Changes in cardiorespiratory fitness in cardiac rehabilitation patients: A meta-analysis

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Abstract

Background/objectives

Improving patients' cardiorespiratory fitness is an important therapeutic outcome in cardiac rehabilitation. The ability of cardiac rehabilitation to reduce mortality and morbidity has been evidenced through several meta-analyses. Whether cardiac rehabilitation can increase cardiorespiratory fitness and which factors may influence such gains are less well quantified.

Methods

We performed detailed literature searches of electronic databases and manually searched papers concerning changes in cardiorespiratory fitness in cardiac rehabilitation patients. We performed random-effects meta-analysis of mean improvements in cardiorespiratory fitness and subgroup analyses to determine potential sources of heterogeneity.

Results

Data from 31 studies produced 48 groups (n = 3827) with a mean improvement of 1.55 (95% CI 1.21–1.89) METs, (p < 0.001); equivalent to standardised effect size of ES = 0.97 (95% CI 0.80–1.13). As this value was highly heterogeneous (Q = 852, p < 0.001) we performed subgroup analyses on the effect size data. Gains in fitness were highest in patients receiving > 36 exercise sessions in studies where fitness was assessed using the Naughton Protocol. Patient characteristics associated with the highest fitness gains were age (being young) and sex (being male training in a male-only exercise group). Changes in fitness were unrelated to programme type (comprehensive or exercise-only), duration or study design. There was no association with patient's baseline fitness levels.

Conclusion

This is the first meta-analysis of changes in cardiovascular fitness in cardiac rehabilitation patients and shows clinically significant improvements in a large sample of patients from a variety of rehabilitation programmes. This analysis helps describe the characteristics of cardiac rehabilitation programmes which can increase patients' cardiorespiratory fitness.

Introduction

There is an abundance of high quality evidence for the effectiveness of cardiac rehabilitation as a therapeutic intervention to reduce all cause mortality, cardiovascular mortality and morbidity [[1], [2], [3], [4], [5], [6]]. Much of the reduction in mortality and morbidity can be attributed to the positive influence that cardiac rehabilitation can have on cardiovascular risk factors such as smoking, hypertension and hypercholesterolemia [7].

In addition to adding years to the life of cardiac patients, it has also been proposed that rehabilitation should add ‘life to years’ [8]. Whilst pharmacotherapy can effectively modify many risk factors, exercise-based rehabilitation can increase functional capacity, mobility and independence by improving patients' cardiorespiratory fitness (herein fitness). Increased fitness is independently associated with improved quality of life in cardiac patients [9] and fitness is an excellent prognostic marker for future cardiovascular events [[10], [11], [12]]. Increases in cardiorespiratory fitness observed in patients during rehabilitation are closely associated with the reported reductions in mortality and morbidity [[13], [14], [15], [16], [17], [18], [19]]. Despite recognition of the clinical importance of fitness in cardiac patients, only limited attempts to synthesise the literature in this have been made [5], [20].

Recently, Conn et al. [5] found a significant improvement in physical activity levels of wide range of cardiac patients. The authors also meta-analysed changes in fitness as a secondary outcome. This analysis largely concentrated on quantifying standardised differences between post-test groups from randomised controlled trials. Whilst this approach ensured data quality it excluded the type of cohort-design and observational studies often performed in the more naturalistic setting of clinical practice. The effectiveness of CR as a therapy makes it unethical to withhold it from patients [21], making cohort-design studies increasingly necessary and common. The inclusion criteria that exercise testing be used as a behaviour change mechanism restricted the available studies in the meta-analysis of Conn et al. [5]. These authors were unable to perform subgroup analysis to determine which features of exercise (frequency, intensity, duration, modality) influenced changes in fitness. Whilst the effect size for change in physical activity was insightfully converted to energy expenditure (1984 kcal·week 1) there was no common-language estimate for gains in fitness such as in Vo2peak (ml·kg 1·min 1) or metabolic equivalents (METs).

The aim of the present study was to determine the overall increase in fitness observed in CR studies expressed in easily interpreted units (METs) which are potentially more useful to clinicians than standardised effect sizes. The second aim was to determine patient characteristics and programme features including exercise dose information associated with changes in fitness. The latter aim was designed to provide further guidance to clinicians in designing and refining cardiac rehabilitation provision to maximise patients' fitness gains.

Section snippets

Search strategy

Three authors independently searched PubMed, Ovid, Web of Science and The NIH library. Using broad search terms: exercise, cardiac (or cardiovascular) rehabilitation, training, functional capacity, fitness (cardiovascular fitness), Vo2peak, Vo2max. Initial results produced 7104 potential studies for review. Our aim was to perform an analysis on outpatient cardiac rehabilitation programmes provided to the ‘core’ cardiovascular patient population. To narrow the search terms we limited the date

Results

The overall effect for CR interventions of on fitness measures in metabolic equivalents (METs) is shown in Fig. 1. The 31 studies yielded 48 separate groups which had a mean pre- vs. post-test difference in fitness of 1.55 (95% CI 1.21–1.89) METs which was highly significant (p < 0.001). Using a random effects model, the effect size for the standardised mean difference in pre- vs. post-test fitness was: ES = 0.97 (95% CI 0.80–1.13). This difference was statistically significant (p < 0.0001) but was

Discussion

Cardiac rehabilitation is acknowledged as an effective intervention to reduce mortality and morbidity in patients with variety of cardiovascular diseases [[1], [2], [3], [4], [5]]. The earliest meta-analysis on the topic exclusively contained studies which only used exercise training as an intervention and despite the increase in comprehensive CR programmes exercise training remains a mainstay of most rehabilitation programmes [[55], [56], [57], [58], [59], [60], [61]].

It is agreed that

Conclusions and limitations

Previous meta-analyses have confirmed the efficacy of cardiac rehabilitation as a treatment to reduce patient mortality and morbidity. Rehabilitation programmes produce these reductions through the modification of cardiovascular disease risk factors and by promoting gains in cardiorespiratory fitness. Higher cardiorespiratory fitness is associated with reduced risk of cardiovascular mortality and morbidity, as is the magnitude of gains in fitness due to exercise training.

A recent meta-analysis

Acknowledgement

The authors of this manuscript have certified that they comply with the principles of ethical publishing in the International Journal of Cardiology.

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