The importance of increasing exercise capacity during cardiac rehabilitation in heart failure: Optimising training to optimise prognosis

The first study indicating that cardiac rehabilitation could improve prognosis in heart failure patients was published in 1999 by Belardinelli et al.¹ In a rather small population of 110 patients, the authors showed that one year of moderate exercise training reduced mortality and readmission to hospital. This important finding was backed up by the ExTraMATCH Collaborative in 2004.² In their meta-analysis of nine trials of exercise training in chronic heart failure, including 395 patients in the exercise group and 405 patients in the control group, they found a reduction in mortality (primary endpoint) and a reduction in death or readmission to hospital (secondary endpoint) in favour of the exercise group.

Finally, HF-ACTION,³ the largest prospective study on the effects of exercise on mortality in chronic heart failure, confirmed a modest significant reduction for both all-cause mortality or hospitalisation and cardiovascular mortality or heart failure hospitalisation (after adjustment for highly prognostic predictors of the primary endpoint). In a subanalysis of the study, Keteyian et al.⁴ showed that exercise volume (expressed in metabolic equivalent-hours per week) was associated with the risk of events. Only a modest volume of exercise per week was sufficient to induce positive effects. Hamill et al.⁵ showed that patients who attended at least 36 sessions of cardiac rehabilitation had a decreased risk of death or myocardial infarction compared to patients attending 24 sessions or those attending 12 sessions. This effect was apparent in the subgroup of heart failure patients as well as for all cardiac patients included in the study.

The study by Sabbag et al.,⁶ published in a previous issue of the European Journal of Preventive Cardiology, examined the effect of cardiac rehabilitation on prognosis from a different aspect than the previous studies. The authors analysed how much the improvement in exercise capacity during cardiac rehabilitation could influence prognosis in heart failure patients. The authors retrospectively selected heart failure patients, who completed initial and follow-up exercise testing, from their cardiac rehabilitation programme between 2009 and 2016. The cohort of patients was divided into two groups with either low or high initial exercise capacity. Each of these two groups was further divided into groups of patients with minor or major improvement in exercise capacity. The primary outcome measured was a composite of first cardiac-related hospitalisation or all-cause mortality. The authors found the lowest rate of events in the group with high initial exercise capacity and major improvements. Intermediate outcome was observed if patients either had a high initial exercise capacity but showed only minor improvement or had a low initial exercise capacity but showed major improvement. Finally, patients with low initial exercise capacity and low improvement had the worst outcome. They also showed that there was a dose–response relationship between the improvement in exercise capacity and the decrease of risk. They found that every 5% increase in predicted exercise capacity resulted in a 10% reduction of risk for the primary endpoint. Finally, they showed that the final exercise capacity reached after rehabilitation was the most important determinant of the subsequent risk of adverse events. It was superior to initial exercise capacity or to the magnitude of improvement in exercise capacity.

The results of the study demonstrate the importance of exercising patients at adequate training loads in order to achieve optimal increases in exercise capacity. There is still an ongoing debate as to how to train heart failure patients most effectively. Various training intensities and modalities have been studied. While continuous moderate intensity training seems to be the best established training modality in heart failure patients, higher training intensities, used in an interval mode, have become increasingly popular during the past 10 years, especially since a small Norwegian study,⁷ including a total of 27 patients, found spectacular increases in peak oxygen consumption (VO_2peak) of 46% with high intensity interval training compared to only 14% with moderate continuous training. Other small studies seemed to confirm the larger improvements in exercise capacity by high intensity training over moderate training, although the effect they found was not quite as important. In addition, there were no major safety issues in these small cohorts⁸ with high interval training. The favourable results of these small studies were, however, not confirmed by the SMARTEX-HF study,⁹ the largest prospective study comparing high intensity to moderate training in heart failure patients, with both training regimens showing similar increases in VO_2peak.

Vromen et al.¹⁰ performed a meta-regression analysis on 17 unique articles and found that total energy expenditure (calculated as the product of exercise intensity × session duration × session frequency × programme duration) appeared to be the major predictor for improvement in exercise capacity in heart failure patients. This finding suggests that there is more than the ‘intensity factor’ that can be targeted to achieve optimal benefits.

Every healthcare professional involved in the training of cardiac patients, especially heart failure patients, should tailor exercise programmes individually to each patient, modulating and permanently adapting intensity, frequency, modality or duration to the best abilities of the patient, as stated in the latest European Society of Cardiology guidelines on cardiovascular disease prevention in clinical practice.¹¹ This way, an optimal improvement in exercise capacity should be obtained and prognosis enhanced. Finally, we have to bear in mind that heart failure patients who do not improve their exercise capacity and/or have a low exercise capacity at the end of cardiac rehabilitation, despite optimal training design, have a worse prognosis and should therefore be monitored carefully.^6,12

Declaration of conflicting interests

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author received no financial support for the research, authorship, and/or publication of this article.

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