Abstract

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Introduction: Heart failure (HF) is a complex clinical syndrome that is growing as a public health problem with over 1 in 7 of those over the age of 85 affected. Despite improvements in prognosis, the mortality rate remains high. Exercise training (ET) has been reported to be beneficial in patients with heart failure as it improves exercise tolerance and quality of life. The aim of this study is to see if ET is safe and if it significantly improves exercise tolerance, mortality and quality of life (QoL) in patients with heart failure.
Methods: Online databases such as Medline (Ovid), PubMed and NHS Evidence were searched for any available literature on exercise training in heart failure patients. Four recent articles were chosen to be critically appraised in order to address the aim.
Results: All four articles found exercise training to be safe and of some benefit for HF patients. Two studies found peak oxygen uptake (VO2 max) and 6-minute walking test (6MWT) to significantly improve with exercise. An additional study found a non-significant rise. Three of the studies found exercise to significant improve QoL.
ET is beneficial for patients with HF as it is safe and would improve QoL. It may also improve their VO2 max and 6MWT to some extent.
Conclusion: Exercise training may be beneficial to people with heart failure. Motivation and targets with careful intervention from community nurses may help to sustain this regimen.

Introduction

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Heart failure (HF) is a complex clinical syndrome that can result from any structural or functional cardiac disorder (1). It results in the heart failing to meet the body’s physiological demands. There are two main types of classification of heart failure: heart failure with preserved ejection fraction (HFPEF) and Left ventricular systolic dysfunction (LVSD) (18). Heart failure is further classified into new onset, transient or chronic depending on the rate of onset and duration of symptoms (2).
HF is a major public health problem with almost 1 million people affected in the UK (3). The incidence of heart failure rises with age with almost 1 in 7 of those aged over 85 suffering from the condition (4). Even though the prognosis of HF has improved over the years, the mortality rate still remains high with only 50% of patients alive after 5 years and 30-40% dying within 1 year of being diagnosed (5,6).
HF accounts for approximately 5% of hospital admissions and costs the NHS over £1 billion per year (1). Over the next 25 years, HF admissions rates are expected to increase by 50% (7).
Coronary Heart Disease is the most common cause of HF accounting for almost 70% of cases with many of these previously having suffered a myocardial infarction . Other causes include hypertension, atrial fibrillation and cardiomyopaties (1). Causes of both left and right heart failure are shown in table 1. As a result of haemodynamic changes found in HF, significant changes occur to both the heart and peripheral vascular system.
Risk factors that increase the likelihood of HF include smoking, alcohol, diabetes mellitus, obesity and family history (9). Men are at greater risk of HF with the incidence being up to 60 percent higher compared with women (10).
Clinical features of heart failure depend upon the cause and type of heart failure. In left HF, patients commonly experience fatigue, wheeze, breathlessness (exertional dyspnoea, orthopnoea and paroxysmal nocturnal dyspnoea) and exercise intolerance (11). Orthopnoea occurs at rest with the patient lying down and paroxysmal nocturnal dyspnoea (PND) occurs when the patient is sleeping (12).
Pulmonary and systemic congestion leads to signs such as ankle swelling, additional heart sounds, raised jugular venous pressure, ascities, hepatomegaly and bi-basal crackles (12).
The severity of HF symptoms are graded into one of four functional classes by the New York Classification of HF. This classification is useful in the preoperative assessment and management of patients (12).
Diagnosis of HF is based on clinical findings in conjunction with investigations. The National Institute of Clinical Excellence (NICE) recently recommended that patients with no previous history of myocardial infarction suspected of HF should have levels of serum B-type natriuretic peptide (BNP) measured, a hormone secreted in response to myocyte stretch from the ventricular myocardium (7). Echocardiography is recommended for patients with a previous history of MI and would diagnose and determine the cause of HF (7).
Other investigations that may aid diagnosis and find the cause of HF include full blood count, chest x-ray and electrocardiogram. Peak oxygen consumption (VO2 max) carried out during cardiopulmonary exercise testing is a reliable indicator in the prognosis of HF (13).
Treatment of HF aims to increase the patient’s quality of life (QoL) by relieving symptoms and improving the prognosis. Before any pharmacological intervention is initiated, patients are educated and advised on lifestyle modifications such as smoking, alcohol, diet and exercise (7).
Pharmacological treatment involves a variety of medications and the drug selected should involve careful consideration of the patient’s condition and the latest published guidelines. Patients with LVSD are commenced on angiotensin-converting-enzyme inhibitors or beta-blockers depending upon the doctors clinical judgement and side effect profile of the patient (7). Any underlying causes of HF should also be treated. Surgery may be used as a last resort in young patients with severe HF or in those who fail to respond to intensive medical treatment as transplantation offers a significant improvement in QoL with 75% success rate after 5 years (1).
There are several complications that can result from HF. Arrythmias can occur at any time in those with HF with the prevalence rising with worsening of heart failure (14). Up to one third of patients develop severe depression (15). Sexual dysfunction is common and may occur due to medications such as beta-blockers, depression or fatigue (2). The most serious complication occurring in severe heart failure is cachexia. Those with cachexia have a poor prognosis and a shorter life expectancy than most of those with cancer (2).
Exercise has been proven to have many health benefits by reducing the mortality and morbity of many conditions such as stroke, coronary heart disease, dementia, diabetes and certain types of cancer (16). Furthermore, exercise improves general well being by improving sleep, general fitness and reducing stress (17,18).  Its beneficial effects in HF are due to positive effects on skeletal muscle, autonomic function, endothelial function, neurohormonal function and insulin sensitivity (19). In addition, exercise therapy (ET) may improve the QoL of HF patients by improving exercise tolerance (20).
The six-minute walk test (6MWT) has been proven to be a simple and reliable test in order to objectively evaluate functional capacity in HF as it measures the distance walked in 6 minutes (21,22). VO2max also allows objective assessment of exercise capacity, however, it is time consuming and costly (23). Both the 6MWT and VO2max can be reliably used as an objective endpoint in measuring the effectiveness of exercise therapy in HF.
The aim of this review is to investigate whether exercise prescription in HF is safe and if it significantly improves exercise tolerance, QoL and mortality.

Methods and Results

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Background reading was conducted on the topic of HF and exercise prescription by obtaining books from the University of Liverpool library.
The World Health Organisation (24), British Heart Foundation, NHS websites were accessed for general information on HF. For the latest guidelines on heart failure, the NICE and the European Society of Cardiology websites were accessed.
In order to attain articles to critically analyse, a variety of online databases were used. These included Medline (via Ovid), Scopus, PubMed and NHS evidence.
Medical subject heading (MeSH) terms including heart failure, exercise and exercise therapy were applied to searches. To reduce the number of results to relevant articles only, these were then limited to availability in English, human species, randomised controlled trials (RCT) and published in the last five years. Finally any articles that appeared irrelevant were disregarded.
After applying the inclusion and exclusion criteria, the four most relevant and recent articles were selected to review (table 2).
The four chosen articles were critically appraised using criteria adapted from the NHS Public Health Resource Unit tools (25).
The results are summarised in table 3-4.

Discussion

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Study 1 (27)
Yeh et al conducted a single-blind rct on 100 patients with class I-III HF. In the ET group, 50 patients underwent 12 weeks of twice weekly tai chi. They concluded that tai chi was safe and beneficial to HF patients as it improved QoL and mood. However, they also found that compared to the control group there was no significant difference in VO2max and the 6MWT.
This study was not free from selection bias as only patients from clinics such as specialist HF and cardiology were recruited. Furthermore, this could question the validity of the conclusion when applied to the wider population. The study recognizes that it failed to identify a definitive physiological mechanism for the beneficial effects seen of tai chi but does try to justify this by saying that this study was the first large scale tai chi RCT conducted on HF patients.
The study justifies its sample size and tried to eliminate confounding factors by stratifying participants into both groups and which strengthens the validity of the results.
Although the study had good rates of adherence with 75% of classes attended in the tai chi group and 66% in the educational group, there were some dropouts outs which were in the form of deaths and hospitalisation.  This may lead to attrition bias, however, the study carried out all statistical analysis on an intention to treat basis.
As this was only single blinded, there is a chance that performance bias may have affected the results. Patients in the tai chi group may have experienced a placebo effect and this could be evident in the outcomes. There was no significant difference in the objective outcomes such as the VO2max, 6MWT and BNP but there was a difference in the subjective outcomes such as the QoL questionnaire and mood state questionnaire.
Although patients in the control group were asked not to start tai chi during the study period, it is not known if these patients did any other forms of exercise. This could have introduced a confounding factor that may have affected the results.
The study mentions that each session was taught by one or two tai chi instructors out of a total of six. As the instructor changed regularly with some sessions having an additional instructor, the enthusiasm and motivation given to the participants would have varied thus creating a confounding factor. Thus a consistent instructor or central person such as a nurse may counter these effects.
When measuring exercise capacity, participants were encouraged to exercise until exhaustion with the amount of exertion perceived by participants measured by the Borg RPE scale. As this scale is subjective, it relies on participants to be truthful and accurate when rating their perceived difficulty of the exercise undertaken. As the measurement may not always be consistent, it shows a limitation of the Borg scale and therefore highlights a potential weakness in the results of the study.

Study 2 (28)
This single-blind RCT found that 16 weeks of ET was safe and significantly improved VO2max, 6MWT, peak power output and physical QoL in older participants. Out of 24 ET participants who completed the follow up, 19 (79%) had an improvement in their VO2max compared to 11 (50%) in the control group. An improvement of more than 10% in VO2max is clinically significant and this was surpassed by more than 67% of participants in the ET group and 27% in the control group. However, there were no differences reported in the doppler ultrasound, BNP and norepinephrine.
The study population in both groups consisted mostly of female patients and therefore this could question the validity of the results as they cannot confidently be applied to the male population who are at greater risk of HF.
Compliance to the exercise training regime was very good with participants averaging 88% attendance during the 48 sessions with 98% attending more than 2 sessions per week. However, the study excluded patients who had any history of non-compliance. The study was therefore prone to selection bias as the study population would not be representative of the general population who would have a certain degree of non-compliance.          
The study itself acknowledges that because they only recruited stable patients who were ambulatory, they cannot apply their results to patients who are sicker, less stable and immobile.
Although the study found supervised exercise therapy safe and effective in heart failure it acknowledged that their results do not address whether unsupervised or home based exercise therapy would be safe and effective. This would be an area of interest especially with nurse led exercise regimes.
The study recognised that its sample size may be modest but justified it with a power analysis. Fifty three patients were recruited from reviewing hospital records and this could allow selection bias as they were not recruited randomly.
The study also accepted that it could not be certain if the control participants undertook any exercise secretly and omitted it on questioning. However this is a general limitation of any RCT undertaken on exercise training and could have equally affected all four articles.

Study 3 (29)
This was the largest multicentre RCT conducted on exercise training in HF with 2331 participants. They found that ET resulted in modest significant reductions in all-cause mortality or hospitalisation in patients who have stable HF after adjusting for highly prognostic predictors of the primary end point. There was a greater improvement in VO2max in the ET than in the control group, however, this was only 4% which is not clinically significant as it was less than 10%.
Allocation bias in this study was eliminated as patients in this study were randomised using a permuted block randomisation scheme. Furthermore, the study strengthened the validity of its results as it eliminated any potential confounding factors by stratifying patients in terms of clinical centre and aetiology of HF. The inclusion and exclusion criteria of this study were similar to the other studies.
After 36 supervised exercise sessions, patients were fully undergoing home based exercise. The authors defended their method stating that conducting a completely supervised exercise study was not feasible and is unlikely to be implemented into practice. The expectations of the home-based training regime were high as participants were required to cycle or use the treadmill 40 minutes a day, five times a week. Adherence throughout the study was measured by attendance logs for the initial supervised training period and then activity logs and telephone follow up. Considering the high expectations of the home based training regime, patients could have lied or exaggerated about their home based activity. However the researchers addressed this issue by monitoring data from the participant’s heart rate monitors.
The study also justified its sample size with a calculation and had a 90% power to detect a statistical difference. Adherence to exercise training was variable with only 30% of patients meeting or exceeded the target set for exercise minutes per week at any point during the trial.
The authors reported that based on self-reports by participants in the control group and telephone follow-ups by study personnel, approximately 25% of patients exercised in every 3 month windows for the first 2 years and 8% exercised throughout the length of the trial. However, the average weekly time spent exercising by those in the control group was approximately half of that in the exercise training group. This could question the validity of the study as the variable under study, exercise, was not completely absent in the control group. Interestingly in this study 55% of patients in the control group were unhappy that about their group assignment compared to 2% in the exercise training group.
ET was generally safe as only 37 patients out of 1159 (3%) in the exercise group required hospitalisation within 3 hours of exercise. Furthermore only 5 patients (0.4%) died within 3 hours of exercise in both groups. However, 5 patients also died in the control group within 3 hours of exercising. Ideally to make a fair comparison regarding exercise in HF, only those in the intervention group would exercise. Restricting exercise for only the patients in the control group is unethical considering that exercise has been proven to be beneficial for patients with HF (26,27).

Study 4 (30)
Karapolat et al conducted an 8 week randomised study comparing hospital and home-based exercise on patients with HF and found that exercise in both groups significantly improved VO2max, 6MWT, left ventricular systolic function and QoL. Furthermore they also found that exercise reduced depressive symptoms in both groups.
Like previous studies, this study was not free from selection bias as only patients from a cardiac rehabilitation centre were recruited. As only modest numbers of patients were participating in the trial, the external validity of the conclusion to the wider HF population could be limited. Furthermore the mean age of participants in the hospital-based and home-based exercise groups was 45 years and 44 years respectively. Selecting patients who were older would have increased the generalisability of the conclusion to the wider population as the incidence of HF rises with age. Furthermore these patients would have less co-morbidities due to their younger age and would find exercise more easier to undertake.
The study eliminated observer bias by using the same person to carry out all exercise testing. By consistently using the same person to carry out all exercise testing, the study increased the reliability of the results. Furthermore the study tried to eliminate observer bias and increase the reliability of the results by using the same echocardiographic specialist who was blinded to the group allocation of the participants.
The 6MWT was conducted 4 hours before the cardiopulmonary testing which ensured that patients had plenty of time to recover which would have otherwise affected the results of the latter test. A heart rate monitor and pedometer given to those in the home based group measured the intensity of the exercise and distance walked.
Randomisation was done using concealed envelopes and participants in both groups were similar at baseline. However the study fails to mention if participants were stratified as this would have eliminated any confounding factors that may have affected the results.
Unlike the other articles, this study clearly mentioned that they had approval from a local ethics committee.
The trial had no adverse events during exercise in both groups which shows that exercise was safe. However, this may not have been the case had the sample size been larger. The study recognised that some of its limitations were that the absence of a control group and the short 8 week trial could not assess the long term effects of exercise on HF.
There have been limited information regarding the role of health care professionals such as nurses to lead these interventions and is an area that should be looked at in more detail.
A nurse in the community may know patients better and provide a continuity of care with tailored exercise programs varying from week to week depending on the clinical impression of the nurse.
Out of the four studies only one study compared home-based exercise with hospital-based exercise and found them both to be equally effective at improving functional capacity and QoL. The other three studies compared an ET group with a control group. Study 1 found ET to improve QoL and mood. However, it did not find a significant difference in VO2max and the 6MWT between the two groups. In contrast study 2 did find that exercise training significantly improved VO2max and 6MWT as well as QoL when compared to the control group. Study 3 was the most robust RCT conducted and found that ET only resulted in modest significant reductions in all-cause mortality or hospitalisation. They did find a small improvement in VO2max in the ET group, though it was not clinically significant enough.
In conclusion, ET is beneficial for patients with HF as it is safe and would improve QoL. It may also improve their VO2max and 6MWT to some extent.

Conclusion

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Exercise training may be beneficial to people with heart failure. Motivation and targets with careful intervention from community nurses may help to sustain this regimen as well as tailor it to individual needs especially amongst the elderly.

References

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Source(s) of Funding

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Competing Interests

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