Effect of exercise on endothelial function in heart transplant recipients: systematic review and meta-analysis

A Review of High-Intensity Interval Training in Heart Transplant Recipients: Current Knowledge and Future Perspectives

OBJECTIVE

This review reports how exercise-based rehabilitation strategies have developed over the past decades, and it specifically focuses on the effectiveness, safety, and implementation of high-intensity interval training (HIIT). It provides an overview of the historical progression, main research findings, and considerations surrounding HIIT as the preferred exercise modality for recipients of heart transplant (HTx).

REVIEW METHODS

The review includes a timeline of studies spanning from 1976-2023. The 2017 Cochrane systematic review on exercise-based cardiac rehabilitation in recipients of HTx serves as the main knowledge base (≥2015). Additionally, literature searches in PubMed/Medline and ClinicalTrials.gov have been performed, and all reviews and studies reporting the effects of moderate- to high-intensity exercise in recipients of HTx, published in 2015 or later have been screened.

SUMMARY

High-intensity interval training has gained prominence as an effective exercise intervention for recipients of HTx, demonstrated by an accumulation of performed studies in the past decade, although implementation in clinical practice remains limited. Early restrictions on HIIT in HTx recipients lacked evidence-based support, and recent research challenges these previous restrictions. High-intensity interval training results in greater improvements and benefits compared with moderate-intensity continuous training in the majority of studies. While HIIT is now regarded as generally suitable on a group level, individual assessment is still advised. The impact of HIIT involves reinnervation and central and peripheral adaptations to exercise, with variations in recipent responses, especially between de novo and maintenance recipients, and also between younger and older recipients. Long-term effects and mechanisms behind the HIIT effect warrant further investigation, as well as a focus on optimized HIIT protocols and exercise benefits.

Impact of Exercise Training Interventions on Flow-Mediated Dilation in Adults: An Umbrella Review

BACKGROUND

Dysfunction of the endothelium is a key precursor of cardiovascular disease. Endothelial function, as assessed via the flow-mediated dilation test, is attenuated with chronic disease (e.g., type 2 diabetes mellitus, hypertension). Exercise training may mitigate this dysfunction and promote better vascular health.

OBJECTIVE

The main objective of this umbrella review was to determine the impact of exercise training on flow-mediated dilation in healthy adults and those with chronic disease.

METHODS

Studies were included if they conducted a systematic review and/or meta-analysis on flow-mediated dilation responses to exercise interventions in adults. Sources were searched in January 2022 and included Scopus, EMBASE, MEDLINE, CINAHL, and Academic Search Premier. National Institutes of Health quality assessment tools were used. The results were presented narratively.

RESULTS

Twenty-seven systematic reviews, including 19 meta-analyses, (total: 5464 unique participants, 2181 reported unique female individuals) met the inclusion criteria. The average overall quality of included reviews was 8.8/11. The quality of studies within each included review varied from low to moderate using a variety of quality assessment scales. Reviews were conducted in healthy adults (n = 9, meta-analyses = 6), as well as those with type 2 diabetes (n = 5, meta-analyses = 4), cardiovascular conditions [i.e., conditions that impact the cardiovascular system, but excluding samples of only type 2 diabetes] (n = 11, meta-analyses = 7), and other chronic conditions (n = 2, meta-analyses = 2). Overall, the included reviews provided evidence that the type of training to optimally improve FMD may vary based on disease condition. Specifically, the evidence suggests that healthy adults benefitted most from higher intensity aerobic training and/or more frequent low-to-moderate resistance training. In addition, adults with type 2 diabetes benefitted most from low-intensity resistance or aerobic exercise training, whereas those with cardiovascular conditions should consider engaging in high-intensity aerobic training to improve endothelial function.

CONCLUSIONS

This information may help guide the design of specific exercise programs or recommendations for adults with chronic conditions.

Exercise training in heart transplantation

Heart transplantation remains the gold standard in the treatment of end-stage heart failure (HF). Heart transplantation patients present lower exercise capacity due to cardiovascular and musculoskeletal alterations leading thus to poor quality of life and reduction in the ability of daily self-service. Impaired vascular function and diastolic dysfunction cause lower cardiac output while decreased skeletal muscle oxidative fibers, enzymes and capillarity cause arteriovenous oxygen difference, leading thus to decreased peak oxygen uptake in heart transplant recipients. Exercise training improves exercise capacity, cardiac and vascular endothelial function in heart transplant recipients. Pre-rehabilitation regular aerobic or combined exercise is beneficial for patients with end-stage HF awaiting heart transplantation in order to maintain a higher fitness level and reduce complications afterwards like intensive care unit acquired weakness or cardiac cachexia. All hospitalized patients after heart transplantation should be referred to early mobilization of skeletal muscles through kinesiotherapy of the upper and lower limbs and respiratory physiotherapy in order to prevent infections of the respiratory system prior to hospital discharge. Moreover, all heart transplant recipients after hospital discharge who have not already participated in an early cardiac rehabilitation program should be referred to a rehabilitation center by their health care provider. Although high intensity interval training seems to have more benefits than moderate intensity continuous training, especially in stable transplant patients, individualized training based on the abilities and needs of each patient still remains the most appropriate approach. Cardiac rehabilitation appears to be safe in heart transplant patients. However, long-term follow-up data is incomplete and, therefore, further high quality and adequately-powered studies are needed to demonstrate the long-term benefits of exercise training in this population.

Exercise training modalities for heart transplant recipients: a systematic review and network meta-analysis protocol

INTRODUCTION

Heart transplantation is the gold standard treatment for selected patients with end-stage heart failure. Although this procedure can improve quality and prolong life expectancy, several of these patients persist with decreased exercise tolerance. Evidence suggests that exercise training can bring multifactorial benefits to heart transplant (HTx) recipients. However, it is unclear that exercise modality should be preferred. Therefore, the aim of this systematic review and network meta-analysis is to compare the efficacy and safety of different training modalities in HTx recipients.

METHODS AND ANALYSIS

We will perform a comprehensive literature search in PubMed/MEDLINE, Embase, The Cochrane Library, CINAHL, Scopus, SportDISCUS, Web of Science Core Collection and PEDro from inception until November 2020. Two registries (ClinicalTrials.gov and REBEC) will also be searched for potential results in unpublished studies. There will be no restriction on language, date of publication, publication status or sample size. We will include randomised controlled trials enrolling adult HTx recipients with the presence of at least one exercise training group, which might be compared with another training modality and/or a non-exercise control group for a minimum of 4 weeks of intervention. The primary outcomes will be peak oxygen consumption and occurrence of adverse events. As secondary outcomes, the interaction between pulmonary ventilation, pulmonary perfusion and cardiac output, oxygen uptake efficiency slope, heart rate response, oxygen pulse, peak blood pressure and peak subjective perception of effort. In addition, we will evaluate the 6 min walking distance, health-related quality of life, endothelial function, muscle strength, body fat percentage and lean mass. Risk of bias will be assessed using the Cochrane RoB V.2.0 tool, and we plan to use the Confidence in Network Meta-Analysis tool to assess confidence in the results. All materials (raw data, processed data, statistical code and outputs) will be shared in a public repository.

ETHICS AND DISSEMINATION

Given the nature of this study, no ethical approval will be required. We believe that the findings of this study may show which is the most efficacious and safe physical training modality for HTx recipients. The completed systematic review and network meta-analysis will be submitted to a peer-reviewed journal.

PROSPERO REGISTRATION NUMBER

CRD42020191192.