Cardiac rehabilitation and exercise training
We read with interest the recent multicentre UK study by Sandercock and colleagues1 quantifying prescribed exercise volume and changes in cardiorespiratory fitness (CRF) involving 950 patients across four UK outpatient cardiac rehabilitation (CR) centres routinely performing CRF testing pre- and post-CR and with clinical practice consistent with professional body guidelines. The authors characterise low volume exercise training programmes across the four rehabilitation centres - with patients receiving a modal value of 8 exercise sessions (range 6-16). This appears in stark contrast to the international studies outlined in the author's earlier systematic review and evidence-based guidelines2. Although CRF improvements varied by rehabilitation centre and testing protocol (treadmill test protocol was a significant source of the between- trial heterogeneity), the overall improvement in CRF (0.52 METS) was only one third the mean estimate reported in their earlier meta-analysis (1.55 METs)2. The authors indicated that if representative of UK services, these low training volumes and small increases in CRF may partially explain the reported inefficacy of UK CR to reduce patient mortality and morbidity, as outlined by the RAMIT group3.
We agree with the assertion that lower exercise training volumes may be partly responsible for the lower than expected CRF values reported in the UK centres evaluated. Indeed, the CRF improvements within UK centres reported by Sandercock and colleagues1 are not consistent with data observed in our community-based CR investigations (Heartwatch, Leeds Leisure Services) using submaximal (85% age-predicted maximum heart rate) exercise testing protocols to evaluate short (3 month) and longer-term (15 month) community-based exercise training in a large, representative sample of patients with cardiovascular disease. We hereby report unpublished observations of 139 patients (79% males; mean age 62 (8) years); BMI 28 (4) kg*m-2; 62% on beta-blockers) who undertook 3 months of structured exercise-based community CR (undertaking a minimum of 2 circuit training sessions per week). Pre and post-CR exercise testing at the Heartwatch Centre was conducted on a Marquette treadmill using a specifically designed 2-minute stage incremental walking protocol4. The oxygen consumption at stages 5 and 6 (10 to 12 minutes duration) of the protocol was an estimated 25 to 29 ml?kg-1?min-1. Patients were encouraged to exercise up to 85% of age-predicted maximum heart rate (220?age) or a "very hard" rating of perceived exertion (RPE 17) using the Borg scale. Following 3 months exercise training, surrogate CRF variables including exercise duration (10.1 ? 2.5 min v 11.5 ? 2.7 min; P=0.0001) significantly improved. These improvements in submaximal CRF are consistent with our earlier reported observations5 among 154 non-diabetic CVD patients (89% male; aged 60 ?9 years; body mass index [BMI], 27?4 kg?m -2) who completed a further 12 months of exercise training. Self-reported exercise training compliance rates at 15 months, reported on clinical reassessment was 2.9 ?0.9 sessions per week. Exercise test results showed that submaximal treadmill duration increased from 10.1 to 12.2 minutes. These short and longer term improvements in CRF to graded walking represented an additional 2-minute stage of the incremental walking protocol4, corresponding to a 1.0 MET improvement in CRF.
We also feel that the methods used to estimate exercise training volumes and the impact this may have on exercise prescription may also be contributory factors in many UK-based CR programmes. The prescription of an appropriate exercise dose should be predicated on a clear appreciation of patient requirements and their physical characteristics including the degree of cardiac dysfunction and level of skeletal muscle wastage. Exercise intensity thresholds should be high enough to be effective but should be titrated within appropriate safety margins. Therefore, CRF should be assessed as accurately possible in cardiac populations. In the UK, there has arguably been a historical over-reliance on exercise prescription derived from indirect, submaximal assessments of exercise capacity, such as the incremental shuttle walk test (ISWT) and/or 6-minute walk tests (6-MWT) in patients undertaking CR. This observation was clearly evident in the recent publication by Dr Sandercock and colleagues1 who reported the use of these assessment modalities in four audited centres (treadmill and cycle ergometry were also used in two centres). Many UK centres will then use performance from submaximal tests to inform exercise training prescription relying solely on using predicted heart rate training zones and/or ratings of perceived exertion. Clearly, submaximal exercise test protocols do not rigorously evaluate the integrity of the cardiorespiratory system (a primary purpose of the exercise test). Therefore, it is possible that patient effort may be more variable in submaximal, self-paced tests such as the 6-MWT. Consequently, the widespread practice of submaximal exercise testing in the UK may be one of the reasons why CR programmes appear to be less effective.
In Europe and North America there is a much greater focus on "gold standard" techniques, including maximal exercise testing with metabolic gas exchange (cardiopulmonary exercise testing) which provide the preferred method for assessing CRF and prescribing exercise training in CR. Exercise prescription may be fine-tuned on the ventilatory anaerobic threshold or respiratory compensation point. There is overwhelming evidence indicating the superior prognostic value of ventilatory markers including peak oxygen uptake, VE/VCO2 slope, and exertional oscillatory ventilation, amongst others, especially in lower functional capacity groups such as chronic heart failure6. Ventilatory markers are rarely assessed and are seldom considered during exercise prescription in the majority of CR programmes in the UK.
Under certain circumstances, there may be a requirement to assess individual responses to exercise with submaximal testing protocols. For example, if the assessment of exercise capacity is undertaken outside a hospital setting (sporting or community centre); if a medical doctor is not available to supervise the maximal test; or when a large number of patients require assessment over a short time frame. If maximal exercise testing is to become more pervasive in the UK there will be a requirement for an initial capital outlay on equipment (though existing testing systems may be under-utilised in many Trusts around the country), and there will be a need for specialist staff training and on-going consumable costs. However, we should not lose perspective over the major objectives of CR, the Cinderella of cardiology services, and bear in mind the apparent under-prescription of exercise that seems to be common practice in UK centres. UK-based CR should not be run on a shoe-string budget. It has been long-established that increasing CRF reduces mortality and morbidity in secondary prevention settings7. There is a pressing need to adopt a more evidence-based approach to exercise prescription in patients undertaking CR in the UK.
Dr Lee Ingle & Professor Sean Carroll Department of Sport, Health & Exercise Science University of Hull Kingston-upon-Hull HU6 7RX United Kingdom
1. Sandercock GR, Cardoso F, Almodhy M, Pepera G. Cardiorespiratory fitness changes in patients receiving comprehensive outpatient cardiac rehabilitation in the UK: a multicentre study. Heart. 2012 Nov 24. [Epub ahead of print].
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