Assessing the impact of the exercise component of cardiac rehabilitation
Creators: name: PRICE, Kym
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 420199
subject: Allied health and rehabilitation science not elsewhere classified
classificationCode: 420702
subject: Exercise physiology

description: The exercise prescription in cardiac rehabilitation and its effectiveness for inducing positive health benefits have been extensively studied in North America and Europe. However, there has been minimal research conducted in Australian cardiac rehabilitation programs. The studies described in this thesis comprise a total of 85 patients and investigated the current practice of exercise prescription in an outpatient cardiac rehabilitation program conducted at a single Australian hospital, that is prescribed according to the guidelines published by the National Heart Foundation.<br><br>

After reviewing the international cardiac rehabilitation guidelines, it was identified that recommendations in Australia are different to most other countries around the world. Australian recommendations are for light- to moderate-intensity aerobic exercise alongside resistance training. Guidelines from leading international cardiovascular scientific societies recommend a progression from moderate- to vigorous-intensity aerobic exercise over the course of the program with a greater emphasis on resistance training. In addition, Australian guidelines favour functional testing prior to exercise commencement rather than symptom limited exercise testing, and do not distinguish between different patient diagnoses. With this knowledge of the differences in the recommendations for exercise prescription in cardiac rehabilitation between Australian and international guidelines, it is therefore important to investigate if exercise prescribed in an Australian cardiac rehabilitation program adheres to recommendations and if it is effective for eliciting positive changes in cardiovascular risk factors. This information could then be utilised to guide the development of updated recommendations and/or guidelines for cardiac rehabilitation programs in Australia. <br><br>

Understanding the initial physical capacity of people attending cardiac rehabilitation is important to ensure the exercise prescription is individually tailored. The influence of the type of cardiac intervention received (surgical or non-surgical) and estimated cardiorespiratory fitness (CRF) on the initial aerobic exercise prescribed to individuals attending an Australian outpatient cardiac rehabilitation program was investigated. Estimated CRF was lower in surgically-treated compared with non-surgically treated individuals, and was higher in younger compared with older individuals who had received surgical intervention. However, the initial aerobic exercise intensity did not differ between the two categories of cardiac intervention received. The initial aerobic exercise prescription did not appear to consider estimated CRF, meaning that those with lower capacity were working at a higher relative intensity, potentially increasing the risk for adverse events. Routine graded exercise testing would enable individualised prescription of aerobic exercise intensity relative to current capabilities. <br><br>

Progression of prescribed exercise is important to facilitate improved physical capacity during cardiac rehabilitation. However, the Australian cardiac rehabilitation guidelines do not include recommendations on how or when exercise should be progressed. Progression of the prescribed exercise over the course of the cardiac rehabilitation program and whether exercise progression differed between cardiac intervention received, age or initial physical capacity were evaluated. Both aerobic exercise dose and resistance training load increased throughout the 12 cardiac rehabilitation sessions, by a mean of 49% and 174% respectively. The intensity of aerobic exercise was progressed rather than the duration, while both the weight lifted and the repetitions performed during resistance training increased. Exercise progression was influenced by initial CRF and grip strength. Individuals with the lowest CRF were prescribed aerobic exercise at the highest relative intensity (to their initial CRF) and did not significantly progress from the first session. The participants in the lowest tertile for initial hand grip strength similarly received less frequent increases in their resistance training than those with higher initial strength. Utilisation of information provided by routine graded exercise testing and formal strength testing prior to commencement would enable practitioners to prescribe higher initial aerobic exercise intensities and resistance training loads to patients with higher physical capacity and allow for adequate exercise progression for maximising possible improvements for all individuals. <br><br>

Maintenance of improvements in physical capacity and cardiovascular risk factors over the 12 months following completion of a cardiac rehabilitation program suggests achievement of more permanent lifestyle changes. Changes in physical capacity, cardiovascular risk factors and psychosocial health over the course of the cardiac rehabilitation program and the subsequent 12 months were investigated. Cardiorespiratory fitness improved by a mean of 16% and muscular strength by 8% over the course of the program, but did not improve further in the 12 months following completion of cardiac rehabilitation. No improvement in traditional cardiovascular risk factors, including blood pressure, body composition, lipid profile or blood glucose, was evident during the program, but self-reported symptoms of depression, physical functioning and self-efficacy improved significantly. These results suggest that although exercise prescription according to the Australian cardiac rehabilitation guidelines elicited improvements in physical capacity and psychosocial health, it may be inadequate to induce changes in traditional cardiovascular risk factors sufficient to reduce the risk of future cardiac events.<br><br>

Aerobic interval exercise is included as an alternative modality to continuous exercise in cardiac rehabilitation guidelines in some nations, but not Australia. However, there is currently insufficient evidence to support a consistent recommendation of an interval exercise protocol that is safe and effective for a cardiac rehabilitation population. A systematic review with meta-analyses assessed the effect of a single bout of interval exercise on cardiovascular responses (blood pressure, heart rate variability, and vascular function). Meta-analyses found that systolic blood pressure responses to interval exercise did not differ from responses to continuous exercise in the first hour following exercise. However, reductions in diastolic blood pressure and flow-mediated dilation, each of which are indicators of cardiovascular risk, were observed 10-15 minutes following interval exercise. The available evidence indicates that although interval exercise does not appear to convey significantly higher cardiovascular risk than continuous exercise after a single session of exercise, further investigation is required to establish the safety of interval exercise specifically within a cardiac rehabilitation population.<br><br>

The studies in this thesis highlight the need for a recommendation for graded exercise testing prior to commencement of cardiac rehabilitation in the Australian guidelines. Routine graded exercise testing would provide more detailed information to better enable exercise prescription to be individualised based on current capabilities, and allow for more consistent and appropriate exercise progression, for maximal health benefits.