Congestive heart failure (CHF) is one of the most prevalent pathologies in the United States. In adults aged 65 to 74 years, 60% of men and 40% of women are diagnosed with CHF.1 Between 1993 and 2003, deaths from CHF increased 20.5% while the overall death rate actually decreased by 2%.1 The disease process of CHF leads to multiple body system changes. These changes include impaired left ventricular function, baroreflex desensitization, impaired vasodilatory capacity, type I muscle fiber atrophy, decreased muscle fiber cross-sectional area, and dyspnea.2–6 Prior to the 1970s, it was recommended for patients with CHF not to perform any aerobic or resistance exercise beyond daily functional needs. The medical community believed that the added stress created by exercise on an already compromised heart posed significant risk of mortality. However, in the 1970s, researchers began to examine the effect of low-level aerobic exercise in this population.7–9 The results of this early research were recommendations to use low-intensity walking or bicycle ergometry in the management of patients with CHF.7 Subsequent research led to specific guidelines for aerobic exercise2,3,10–14 and resistance exercise for individuals with CHF.3,6,11–13,15,16
In 2001, the American Heart Association issued standards for exercise testing and training,4 followed by a similar statement from the German Federation of Cardiovascular Prevention and Rehabilitation in 2004.17 These recommendations were determined by a body of experts reviewing the scientific literature. However, in reviewing research studies completed to date, it is evident that studies examined different modes, intensity levels, and durations of exercise. The interpretation of these findings is further complicated by the varied inclusion criteria, parameters of exercise, and the heterogeneity of patient populations. Systematic reviews have not rated the strength of the evidence examined, nor have they provided a complete view of aerobic and resistance exercise prescription in CHF.2,5,16–19 There was also a meta-analysis done with progressive resistance exercise, but it only examined blood pressure (BP) levels.15
This review provides an examination and synthesis of research of aerobic and resistance training in patients with CHF using only randomized control trials (RCTs) and controlled clinical trials (CCTs). This review only includes studies with clinically relevant results. To this end, it is noted that in analyzing the literature, statistical significance of an intervention did not necessarily translate to clinical importance. The purpose of this study was to identify the strength of evidence supporting use of therapeutic exercise interventions in patients with CHF, using a modified Philadelphia Panel system critical review of research rating methods.20 Findings were then used to either validate existing guidelines or provide recommendations for changes in current practice, considering study design, statistical significance, and clinical importance.
For this critical review of research evidence, a computerized literature search was conducted using electronic databases including MEDLINE, CINAHL, and the Cochrane Controlled Trials between 1990 and January 1, 2006. Because computer searches may not include all relevant studies, the reference lists of included trials, expert body recommendations, and literature reviews were also searched for additional relevant studies. Study inclusion criteria for the critical review of the literature included (a) only studies using RCT or CCT study designs, (b) clinical subjects from populations of individuals with either CHF or coronary artery disease (CAD), and (c) studies that evaluate effects of either aerobic exercise or strength training exercise.
The Philadelphia Panel study rating system20 was used to judge the strength of individual studies. This rating system was employed because it considers rigor of study design as well as both the clinical and statistical significance of results. The Philadelphia Panel study rating system was developed to be used for the establishment of practice guidelines based only on the strongest study designs and clinically important results. The Philadelphia Panel sets high standards in an attempt to ensure true efficacy of intervention outcomes for the establishment of practice guidelines. When establishing practice standards, a study's outcomes were analyzed for efficacy and generalization. The Philadelphia Panel system rates studies using a 4-point scale (A, B, C+, and C). The strength of study rating system is shown in Table 1. The published Philadelphia Panel report also devised a rating system that can be used to judge the strength of a collective body of evidence. The system first determines whether the intervention produced a statistically significant benefit. Clinical importance is then determined by evaluating the absolute benefit of the outcome and the relative difference between intervention group and control group. A relative difference of at least 15% is deemed clinically important. Outcomes that are not statistically significant are noted. If no data exist for a specific intervention, then no grade is given. The description of the strength and level of evidence of each intervention examined in this study are shown in Table 2.
Although exercise recommendations for persons with CAD have long been established, studies reviewed in this analysis focused on exercise interventions in persons with CHF. The outcomes examined were BP, maximum oxygen consumption (v̇O2max), resting heart rate (HR), left ventricular function, peak lactate levels, dyspnea (measured via CHF breathlessness questionnaire), work capacity, muscle strength as measured by muscle, and muscle endurance. These outcomes were examined because they were the most commonly evaluated outcomes in the literature related to patients with CHF. Interventions assessed were resistance exercise and treadmill and bicycle ergometer aerobic exercise. Studies of healthy persons, patients with CAD or chronic diseases other than CHF, patients undergoing a stretching program, or those who performed no exercise were included as control groups. In each study, the control group was found to be comparable with the exercise group in both demographic and clinical data.
The electronic search for exercise, CAD, and heart failure resulted in 6,586 citations. After narrowing the search to aerobic and resistance exercise in patients with CHF, there were 208 citations. Of these, 20 were isolated for full review on the basis of population, basic design, and outcomes measured. Of the 20 clinical trials reviewed, only 6 met the study inclusion criteria of either an RCT or a CCT study design (Table 3). There were also 5 literature reviews,2,5,16,18,19 2 recommendations of expert bodies,4,17 and 1 meta-analysis.15 These studies were not included in the final analysis, as they did not rate the high level of study design and rigor needed for inclusion. One older study21 was referenced in several of the reviewed studies, as it was one of the earliest to examine the role resistance exercise. This study was reviewed but not included in the final analysis because of the characteristics of the patient population and length of time since the research was conducted.
Aerobic and resistance training were analyzed independently so as to provide clinical benefit. The following results show the outcome measures that each mode of training effected (Table 4).
Three RCTs (N = 166) were included on the basis of Philadelphia Panel review criteria. These studies examined the effects of aerobic cycle ergometry in comparison with a control group. One study using a single cohort design was analyzed but not included in this evaluation because of lack of randomization and control group. One study of RCT design was analyzed, but results were not included because of lack of statistical and/or clinical significance.
Clinically important benefits (shown as percentage of outcome improvement) and statistically significant results (P values) were found for the outcomes of v̇O2max (18%, P < .01; 25%, P < .001; and 19%, P < .001), dyspnea (56%, P < .01), work capacity (54%, P < .01; and 24%, P < .001), and left ventricular function (16%, P < .01) in the aerobic exercise treatment group in comparison with the control group of rest or no exercise (Table 5).10,12,14 Resting HR and submaximal exercise HR effects were statistically significant but were not shown to have clinical importance (Table 6).10,12
Clinical Recommendation in Comparison With Other Guidelines
This review found good evidence (level 1, RCTs) for use of aerobic bicycle ergometer exercise to increase v̇O2max, work capacity, and left ventricular function and decrease dyspnea in patients with CHF. This recommendation is consistent with other guidelines or recommendations made by expert bodies.4,17,19
Three RCTs (n = 47) were included in the analysis of resistance exercise. Four studies had been excluded because they lacked a control group. One meta-analysis was reviewed, but it was excluded as it did not include only RCTs or CCTs.
This analysis demonstrated clinical importance (shown as percentage of outcome improvement) and statistical significance (P values) for improvements in left ventricular function (29%, P = .0085), peak lactate levels (27%, P = .064), muscle strength (44%, P < .016; and 25%, P < .05), and muscle endurance (64%, P = .001).3,6,10,12,14,22 The results for left ventricular function and peak lactate levels occurred in a group that participated in bicycle ergometer and progressive resistance training in comparison with a control group of just bicycle ergometer training.3 Muscle strength and endurance results were derived from a progressive resistance training program in comparison with a placebo group of low-intensity stretching.6 Another study also demonstrated increased muscle strength with maximal resistance exercise of 1 muscle group of 1 limb in comparison with no exercise of the same muscle group of the contralateral limb (Table 5).22 One study (n = 20) showed statistically significant increases in v̇O2max and work capacity with resistance exercise, but there was no clinical importance on the basis of percentage of improvement (Table 6).3
Clinical Recommendation in Comparison With Other Guidelines
This review found good evidence (level 1, RCTs) to perform progressive resistance exercise with patients with CHF. Although each study utilized a different protocol, the programs were comparable in their use of muscle groups and resistance training intensities. Resistance exercise was shown to improve left ventricular function, peak lactate levels, muscle strength, and muscle endurance. There have been a number of studies and reviews of resistance exercise in patients with CHF. However, many of the studies performed were not of an RCT or a CCT design, so outcomes are based on single case groups only. The results of this analysis do correspond with recommendations made by bodies of experts or are based on other systematic reviews of the literature.4,11,13,15–18,21 These literature reviews and published recommendations were not included in this analysis on the basis of failure to meet the criteria for this review.
Interventions With Insufficient Data
For aerobic exercise, 1 RCT (n = 17) was included for the outcome of resting HR.10 The exercise group performed bicycle ergometer training in comparison with a control group of rest or no exercise. A decrease in resting HR was shown, but the decrease was not statistically significant. One RCT (n = 49) was included for v̇O2max and dyspnea.23 Exercise consisted of bicycle ergometer training in comparison with a control group of rest or no exercise. Dyspnea and v̇O2max improved in the exercise group, but they were not statistically significant in comparison with the control group.
This analysis thoroughly examined research studies for outcomes related to aerobic and resistance training in patients with CHF. Four outcomes were found to have evidence demonstrating significant clinical improvements after aerobic exercise as well as after resistance exercise.
There are limitations to this analysis, as with any other study or review. The method of patient randomization was not the same in each of the studies, and none of the studies were blinded. Many studies reviewed lacked a control group, so the number of studies meeting the inclusion criteria was low. The use of different protocols for aerobic and resistance training could have lead to variations in the coordination of data between studies. Publication bias to publish only studies with positive results could exaggerate treatment effect. However, because this patient population is a large percentage of the general population, publication bias is believed to be less of a factor than it may be in other patient populations. Each of the studies included in the analysis used small sample sizes, so this may have affected the overall power of these findings. Lastly, databases utilized in this search were restricted to the English language. However, to help address this limitation, reference lists of each study reviewed were utilized to potentially identify other studies for review.
Traditionally, patients with CHF have been instructed to limit exercise and activity. There has been an increase in research in this patient population, but studies use various protocols and research study designs. Several reviews of the literature have been completed, but these reviews have included a variety of study designs. They have also failed to evaluate clinical importance. This analysis utilized strict inclusion criteria of RCT- and CCT-only outcomes that were statistically significant and clinically important. Because of the rigor of the Philadelphia Panel system, the results of this study have shown efficacy for exercise interventions in patients with CHF. Although the number of studies included in the final analysis was small, the results of this analysis can be useful in the application of therapeutic exercise interventions for patients with CHF. The small number of studies meeting these criteria demonstrates a need for further research utilizing strict study design.
APPLICATION TO PRACTICE
Aerobic exercise using a bicycle ergometer was shown to have clinical importance in the outcomes for levels of dyspnea, work capacity, and left ventricular function. While 1 study used the 6-minute walk test as a measurement tool,14 structured walking was not part of any exercise protocol. Therefore, the guidelines established here can only be applied to bicycle ergometer exercise. Further research should be performed using strict study design to evaluate efficacy of other forms of aerobic exercise. The 3 RCTs were of good quality and were performed with patients with NYHA classes I–III CHF.10,12,14 Findings indicate that bicycle ergometer exercise is effective in each of these 3 classes. These studies did not examine patients with NYHA class IV CHF. This class represents patients with the most severe and functionally limiting disease. Because of the lack of studies performed with New York Heart Association (NYHA) class IV patients, the application of aerobic exercise cannot be extended to this group of patients at this time. This review also suggests that the patient's prognosis related to heart failure may be improved after aerobic exercise because of a reduction in adverse prognostic features of the disease.10 Further trials should be performed to examine potential differences in outcomes related to training protocol and mode of training, as well as to verify results, as this study was performed more than 10 years ago.
Resistance exercise was shown to have clinical importance in improving left ventricular function, peak lactate levels, muscle strength, and muscle endurance. Three studies, all of good quality, were included.3,6,22 Two of the studies used resistance training with concentric contractions of 5 muscle groups3,6 and 1 study used maximal concentric contraction of 1 muscle group.22 The intensity and duration of resistance exercise did vary. All patients had CHF with an NYHA classes I–III CHF. The study of maximal contraction did have 1 patient with an NYHA class IV CHF.22 Bilateral resistance exercise using large muscle groups in both the upper and lower extremities of patients with NYHA classes I–III CHF is clinically recommended. There were not enough data to support the use of resistance exercise training in patients with NYHA class IV CHF. Previous studies have established that resistance exercise training in patients with NYHA classes I–III CHF is safe,3,13,15,17,18,21 and it has been shown that resistance exercise does not increase systolic BP significantly if performed appropriately.21 This review found no adverse events occurred because of resistance training in the studies analyzed. Resistance training can be used to prevent muscle atrophy associated with CHF as well as decrease the workload on active muscles during daily activities.22 Hemodynamic responses to resistance exercise in patients with CHF are similar to those in patients with CAD as well as healthy adults.13 Also, improvements on the functional 6-minute walk test in patients with CHF after resistance training were similar to those after a low-intensity aerobic protocol. Overall improvement in CHF symptoms has been shown to occur with an increase in muscle endurance after a resistance program.11 This study's findings for application of resistance training in exercise programs for patients with CHF concurs with the previous reviews and recommendations.
There is a lack of well-designed RCTs and CCTs of exercise in patients with CHF. Many recommendations have been made on the basis of literature reviews, but much of the available research is single group pretest/posttest design or case control design. Future research regarding aerobic and resistance training in patients with CHF should attempt to incorporate randomization, control groups, and blinding where possible. Studies with larger numbers of subjects will improve the generalization across various patient populations. The small number of studies meeting inclusion criteria for evaluation limits the extent to which the results of this study can be utilized as guidelines for clinical practice. Well-designed studies that examined parameters at rest and submaximal exercise were especially lacking here. Also, further research is needed to examine the relative outcomes of various parameters of exercise comparing patients with CHF to patients with other chronic diseases, especially coronary heart disease, without significant left ventricular dysfunction.
There is evidence to establish the efficacy of aerobic and resistance training for patients with CHF (NYHA classes I–III). Aerobic exercise was shown to improve v̇O2max, dyspnea, work capacity, and left ventricular function. Resistance exercise was shown to improve left ventricular function, peak lactate levels, muscle strength, and muscle endurance. The results of this study should support inclusion of aerobic exercise programs using cycle ergometry and resistance training with multiple muscle groups for patients with CHF. Also, the results provide evidence needed to educate other disciplines on the effectiveness of aerobic and resistance exercise for patients with CHF.
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