Description of the condition
Heart disease is a broad term used to describe a range of diseases that affect the heart. The various diseases that fall under the umbrella of heart disease include diseases of heart blood vessels (coronary artery disease), heart rhythm problems (arrhythmias), heart infections and congenital heart defects. Coronary heart disease (CHD) is the most common type of heart disease and its common symptoms are chest pain (angina) and heart attack (myocardial infarction). Acute coronary syndrome refers to a range of acute CHD states and includes unstable angina (chest pain at rest), non-ST segment elevation myocardial infarction (ST segment elevation generally absent), and ST segment elevation infarction (persistent ST segment elevation usually present). CHD can result in difficulties in functionality and performance of everyday activities and can impair sexual function (Racca 2010), contributing to a reduction in health-related quality of life (HRQL) (Gravely-Witte 2007).
CHD is now considered to be the leading cause of global mortality. According to the World Health Organisation, CHD accounted for 12.9% of all deaths (7 million deaths) and 5.8% of total disability-adjusted life years globally in 2011 (WHO 2014). The situation is worse in high income countries, and it has been estimated that CHD accounted for 24.8% of all deaths in Europe in 2011 (WHO 2014). However, despite the overall increase in CHD burden in high income countries, the age-adjusted death rates for this disease are declining and over half of those diagnosed now survive (Allender 2008). This is driven largely by preventive interventions, treatments to prevent death during an acute disease manifestation and rehabilitation interventions that prolong survival (Gaziano 2010). Conversely, morbidity is on the rise, with an increasing number of survivors of myocardial infarction (Mathers 2008) and an associated number of cases of chronic heart failure (HF) (Kostis 1997).
The most common cause of heart failure (HF) is CHD. Non-ischaemic causes of HF include hypertension and atrial fibrillation. HF is a complex clinical syndrome that results from any structural or functional impairment of ventricular filling or ejection of blood. It has been increasingly recognised that HF has two sub-categories: (i) impaired left ventricular contraction, which results in a reduced ejection fraction (< 35% to 50%), known as HF with reduced ejection fraction (HFREF) or ‘systolic HF’; and (ii) HF with preserved ejection fraction (HFPEF) with an ejection fraction of > 35% to 50% and also known as ‘diastolic HF'. Patients with HF experience marked reductions in their exercise capacity which has detrimental effects on their activities of daily living, HRQL, their hospital admission rate and mortality (Go 2014). In high income countries, around 2% of adults suffer from HF, but in those over the age of 65, this increases to 6% to 10% (McMurray 2005; Dickstein 2008). The prevalence and incidence of HF is steadily increasing, with approximately 825,000 new cases annually in the United Sates (Go 2014). HF has a poor prognosis, with 30% to 40% of those diagnosed dying within a year, although thereafter the mortality is less than 10% per year (Cowie 2000; Hobbs 2007). However, as with CHD, survival after HF diagnosis has also improved (Go 2014), and in the United Kingdom (UK) there is evidence of a trend of improved prognosis, with the six month mortality rate decreasing from 26% in 1995 to 14% in 2005 (Mehta 2009).
Description of the interventions
Many definitions of cardiac rehabilitation (CR) have been proposed. The following definition encompasses the key concepts of CR: “The coordinated sum of activities required to influence favourably the underlying cause of cardiovascular disease, as well as to provide the best possible physical, mental and social conditions, so that the patients may, by their own efforts, preserve or resume optimal functioning in their community and through improved health behaviour, slow or reverse progression of disease” (BACPR 2012). Whilst exercise training is a cornerstone of CR, it is recommended that 'comprehensive' programmes also include education (e.g. provision of information about a healthy lifestyle) and psychological intervention (e.g. counselling to reduce stress). CR has many of the characteristics of a 'complex intervention' as defined by in the Medical Research Council 2008 guidance for developing and evaluating complex interventions, i.e. (1) number of interacting components; (2) number and difficulty of behaviours required by those delivering or receiving the intervention; (3) number and variability of outcomes; and (4) degree of flexibility or tailoring of the intervention permitted (non-standardisation / reproducibility) (Craig 2008).
Patient education is the process by which health professionals impart information to patients that will alter their health behaviours or improve their health status (Koongstvedt 2001). There is substantial variation in the delivery of patient education for cardiac patients; it may be classroom- or home-based, group or individual, tailored or generic. Duration and reinforcement of education also differs between programmes. Some programmes are developed according to validated educational theory and by trained professionals whilst others are delivered by peers.
Interventions which specifically aim to influence psychological or psychosocial outcomes are varied and may range from organisational efforts to improve patient communication and support e.g. Jolly et al (Jolly 1998), to empirically supported psychotherapies used to target diagnosed psychopathology in cardiac patients e.g. Black et al (Black 1998). Furthermore psychological/psychosocial interventions may incorporate other elements of CR such as diet and lifestyle advice, or exercise. In some cases the intervention may be described as ‘psychological’ only to the extent that psychological techniques are used to further other treatment goals.
The patient groups routinely recommended for CR include those with post-myocardial infarction, post revascularisation procedure, and HF. Traditionally, CR programmes have been offered in a supervised centre-based setting. However, many patients fail to receive rehabilitation (Bethell 2008) and current uptake of CR for both CHD and HF appears to be sub-optimal (Tierney 2011; Dalal 2012; NICE 2013). Home-based CR programmes have been increasingly introduced to widen access and participation. In addition to uptake, maintaining longer term adherence to CR is also a key challenge (Daly 2002; Moore 2003) and therefore interventions aimed at improving patient uptake and adherence to CR programmes have been adopted and will also be investigated in this overview.
Based on current evidence, national and international guidelines on the management of CHD and HF including those by the American College of Cardiology/American Heart, European Society of Cardiology and National Institute for Health and Care Excellence (NICE) in the UK, consistently recommend CR as an effective and safe intervention (NICE 2010; McMurray 2012; NICE 2013; Yancy 2013).
How the intervention might work
The mechanism by which CR might work depends on the patient group and the component of rehabilitation being considered. The majority of mechanistic evidence is for exercise training.
For those with CHD, exercise training has been shown to have direct benefits on the heart and coronary vasculature, including myocardial oxygen demand, endothelial function, autonomic tone, coagulation and clotting factors, inflammatory markers, and the development of coronary collateral vessels (Clausen 1976; Hambrecht 2000). However, findings of the original Cochrane review of exercise based CR for CHD (Jolliffe 2001) supported the hypothesis that reductions in mortality may also be mediated via the indirect effects of exercise through improvements in the risk factors for atherosclerotic disease (i.e. lipids, smoking and blood pressure) (Taylor 2006).
The precise mechanism(s) through which exercise training benefits patients with HF remains unclear. One explanation, applicable to patients with ischaemic causes of HF, is that exercise training improves myocardial perfusion by alleviating endothelial dysfunction therefore dilating coronary vessels and by stimulating new vessel formation by way of intermittent ischaemia (Piepoli 2004). Indeed, Belardinelli and colleagues have demonstrated that aerobic training improves myocardial contractility and diastolic filling (Belardinelli 1998). A meta-analysis by Haykowsky et al demonstrated the benefits of exercise training on cardiac remodelling as measured by ejection fraction, end-diastolic volume, and end-systolic volume (Haykowsky 2007). Regardless of cause, there are important neurohormonal and musculoskeletal abnormalities in HF. Exercise training may reduce adrenergic tone and increase vagal tone, as suggested by an assessment of variability in heart rate. Skeletal muscle dysfunction and wasting may also respond to exercise training (Piepoli 2004). Hambrecht et al have demonstrated that regular physical activity in HF patients stimulates vasodilatation in the skeletal muscle vasculature (Hambrecht 1998).
The benefits of education and psychological interventions depend on patient behaviour change including improvements in healthy lifestyle and changes in mood, such as reductions in depression and anxiety.
Why it is important to do this overview
In 2001, Jolliffe et al published the first Cochrane review of CR, summarising the evidence of 32 randomised controlled trials (RCTs) in 8440 post-myocardial infarction and revascularisation patients, and confirming a mortality benefit of exercise-based CR (Jolliffe 2001). With the funding support of the National Institute of Health Research (NIHR) in United Kingdom, over the last 10 years the portfolio of published Cochrane reviews has grown to six systematic reviews/meta-analyses:
Exercise based rehabilitation for heart failure (Taylor 2014a);
Home-based versus centre-based cardiac rehabilitation (Taylor 2014b);
Exercise-based cardiac rehabilitation for coronary heart disease (Heran 2011);
Psychological interventions for coronary heart disease (Whalley 2011);
Patient education in the management of coronary heart disease (Brown 2011);
Promoting patient uptake and adherence in cardiac rehabilitation (Karmali 2014).
The development of the portfolio of Cochrane reviews has reflected many of the key areas of evolution in the provision of CR and how this model of service delivery can differ across international healthcare jurisdictions i.e. the shift from emphasis on exercise therapy alone to comprehensive secondary prevention including risk factor and dietary education and management of psychological factors; the expansion of the population of cardiac patients receiving CR services to include heart failure; the development of alternative settings of CR delivery that include home provision in addition to the traditional supervised hospital- or centre-based programmes; and the need to broaden the consideration of the outcomes of CR to inform the needs of healthcare policy makers (e.g. impacts on hospital admission, HRQL, and healthcare costs). This Cochrane CR review portfolio remains dynamic, with 3 reviews having undergone an update in the last 12 months (Karmali 2014; Taylor 2014a; Taylor 2014b).
The portfolio of Cochrane reviews has played an important role in informing evidence-based policy for CR nationally and internationally, and the reviews have been cited in a number of key clinical guidelines including those by the American College of Cardiology/American Heart, European Society of Cardiology and NICE in the UK, that consistently recommend CR as a safe and effective intervention (NICE 2010; McMurray 2012; NICE 2013; Yancy 2013).
Overviews of systematic reviews (overviews) are a new approach to summarising evidence, synthesising results from multiple systematic reviews into a single usable document (Becker 2011). By providing a single synthesis of all relevant evidence in a particular area, overviews may be useful for therapeutic and policy decision-making, providing a comprehensive ‘friendly front end’ to the evidence, so that the reader does not have to assimilate the data from separate systematic reviews. Overviews can also help inform the strategic direction of conduct and structuring of future systematic reviews. For example, the latest version of the Cochrane review of exercise based CR for CHD includes 47 RCTs in over 10,000 patients and may therefore benefit from being organised into sub-reviews ('splitting') according to CHD indications i.e. post-myocardial infarction, revascularisation and angina. Finally, overviews provide an opportunity to identify potential 'evidence gaps' and therefore inform areas in which new Cochrane reviews should be prioritised.