The exercise component of cardiac rehabilitation has evolved from the recognition that physical deconditioning occurs following MI and the knowledge that regular exercise protects against cardiovascular disease.⁸⁸ Physical inactivity increases the risk of developing coronary heart disease two fold.⁸⁹ National surveys of physical activity in Scotland confirm that inactivity is high in the general population.⁹⁰ Structured exercise as a therapeutic intervention is central to cardiac rehabilitation.^20,71,91,146 Daily exercise should also be encouraged as part of an 'active living' philosophy.⁹²

3.1 Benefits of exercise training

3.1.1 MORTALITY AND CARDIOVASCULAR OUTCOMES

Randomised trials distinguish between two types of exercise-based cardiac rehabilitation: exercise-only and exercise in addition to psychological and educational interventions, usually termed comprehensive cardiac rehabilitation.

A Cochrane review of men and women of all ages with previous MI, revascularisation or angina found that exercise-only cardiac rehabilitation reduced all cause mortality by 27%, cardiac death by 31% and a combined end point of mortality, non fatal myocardial infarction and revascularisation by 19%.⁹³ The benefits accrued over an average of 2.4 years. There was no effect on non fatal myocardial infarction alone and there was no apparent additional benefit from comprehensive cardiac rehabilitation. Most subjects were low risk middle aged men post MI. Patients with heart transplants, artificial valves and heart failure were excluded. Evidence level 1+

There are two possible explanations for the failure of comprehensive cardiac rehabilitation to show additional benefit. One is that exercise-only cardiac rehabilitation is likely to include psychological and educational support, even if this is not offered in a structured fashion. The other is that most of the exercise-only trials were conducted in the pre-thrombolytic era, whereas most of the comprehensive trials were published more recently. This means that the benefits in the comprehensive rehabilitation trials are likely to be additional to those of thrombolysis, prophylactic medication, and/or revascularisation.

3.1.2 PSYCHOLOGICAL AND OTHER OUTCOMES

There has been a wider acceptance in recent years that mortality and reinfarction are not the only methods of measuring the effectiveness of cardiac rehabilitation. Exercise alone has been shown to improve physical performance, muscle strength, and symptoms of breathlessness and angina. Comprehensive cardiac rehabilitation will in addition aid psychological function, social recovery, return to work, and biological risk factors.⁹¹

Exercise training should form a core element of cardiac rehabilitation programmes.

3.2 Safety issues

Most patients will benefit from and should be encouraged to undertake at least low to moderate intensity exercise. However, patients with clinically unstable cardiac disease or limiting co-morbid illness should be excluded from exercise training.

The incidence of serious adverse events during supervised exercise is low.^94,95 The most recent study of one rehabilitation centre documented four major complications (three cardiac arrests and one non fatal MI) over a nine year period.⁹⁶ There were no fatalities, giving a frequency of one major complication per 67,126 patient hours of exercise. All three cardiac arrests occurred in patients who had completed at least 12 weeks of exercise training and were enrolled in a maintenance programme.

3.3 Assessment before exercise training

For most patients, clinical risk stratification based on history, examination and resting ECG combined with a functional capacity test such as a shuttle walking test⁹⁷ (see section 3.3.1) or a six minute walking test⁹⁸ will be sufficient. Evidence level 4

High risk patients may be defined as those who have:

• experienced a myocardial infarction complicated by heart failure, cardiogenic shock and/or complex ventricular arrhythmias
• angina or breathlessness occurring at a low level of exercise, e.g. inability to complete the first four minutes of the shuttle walking test
• ST segment depression >=1 mm on resting ECG
• undergone exercise testing with marked ST depression >=2 mm or angina at <5 METS (e.g. 3 minutes of a Bruce protocol).
  Evidence level 4

Exercise testing and echocardiography are recommended to assess residual ischaemia and ventricular function respectively¹ but are not a necessary part of cardiac rehabilitation except for high intensity exercise or in high risk patients. Evidence level 4

Clinical risk stratification is sufficient for low to moderate risk patients undergoing low to moderate intensity exercise.

Exercise testing and echocardiography are recommended for high risk patients and/or high intensity exercise training (and to assess residual ischaemia and ventricular function where appropriate).

Functional capacity should be evaluated before and on completion of exercise training using a valid and reliable measure.

3.3.1 THE SHUTTLE WALKING TEST

The shuttle walking test was developed for patients with respiratory disease⁹⁹ but has recently been used to assess functional capacity before and after cardiac rehabilitation in patients who have undergone cardiac surgery^97,100 or pacemaker insertion,¹⁰¹ and in patients with chronic heart failure.^102,103 The shuttle walking test is a low cost low tech alternative to exercise testing that informs the rehabilitation team on a suitable exercise programme and appropriate training heart rate, and allows assessment of progress during cardiac rehabilitation without the need for cardiac technicians, physicians or expensive equipment. The shuttle walking test protocol is given in Box 1. Details of how to obtain copies of the tape are available on the SIGN website. Evidence level 4

Box 1

3.4 Staffing

There is no consensus on staffing levels for Phase 3 exercise programmes. Current UK guidelines recommend that two trained staff should be present at all times during exercise training with a patient to staff ratio of not more than 5:1.¹⁰⁴ Australian guidelines recommend a ratio of no more than 10 patients to one staff member.⁹¹ There is a similar lack of consensus on life support training: UK guidelines recommend basic life support training for all, provided at least one member of staff has advanced life support training,¹⁰⁴ whereas Australian guidelines make no such stipulation for patients undergoing low to moderate intensity exercise training.⁹¹ Evidence level 4

The ratio of patients to trained staff should be no more than 10:1 during exercise classes.

Staff with basic life support training and the ability to use a defibrillator are required for group exercise of low to moderate risk patients.

Immediate access to on-site staff (hospital emergency team) with advanced life support training is required for high risk patients and classes offering high intensity exercise training.

3.5 Location

A number of randomised trials^{77,105,106,107,108,109,110} and large observational studies^{15,111,112,113,114,115,116,117} have found that low to moderate intensity exercise for low to moderate risk patients can be provided as safely and as effectively in the home or community as in a hospital setting. Patients at high risk and those undergoing high intensity training should only exercise at venues with full resuscitation facilities and staff trained in advanced life support. Evidence level 1+, 2++, 2+

Low to moderate intensity exercise training can be undertaken as safely and effectively in the home and community as in a hospital setting for low to moderate risk patients.

Exercise training for high risk patients and for those who require high intensity exercise (see section 3.6.1) should be hospital-based or in a venue with full resuscitation facilities.

Patients exercising at home should have access to regular review and support by cardiac rehabilitation staff.

3.6 Exercise content

Cardio-respiratory fitness requires aerobic training of low to moderate intensity, and long duration with repetitive movement of large muscle groups. The frequency, intensity and duration of exercise can be varied to achieve the desired training effect. The individual's preference best determines the appropriate mode of activity. All trials included in a recent Cochrane review⁹³ were of aerobic exercise such as cycling, walking, jogging, rowing or calisthenics. In the UK, aerobic circuit training is traditionally used for group exercise training¹⁰⁴ and is an effective method for achieving a training heart rate. Exercise sessions should have:

• a 15-minute warm up period
• an aerobic conditioning phase of 20-30 minutes (resistance training, if appropriate, can be included after the conditioning phase)
• a 10-minute cool down period
• 5-10 minutes relaxation.

3.6.1 INTENSITY OF EXERCISE

Early studies of exercise-based cardiac rehabilitation randomised patients to high intensity exercise training plus usual care, or usual care alone.¹⁴⁶ Four randomised trials have since compared high intensity training versus low to moderate intensity training. Three found no differences in deaths or reinfarction, physical, psychological or social outcomes,^118,119 physical working capacity or quality of life at 12 months.¹²⁰ In one study, patients enrolled in a high intensity training group did have significantly greater improvements in maximal oxygen uptake and rest to maximal exercise ejection fraction at 12 months.¹⁵³ Evidence level 1+, 4

High intensity exercise training may be desirable for those whose work is physically demanding, and for younger men and women who wish to resume demanding sports. High intensity exercise involves training at a heart rate that is more than 75% of the maximum heart rate during a symptom limited exercise test, as indicated in Table 1. ^90,91,130 Although high intensity exercise rarely provokes ventricular tachycardia or myocardial infarction,^94,95 it is suggested that patients should undergo a symptom limited exercise test first.¹²¹ High risk patients should either be excluded from or carefully monitored during high intensity exercise.^{122,123,124,125,126} Evidence level 1+, 3, 4

Aerobic, low to moderate intensity exercise, designed to suit a range of fitness levels, is recommended for most patients undergoing exercise training.

3.6.2 FREQUENCY AND LENGTH OF PROGRAMME

Most early trials of exercise-based cardiac rehabilitation consisted of three exercise sessions per week for eight weeks or longer.^93,146 Twice weekly exercise has since been found to increase maximum physical working capacity to the same extent as thrice weekly exercise.¹²⁷ A further study has suggested that once weekly, hospital-based exercise plus two equivalent home-based exercise sessions is as effective in improving physical work capacity as thrice weekly hospital-based exercise.¹¹⁰ This suggests that incorporation of regular, sustained exercise into an individual's lifestyle is likely to be more important than the frequency or length of formal exercise training. Evidence level 1+, 4

The formal exercise component of cardiac rehabilitation should be offered at least twice a week for a minimum of eight weeks.

Once weekly group exercise with two equivalent home-based sessions improves exercise capacity as effectively as thrice weekly hospital-based exercise.

3.7 Monitoring of exercise training

Exercise intensity may be monitored either by perceived exertion using Borg's scale (see Table 1)¹²⁸ or by pulse monitor.¹⁰⁴ A perceived exertion scale allows quantification of the subjective intensity of exercise. Ratings on Borg's scale have been found to relate closely to other objective measures of exercise intensity, namely oxygen uptake and heart rate.¹²⁹ Evidence level 4

The aim is to enable patients to achieve a level of 'comfortable breathlessness'¹³⁰ while exercising, and so distinguish between high intensity and low to moderate intensity exercise. Patients can take several sessions to become familiar with and competent in the use of this scale. Levels of perceived exertion should only be used as a guide to exercise intensity, as cardiac patients may report significantly lower scores of perceived exertion at a given intensity of exercise when compared to age-matched controls.¹³¹ Pulse monitoring is best done by using pulse monitors, which may help patients until they are familiar with and competent in the use of the Borg scale. It is difficult to take one's own pulse while exercising, and this practice is not recommended. Evidence level 4

Exercise intensity should be monitored and adjusted by perceived exertion using the Borg scale or by pulse monitor.

Patients should be taught how perceived exertion can be used to regulate exercise intensity.

Table 1: Correlation of training level with perceived exertion and heart rate⁹¹

3.8 Resistance training

A key outcome of cardiac rehabilitation is to return patients to a fully active lifestyle. This requires muscle strength as well as aerobic endurance. Resistance (or strength) training improves muscular strength, cardiovascular function, coronary risk factors and psychological well being.¹⁴⁶ In most studies, low to moderate intensity resistance training (<70% maximum voluntary contraction) was incorporated after four weeks of supervised aerobic training,¹⁴⁶ but more recent studies have enrolled patients as early as four weeks post event.^132,133 Single set resistance training two or three times per week (where an exercise is performed as one set of 10-15 repetitions) is as effective and less time consuming than once weekly multiple set programmes (where the same muscle group is exercised two or more times at one session).¹³⁴ Evidence level 1+, 2+, 4

Low to moderate risk cardiac patients can undertake resistance training.

Patients may benefit from supervised aerobic training prior to resistance training to allow them to master the skills of self monitoring and regulating exercise intensity.

Blood pressure may increase more during resistance training than during aerobic training. Hypertensive patients should not be enrolled in such a programme until their blood pressure is well controlled.

3.9 Long term exercise training

See section 5.5.