of coronary artery disease (CAD) is revascularization, and coronary artery bypass grafting (CABG) is a revascularization method. More than 8 million, CABG is performed across the world every year, and almost 40,000 open heart surgeries are performed in Iran. Of the most important actions to increase the effectiveness of heart surgery and decrease its side effects, is cardiac rehabilitation (CR). After CABG is performed, the patient's pharmaceutical treatment is continued and CR (as secondary prevention) which plays a very important role among additional nonpharmacologic treatments  is performed to improve the patient's sociopsychological state, limit the somatic and psychiatric effects of cardiovascular disease, reduce the risk of sudden death or the reoccurrence of heart attack, control the symptoms of CAD and stabilize or reverse the disease process of atherosclerosis. Here, physical exercise is the main component of a rehabilitation program, which increases patients' ability in performing their daily activities. Key physiological effects of exercise on cardiac patients include the reduction of heart rate (HR) followed by longer time for blood filling of the heart and coronary arteries in the diastolic phase. Also, due to the production of more ATP in the breathing path after the aerobic exercise, the acidosis level of lactic increases less. Therefore, respiratory effort is decreased, and subsequently lower respiratory stress is created. Consequently, the patient feels physically stronger and more active.
One of the first actions in CR program is the ETT, which is a basis for determining the duration and intensity of exercises in every session. Double product (DP) is an indirect measurement criterion for determining the myocardial oxygen demand. The peak of the DP can be used to specify cardiovascular performance. In most normal people, the peak of the DP reaches 25–30 mmHg × beat/min × 10−3. In many patients with significant ischemic heart disease, it is uncommon for the DP to exceed 25 mmHg × beat/min × 10−3. Therefore, it can be said that DP is an acceptable criterion in the cardiac performance assessment of patients.
Staky et al. (2011) investigated the effect of CR on the improvement of the hemodynamics state in patients after CAGB. Their study showed that a group of patients who underwent rehabilitation sessions, compared to the control group, showed a significant improvement in hemodynamic response to exercise and CR has specifically improved the performance of these patients. According to this study, it was recommended that patients be referred to a rehabilitation center after CABG. In a study performed by May and Nagle, rate pressure product which is the same as DP, after physical exercises in people with CAD, was studied and it was shown that the DP significantly increases in CAD patients who undergo regular maximal exercise (P < 0.1) whereas the DP in people who underwent submaximal exercise, decreases (P < 0.1). Based on the results of this study, it is recommended that physiological changes occurring after aerobic exercise in skeletal muscle and myocardium, play a role in improvement the symptoms and increasing the maximum activity capacity of patients with CAD. Suaya et al., performed a clinical research in the USA with the title of CR and the survival rate in adult patients with CAD. The results of the study also showed that participation in a CR program decreases the mortality rate in patients. The mortality rate of 21%–34% in a society participating in the CR program was lower than the society who did not participate. Similarly, Martin et al. investigated the CR in patients with CAD, and their study results showed that completion of CR session in CAD patients, improves their survival and decreases their inpatient admission rates. In a study, performed by Kirk et al. to assess and assess the feasibility of the effects of a CR standard program in decreasing the risk factors in patients after a heart stroke and transient ischemic attack, it was shown that a significant improvement was created in the physical activity level of the group undergoing the CR program compared to the control group. Based on the results of this study, the standard CR program, is effective at decreasing the risk factors for cardiovascular events in patients after a heart stroke and transient ischemic attack. A study performed by Saeidi et al. in 2013 to investigate the effect of CR program on the quality of life of CAD patients, showed that after eight CR sessions, the quality of life of the patients (including physical performance, physical limitation, volatility, and body pain) significantly improved. In a study performed by Siavashi et al. to determine the effect of CR on the hemodynamic indices of patients undergoing CABG in 2011 showed that the average HR after 12 CR sessions, is significantly less compared to the control group. However, in the other study parameters including systolic blood pressure (SBP), diastolic blood pressure, mean arterial blood pressure, and pulse index and arterial oxygen saturation, no significant difference existed. In 2011, Rocha et al. in a study, investigated the relationship between age and the physical response, performance, and sociopsychological response to the CR program and the results of the study showed that participation in the CR program, significantly improved the cardiovascular risk profile, functional capacity, and quality of life of the patients regardless of their age. Therefore, it is recommended that adult patients participate in the CR program.
Given the ever increasing rate of CAD and its side effects in societies which causes death, inability, and disability among a great portion of the working force and the great treatment costs, and also the ever increasing age of patients, it becomes necessary to provide a CR program to improve the results from CABG, reduce future cardiovascular events and improve lifestyle. Since the majority of studies have investigated the effect of rehabilitation on the quality of life and patients' physical ability, it becomes necessary to perform studies about the acceptable indices in the assessment of cardiac muscle function to show the effect of rehabilitation in determining the prognosis. Therefore, since the DP is an acceptable quantitative criterion in the assessment of cardiac muscle function, the purpose of this program is to compare the DP index before and after 12 CR rehabilitation sessions in post-CABG patients, through the use of the Bruce method (standard exercise tolerance test [ETT] protocol).
| Materials and Methods|| |
This study was performed on 100 patients who visited underwent CABG in 2014 at the Ekbatan hospital of Hamadan and had the indications for participation in the CR program. The exclusion criteria included congenital deformities of the skeletal system, acquired defects, musculoskeletal disorders, and any reason which prevented the completion of the rehabilitation program in patients.
The patients referred to the rehabilitation unit, who had undergone CABG 2 months earlier, were studied as follows: before the CR program, they underwent the ETT via the Bruce method and then according to standard and similar protocols, they underwent 12 rehabilitation sessions. After the completion of the sessions, the ETT was conducted on patients again. During the ETT and before and after rehabilitation, at the peak level, when a patient gained maximum HR, the SBP of the patient was measured and registered. For all the study patients, a checklist containing the information required for the research including the HR maximum, peak SBP, age, gender, diabetes, hypertension, dyslipidemia, and smoking condition was considered which was completed using the information registered in every patient's profile at the rehabilitation center. The resulting data were analyzed through the SPSS software developed by IBM cooperation in London.
| Results|| |
Of the total 100 patients who entered the study, 63 were male (63%) and 37 were female (37%). The average age of the study patients was 60 ± 5.5. The average peak systolic pressure and average HR maximum, before and after rehabilitation sessions were measured [Table 1] and it was discovered that the SBP of the study patients, after the CR does not show a significant difference compared to before the CR (P = 0.41). Whereas the average HR maximum of the study patients did show a significant statistical increase after CR compared to before it (P = 0.00) [Table 1].
|Table 1: Comparison of the average of patients' systolic blood pressure peak, heart rate maximum, and double product index before and after cardiac rehabilitation|
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The value of the DP was calculated using the information obtained from the systolic pressure and HR based on a formula. Accordingly, the average of the DP index before and after rehabilitation was 17900 ± 4048.2 and 19800 ± 3620, respectively. Moreover, it was shown that statistically, the mean of the DP index in the patients, is significantly higher after rehabilitation than before it [Table 1]. But by comparing the average of the DP index based on patients' gender, it was discovered that the value of this index significantly differs in men after rehabilitation than before it, but it is not significantly different in women [Table 2]. In addition, the mean of the DP index of the patients after rehabilitation in both age groups of below and above 60-year-old, significantly increased [Table 3]. The average of the DP index of patients, before and after rehabilitation in people with diabetes, did not show a significant statistical difference, whereas, in nondiabetic patients, it significantly increased after rehabilitation [Table 4]. The results of this study also showed that the average of the DP index of patients before and after rehabilitation in people with high blood lipid, people with normal blood lipid, patients with moderate degree of the left ventricular dysfunction (EF = 30–44), people with relatively normal left ventricular function, smokers and nonsmokers as well as individuals with no history of high blood pressure, is statistically significantly different, whereas in people with high blood pressure, this index does not show a significant difference before and after rehabilitation [Table 5],[Table 6],[Table 7],[Table 8].
|Table 2: Comparison of the average of patients' double product index before and after cardiac rehabilitation based on gender|
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|Table 3: Comparison of the average of patients' double product index before and after cardiac rehabilitation|
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|Table 4: Comparison of the average of patients' double product index before and after cardiac rehabilitation based on the existence or lack of diabetes mellitus|
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|Table 5: Comparison of the average of patients' double product index before and after cardiac rehabilitation based on the existence or lack of dyslipidemia|
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|Table 6: Comparison of the average of patients' double product index before and after cardiac rehabilitation based on high blood pressure|
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|Table 7: Comparison of the average of patients' double product index before and after cardiac rehabilitation based on smoking|
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|Table 8: Comparison of the average of patients' double product index before and after cardiac rehabilitation based on left ventricular dysfunction degree|
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| Discussion|| |
CADs are the most common heart problems in the world. The only way to treat the patients and increase their lifetime in most cases is CABG. Of the most important actions to increase the effectiveness of heart surgery and decrease its side effects is CR. This study was performed to compare the average of the DP before and after CR in patients undergoing CABG.
Based on the data of the present study, the average of the DP index after CR in patients significantly increased but no significant difference existed between the average of SBP peak of the patients before and after rehabilitation. These findings are in agreement with the research results of Siavashi et al. (2013) because they also showed that the SBP of patients undergoing rehabilitation after CABG does not significantly change compared to the control group. Since a patient's heart medicines are not discontinued during rehabilitation and exercise test, and since the resistance and cardiovascular tone of the patient is mainly due to the effects of the medicines, so, it is not expected that the peak of SBP significantly increases but in this study, it was observed that the average maximum of HR of the patients significantly increases after rehabilitation compared to before it. Reaching a higher HR in a similar SBP shows an improvement of cardiac function and an increase in the capacity of patients' activity for reaching a higher HR during exercise after rehabilitation.
In this study, the DP index in patients significantly increases after rehabilitation compared to before it. Similarly, in a study by May and Nagle also, the DP index significantly increased in CAD patients undergoing maximal exercise and regular aerobic exercises. In this study, the average of the DP index significantly increased in men after rehabilitation compared to before it, but in women, it did not significantly change. One reason for it can the lower activity capacity in the female patients. Furthermore, due to the greater prevalence of diastolic dysfunction in women, during similar activities, the left atrial filling pressure has a higher increase in them compared to men, which subsequently causes increased pulmonary wedge and shortness of breath, followed by faster termination of physical activity in women.
In contrast to nondiabetic patients, the increase of the average of the DP after rehabilitation compared to before it in diabetic patients was not statistically significant. This result is not surprising because probably, due to the prevalence of autonomic neuropathy in diabetic patients, during similar activities, these patients have a lower capability at increasing their HR. Also, since diabetes increases heart muscle size, the rate of ventricular function of this patient decreases and consequently the patient's response to indicators effective at cardiac function compared to normal people decreases. Wasserman et al. in their study showed that in diabetic patients, particularly women, the sustainability of the postrehabilitation cardiorespiratory fitness changes is not as good as that of nondiabetic people. Vergès et al. stated in 2004 that the exercise capacity in patients after an ischemic event is significantly lower and it seems that blood sugar levels in diabetic patients, affects the response to CR. In patients with no history of high blood pressure, the average of the DP index after rehabilitation increased significantly compared to before it, but in patients with a high blood pressure, no significant increase was observed. This result was predictable because due to the known effects of high blood pressure at creating left ventricular hypertrophy and subsequently a higher diastolic dysfunction and left atrial filling pressure, even in people with no history of CAD who have a high blood pressure, the HR reserve increase during exercise compared to those with normal blood pressure is lower. Therefore, in patients with normal blood pressure, due to the more appropriate response of these patients' heart to physical exercise, the DP index shows a greater increase after rehabilitation compared to people with a high blood pressure.
The increase of the average of the DP was clearer in the age group of below sixty, which can be due to their higher physical ability at following the rehabilitation programs. Moreover, based on the formula (maximum HR: 220-age), with increased age, the maximum HR decreases. Consequently, in a similar activity, older people gain a lower HR. Given the direct effect of the maximum HR at calculating the DP index, the difference is justifiable. The average DP after rehabilitation compared to before it in both age groups with EF: 30–44 and EF >45 was higher, and was statistically significantly different, which can show that decreased cardiac function does not have any effect of the positive results of the rehabilitation program and both age groups in this study benefited from it.
| Conclusion|| |
Based on the results of this study, the average DP index after 12 CR sessions significantly increased in the patients. In general, it can be said that the CR program in patients undergoing CABG, has a positive effect of their cardiac muscle function.
Given the ever increasing growth of cardiovascular diseases, a greater attention to the issue of CR in research, more study in the field of the investigation of quantitative and reliable criteria in this area, conducting more extensive studies with greater sample sizes and finally investigation of the rehabilitation effects in various heart diseases in patients with cardiac angioplasty, valvular heart disease and heart failure, can show the importance and role of rehabilitation at increasing the health and empowerment of people with atherosclerosis complications and play a significant role at increasing the quality of life of cardiovascular patients.
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Conflicts of interest
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Department of Cardiology, Farshchian Hospital, Medical University of Hamadan, Hamadan
Source of Support: None, Conflict of Interest: None
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]