INTRODUCTION

Cardiac rehabilitation is an accepted form of management for people with cardiac disease. Initially rehabilitation was offered mainly to people recovering from a myocardial infarction (MI), but now encompasses a wide range of cardiac problems. More than 275 000 people have a MI each year in England and, while more than 40% of these are fatal, the survival rate is improving (Department of Health 2006). With more people surviving the peri-infarct period, the incidence of people with chronic heart failure (CHF) is increasing. These changes in mortality and morbidity present challenges for health professionals involved in organizing and delivering rehabilitation programmes. The aim of cardiac rehabilitation is to enable people to regain full physical, psychological and social status and, in order to optimize long-term prognosis, to promote and implement coronary heart disease (CHD) secondary prevention measures. Cardiac rehabilitation should be an integral part of both acute care and long-term follow-up, but provision and uptake remains inconsistent (Beswick et al 2004, Bittner & Sanderson 2006, Brodie et al 2006). In the United Kingdom (UK), the National Service Framework for CHD (Department of Health 2000) was written to provide guidance on the management of people with coronary heart disease. One of the standards of recommended care is the provision of a multidisciplinary programme of cardiac rehabilitation and secondary prevention. There is large variation in the format and organization of rehabilitation programmes, both within and between countries, but traditionally most encompass a period of exercise training, education sessions, psychosocial support and advice/counselling for both the patient and their family. In addition to people with a MI or CHF, participants may include those with an implanted cardioverter defibrillator (ICD), pacemaker and following coronary artery bypass graft surgery (CABG) and transplantation. Demographic changes mean there is greater involvement of elderly people, which is both a reflection of an ageing population and expansion of health care, and there is also a gradual increase in the uptake of cardiac rehabilitation amongst women. The secondary prevention aspect of the programmes has an important place in the reduction of risk factors. Physically inactive people have approximately double the risk of CHD compared with active people and the implementation of regular exercise is considered to decrease their risk factor profile by the same magnitude as smoking cessation (Albu et al 2006, Department of Health 2004).

This chapter describes the exercise component of cardiac rehabilitation which is the aspect in which physiotherapists are mainly involved and is divided into five parts:

evidence base for comprehensive rehabilitation

provision of cardiac rehabilitation

benefits of exercise training

exercise prescription

programme implementation.

EVIDENCE BASE FOR CARDIAC REHABILITATION

With the increased evidence base for the benefits of cardiac rehabilitation, and particularly exercise training, many clinical guidelines for the management of people with cardiac problems recommend participation in a rehabilitation programme (National Institute for Clinical Excellence 2001, 2003, Scottish Intercollegiate Guidelines Network 2002). While there is a plethora of research supporting the benefits of cardiac rehabilitation programmes, the era in which the information was obtained has to be taken into consideration. Early studies concentrated on the benefits of exercise for post-MI patients in whom traditional management had restricted early activity – which differs from the early resumption of activity practised today. Early studies did not include the benefits of revascularization, thrombolysis and protective drug therapy (Franklin 2004, Kovoor et al 2006, Zwisler et al 2005). The restriction of studies to exercise training also limits their applicability to comprehensive cardiac rehabilitation programmes, as the sum of a programme may be greater than its individual parts. Additionally, women and the elderly were often excluded from research (Witt et al 2004). Consequently, most of the research findings in the 1960s and 1970s are no longer directly applicable to the management of people following a MI. The meta-analyses of Oldridge et al (1988) and O’Connor et al (1989) which have been used extensively to promote cardiac rehabilitation are now of limited usefulness and have been superseded by more recent studies (Jolliffe et al 2000, Rees et al 2004, Taylor et al 2004).

Current research continues to suggest that rehabilitation programmes confer benefit to participants in all domains of their lives, with a focus on patient selection and organization of the programme. Unfortunately the methodology of some research studies is of low quality (i.e. small sample number, restricted age/gender, lack of randomization), which limits extrapolation of their findings to clinical practice. Another problematic area for interpreting research findings is the choice of outcome measures (Sanderson et al 2004). The importance of improvement in health-related quality of life is recognized in many studies, but there is lack of consensus as to the most appropriate measuring tool (Shephard & Franklin 2001, Taylor et al 1998). The SF-36 and SF-12 Health Status Questionnaires have been widely used, but concern has been expressed as to their ability to detect change when used for serial measurements (Ni et al 2000, Smith et al 2000). Some studies suggest anxiety and depression improve after a period of rehabilitation and have been commonly measured by the Hospital and Depression Scale (Zigmond & Snaith 1983), but this is thought to be relatively insensitive to change in this group of patients (McGee et al 1999). With the difficulties in selecting robust and appropriate outcome measures for quality of life issues, studies frequently use physiological or exercise endurance indices to measure responses to exercise training. However, these also have methodological issues concerning the influence of motivation and relevance of results (Ingle et al 2005). It has been suggested that a suitable measure for people with ICDs is the confidence to exert themselves physically (Sears et al 2004). Measurements of general activity, using pedometers, are considered to demonstrate a close relationship with changes in functional status (Evangelista et al 2005) and may be a more appropriate outcome for determining the response to rehabilitation programmes.

The organization of cardiac rehabilitation programmes is varied, with some focusing primarily on education and psychosocial intervention (Mendes de Leon et al 2006) and others offering only exercise training. The World Health Organization (WHO) (Frye 1993) definition of cardiac rehabilitation encompasses the concept of comprehensive cardiac rehabilitation programmes. Research suggests the inclusion of exercise training is a key element in eliciting benefits both in facilitating return to function and secondary prevention (Leon et al 1991, National Institute for Clinical Excellence 2003, Taylor et al 2004). There is considerable variation across and between patient groups in the type and setting of exercise training (Hansen et al 2005). Many studies have concentrated on aerobic exercise owing to concerns regarding the effects of resistance training on cardiac function, but there is growing evidence that a mix of endurance and strength exercises are both safe and optimize the benefits (Adams et al 2006, Delagardelle et al 2002, Jonsdottir et al 2005, Levinger et al 2005). Concern that some patients may develop myocardial remodelling, as a result of participating in early activity (Jugdutt et al 1988, Kloner & Kloner 1983), has been alleviated by other work indicating that exercise does not contribute to the onset of remodelling (Cannistra et al 1999, DuBach et al 1997, Giannuzzi et al 1993, Myers et al 2000). The benefits of low- intensity exercise in the early stages of a programme are thought be similar to those of higher intensity (Blumenthal et al 1988, Goble et al 1991, Worcester et al 1993) and adoption of low-intensity exercise would facilitate both adherence and safety. Women have previously been under-represented in cardiac rehabilitation and may require specific programmes, based in the community or at home, to improve their uptake and adherence (Sanderson & Bittner 2005, Todaro et al 2004, Witt et al 2004). Some studies recommend inspiratory muscle training in people with chronic heart failure (Dall’Ago et al 2006).

The duration of the period of exercise training is influenced by many factors, such as physiological and psychological state (Kovoor et al 2006), objectives and adherence. Secondary prevention requires a prolonged period of training (Brubaker et al 2000) and adherence and uptake to a programme may be influenced by social support (Husak et al 2004) age, gender (Todaro et al 2004) and location of training (Grace et al 2005). The lack of consensus on an optimal period of exercise training for different groups of patients and an absence of a robust prediction model to determine the magnitude of benefit each patient may receive from a rehabilitation programme (Pierson et al 2004, Shen et al 2006) places an emphasis on assessment, joint goal setting and regular re-evaluation of response. Few studies have included a prolonged follow-up period, but any benefits appear to be quickly lost on cessation of regular exercise training.

The diversity of programmes and client groups makes it difficult to determine the cost-effectiveness of cardiac rehabilitation and this is compounded by differences in health provision among countries where this has been investigated. A survey within the UK calculated the cost per patient to be of the order of £490 (Beswick et al 2004) while an American review had higher average costs of $2054 and determined that participation prolonged survival by an additional 1.82 years at a cost of $1773 per/life-year saved (Georgiou et al 2001). It has been suggested that cardiac rehabilitation is more cost-effective than thrombolytic therapy and coronary bypass surgery (Ades et al 1997).

There has not been any reported increase in adverse events during either supervised or unsupervised exercise training following the inclusion of people who were previously considered a high risk: i.e. CHF and ICDs (Davids et al 2005, Fitchet et al 2003, Pashkow et al 1997) However, there is a paucity of information on the occurrence of adverse events outside research studies, which usually include highly selected patients who undergo formal exercise tests.

PROVISION OF CARDIAC REHABILITATION

Goals

Cardiac rehabilitation should meet the emotional, educational and physical needs of cardiac patients and their families in the acute hospital phase, through outpatient care and long-term follow-up in the community. It should be an integral part of cardiological management, with common goals to:

decrease cardiac morbidity and relieve symptoms

promote risk modification and secondary prevention

decrease anxiety and increase knowledge and self-confidence

increase fitness and the ability to resume normal activities.

Cardiological management involves assessment, risk stratification (the ‘risk’ of further cardiac events), diagnostic testing, drug therapy and revascularization interventions, e.g. percutaneous coronary intervention (PCI) and CABG. There should be close collaboration between cardiology and rehabilitation professionals on risk stratification, levels of prescribed exercise and discussion of treatment plans for symptomatic patients.

Rehabilitation should combine exercise with patient education and counselling, which provide:

reassurance, support and information

risk factor modification and an appropriate behavioural change programme

assessment and risk stratification

exercise prescription and an activity programme.

Patients should be offered an individually tailored package from this menu of care, according to their needs and preferences (Scottish Intercollegiate Guidelines Network 2002). Individual packages are usually described as spanning four phases of care (Coats et al 1995):

Phase I in-hospital period (average 3–5 days)

Phase II immediate post-discharge/convalescence stage (2–6 weeks)

Phase III supervised outpatient programme (6–12 weeks)

Phase IV long-term maintenance programme in the community.

However, there is now less emphasis on a fixed time scale; patients are increasingly offered a more seamless transition of care between outpatient follow-up and long-term lifestyle maintenance in the community.

Considerable variation exists in the model, timing, content and delivery of outpatient cardiac rehabilitation. Rehabilitation may be offered in supervised groups, within a hospital or community setting, or as part of a home-based package. Some programmes include education, psychosocial and exercise components while others provide only exercise training; some programmes are confined to 4–6 weeks’ duration while others last for up to a year. In order to maximize benefit and adherence, the rehabilitation professional must match the appropriate model of care to each patient’s individual needs. Increasing use of national clinical guidelines and audit tools have led to increased standardization, quality and effectiveness of cardiac rehabilitation services (American Association of Cardiovascular and Pulmonary Rehabilitation 2004, American College of Sports Medicine 2006, Fletcher et al 2001, Leon et al 2005, Scottish Intercollegiate Guidelines Network 2002).

BENEFITS OF EXERCISE TRAINING

Improved exercise capacity

The development of cardiovascular endurance is the primary objective for CHD patients. Endurance training, defined as any activity which uses large muscle groups, can be sustained for a prolonged period and is rhythmic and aerobic in nature, results in an increase in maximal oxygen uptake (VO₂max), i.e. the highest rate of oxygen consumption attainable during maximal exercise. Maximal oxygen uptake is limited:

centrally by cardiac output (CO), which is a function of heart rate (HR) and stroke volume (SV)

peripherally, in particular by the capacity of skeletal muscle to extract oxygen from the blood. This is represented as the difference between the oxygen content of arterial blood and mixed venous blood (arteriovenous oxygen difference Consequently an increase in O₂max depends on the potential for inducing central and/or peripheral adaptations.

Central changes

In healthy individuals, endurance training results in a significant increase in maximal cardiac output. Maximum heart rate does not alter with training and so the increase in CO must arise from a training-induced increase in maximal SV. This is achieved primarily through:

increased left ventricular mass and chamber size

increased total blood volume

reduced total peripheral resistance at maximal exercise.

Peripheral changes

Training-induced changes within skeletal muscle, which contribute to increased extraction and utilization of oxygen, include:

increased number and size of mitochondria

increased oxidative enzyme activity

increased capillarization

increased myoglobin.

In cardiac patients, the increase in VO₂max is attributed predominantly to peripheral adaptation. Central changes are associated with prolonged periods of high-intensity training and although in selected patients central changes have been provoked (Ehsani et al 1986, Schuler et al 1992), the high intensity of the training regimen would be inappropriate for the heterogene- ous group of patients eligible for cardiac rehabilitation programmes.

Consequences of an increase in maximal oxygen uptake

The significance of an increase in VO₂max for cardiac patients is not that it permits a higher level of maximal effort (as this is rarely demanded in everyday life) but that repeated submaximal activities of daily living constitute a smaller percentage of the increased maximal capacity and therefore impose relatively less physiological stress. This is reflected in a reduction in heart rate (attributed to both increased vagal tone and reduced sympathetic outflow), blood pressure and plasma catecholamine concentrations at rest and at submaximal workloads. Since myocardial oxygen consumption (MVO₂) is determined by heart rate and systolic blood pressure (referred to as rate pressure product (RPP) or double product), a reduction in either or both delays the onset of ischaemia and lessens the potential for arrhythmias. A further benefit of the training-induced bradycardia is that, at any reference submaximal workload, the period of diastole is extended and, since 80% of coronary blood flow occurs during the relaxation phase of the cardiac cycle, myocardial perfusion is significantly enhanced.

Risk factor modification

In cardiac patients exercise may have an important secondary prevention role. The rationale for aggressive risk factor modification, as part of optimal care of coronary heart disease patients, is based on the premise that the factors that contribute to initial development of disease will also influence the progression of established disease and the likelihood of future events. The ‘acute’ effects of each bout of exercise in healthy people include:

a raised post-exercise metabolic rate

changes in lipoprotein metabolism with consequent increased synthesis of high-density lipoprotein (HDL)

improved insulin sensitivity

decreased blood pressure.

These effects all relate to local changes in the previously exercised muscle and are evident even after light to moderate exercise, suggesting that a general increase in physical activity is likely to contribute to the patient’s continued well-being and to the reduced mortality and morbidity associated with exercise rehabilitation.

In addition, exercise training is known to reduce known triggers for cardiac events including:

preventing thrombus formation

improving endothelial function

reducing potential for serious arrhythmias.

EXERCISE PRESCRIPTION

Principles of exercise prescription

When individual bouts of exercise are repeated regularly, and in accordance with established principles of training, a series of longer-term cardiovascular and metabolic adaptations occur; for instance, as described earlier, an increase in VO₂max results from aerobic endurance training.

The principles of exercise training are:

Individuality – heredity plays a major part in how quickly and to what extent an individual’s body adapts to a training programme: i.e. no two individuals (other than identical twins) will exhibit the same adaptations in response to the same training programme.

Progressive overload – overload refers to placing greater demands on the body than it is accustomed to, thereby provoking adaptations. In order to continue to stimulate training adaptations, the overload must be progressively increased.

Regression or reversibility – this principle is often referred to as the principle of ‘use it or lose it’: i.e. if the stimulus to change (the overload) is withdrawn, the adaptations conferred will diminish until the level of functional capacity is once again sufficient to meet only the demands imposed by general activities of daily life.

Specificity – the adaptations conferred by training are highly specific to:

the volume of training, which includes the Frequency and duration (or Time) of training

the Intensity of training

the mode or Type of training

The effectiveness and appropriateness of all exercise prescriptions will depend upon manipulation of the FITT principle: i.e. the frequency, intensity, time and type of training.

Intensity of exercise

The intensity of exercise is a critical issue because vigorous activity carries a greatly increased risk of precipitating adverse events such as myocardial infarction or arrhythmias (Willich et al 1993). Frequent, moderate-intensity exercise is recommended for CHD patients since it will optimize benefits without increasing the risk of adverse events (Dafoe & Huston 1997). For individuals with greatly diminished functional capacity, several short bouts (as little as 5–10 minutes) throughout the day may be advisable. There are a number of established methods for prescribing and monitoring intensity, which may be used separately or in combination with one another.

Use of heart rate

Ideally, training heart rate is based on information derived from a maximal or symptom-limited exercise electrocardiogram test (ETT) (Box 14.1). Where a maximal test has been achieved, training heart rate should be set at 60–75% of maximal heart rate (HRmax). If the test was symptom limited, training intensity should be set at 10–20 beats per minute (bpm) below the heart rate at which symptoms were apparent and the patient’s heart rate should be monitored throughout each exercise session. ECG test information is, however, not always available to health professionals. In the absence of test data or if, for diagnostic purposes, a patient performs the exercise test ‘off-medication’, other methods for establishing appropriate training intensity have to be used.

Box 14.1 Exercise tolerance testing

In the cardiology setting, an exercise ECG using an incremental protocol is the most common method for determining cardiac perfusion and function. Its major applications are:

diagnosis – to identify patients with CHD and the severity of their disease

prognosis – to identify high-, moderate- and low-risk patients

evaluation – to establish the effectiveness of a selected intervention

measurement of functional capacity – on which advice about activities of daily living and a formal exercise prescription may be based

measurement of acute exercise responses including blood pressure, heart rate, ventilatory responses and detection of exercise-induced arrhythmias.

Numerous exercise protocols have been developed which utilize a variety of different exercise modes, but in the United Kingdom an incremental treadmill protocol is the traditional test mode. Before acceptance into a Phase III programme, usually 2–6 weeks post MI, a symptom-limited test (i.e. the patient continues until signs or symptoms, which necessitate test termination, are evident) is customary; the Bruce protocol is the most common. Submaximal tests that use a predetermined endpoint such as an age-predicted maximum heart rate are usual before discharge. The modified Bruce protocol is the most commonly used since it introduces two preliminary, less strenuous stages (Table 14.1).

Criteria for terminating an exercise test include:

horizontal or down-sloping ST segment depression greater than 2 mm, indicating ischaemia

marked drop in systolic blood pressure (>20 mmHg) indicating poor left ventricular function or severe coronary disease

serious arrhythmias, e.g. ventricular tachycardia

patient fatigue and/or excessive breathlessness at low workloads, which may simply indicate poor functional capacity but may also be suggestive of serious problems such as heart failure.

In general an exercise ECG test is considered to be negative if haemodynamic responses to the increasing workload are normal and the patient satisfactorily completes a workload equivalent to the second stage of the full Bruce protocol (7 METs). The test is considered positive if the patient is symptomatic at low workloads, if there are significant ECG changes or there is an inappropriate heart rate/blood pressure response to the incremental workload.

Table 14.1 Commonly used treadmill exercise protocols

Age-adjusted predicted maximal rates can be used (220 bpm minus age in years is one formula) and the training heart rate set at 60–75% of the predicted maximum; this is equivalent to 40–65% VO₂max. However, the standard deviation (SD) for maximal heart rate during exercise is ± 10 bpm and some individuals will, therefore, have an actual maximum heart rate 20 bpm higher or lower (2 SD above or below the population mean) than predicted. An alternative approach is to prescribe training at 40–65% of heart rate reserve (HRR – the difference between resting and maximal heart rate). This HRR approach (also known as the Karvonen method) is convenient since it is known that 40–65% of heart rate reserve is equivalent to about 40–65% of VO₂max (60–75% of maximal heart rate) although, across the entire range of fitness levels, it is more closely linked to the percentage of oxygen uptake reserve (VO₂R): i.e. the difference between resting oxygen consumption and maximal oxygen consumption (American College of Sports Medicine 2006). An example of the HRR method for calculating training heart rate is shown below for an individual with a resting heart rate of 60 bpm and maximal heart rate of 150 bpm.

150 − 60 = 90 (heart rate reserve, HRR)

Training heart rate = 40−65% of heart rate reserve + resting heart rate (RHR)

90 × 0.40 = 36 + 60 (RHR) = 96 bpm (40%)

90 × 0.65 = 59 + 60 (RHR) = 119 bpm (65%)

Note: The formula is intended for use with known maximal heart rates. In the absence of these data, the substitution of age-adjusted predicted maxima introduces the same potential for error as previously mentioned. Consequently, any prescription that is based on predicted maximal heart rates should be used in conjunction with a rating of perceived exertion scale (RPE).

Since the relationship between exercise intensity and the per cent of maximal heart rate is preserved in patients on beta-blockers, the above formula can be adopted for calculating a training heart rate for this group but the maximal or peak heart rate must be established from an exercise test performed on medication.

Use of rating of perceived exertion

Cardiorespiratory and metabolic variables are strongly related to perceived exertion, which is accepted as a valid and reproducible indicator of the intensity of steady-state exercise. Physiotherapists and exercise specialists working in a cardiac rehabilitation setting are recommended to familiarize themselves with the scales of perceived exertion developed by Borg (1998). The Borg 15-point scale and the Borg CR10 scale of perceived exertion, together with patient instructions, are published in the Appendix of Borg’s Perceived Exertion and Pain Scales (Borg 1998). In order to preserve the validity and reproducibility of these scales, their format should not be altered and the patient instructions should be closely followed.

On the 15-point scale a rating of 12–13 (equivalent to 3–4 on the Borg CR10 scale) corresponds to approximately 40% of heart rate reserve or VO₂max (60% HRmax). A rating of 15 on the 15-point scale (equivalent to 5–6 on the Borg CR10 scale) corresponds to approximately 65% of heart rate reserve or VO₂max (75% HRmax).

Use of metabolic equivalent values (METs)

Exercise may also be regulated by choice of activities according to their known MET (metabolic equivalent) values (for which tables are available in most exercise physiology texts). If an individual assesses walking at 3 miles per hour (mph) as 12–13 on the Borg RPE scale (corresponding to 60% of VO₂max), then activities of comparable MET value can be prescribed in the knowledge that they will present an appropriate training stimulus. Knowledge of MET values is also important in terms of excluding those activities that might pose a risk to certain individuals. Skipping (8–12 METs) or freestyle swimming (9–10 METs), for example, would be entirely inappropriate for someone with a peak capacity of 7 METs.

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