Muscular exercise capacity and body fat predict VO(2peak) in heart transplant recipients

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 Modalities on Peripheral and Central Components of Cardiorespiratory Capacity in Heart Transplantation Patients: A Systematic Review and Meta-Analysis

Background and Objectives: To analyze the effects of aerobic, resistance, and combined training on peripheral and central components related to cardiorespiratory capacity after HTx. Materials and Methods: No time restriction was applied for study inclusion. MEDLINE/PubMed; EMBASE, CENTRAL, and PEDro databases were investigated. Studies reporting heart transplanted patients older than 19 years following aerobic, resistance, and combined training according. The outcomes included: V′O₂ peak, VE/V’CO₂ slope, heart rate (HR peak), systolic and diastolic blood pressure (SBP and DBP peak), maximum repetition test(1RM), sit-to-stand test, and flow-mediated dilation (FMD). The studies were selected by consensus. Four hundred ninety-two studies initially met the selection criteria. Cochrane handbook was used for abstracting data and assessing data quality and validity. Independent extraction by two observers was applied. Results: Isolated aerobic training leads to a greater increase in V′O₂ peak than combined training compared to the control group (p < 0.001, I2 = 0%). However, no significant differences were found in the subgroup comparison (p = 0.19, I2 = 42.1%). HR peak increased similarly after aerobic and combined training. High-intensity interval training (HIIT) was better than moderate continuous intensity to increase the V′O₂ after long term in HTx. Still, there is scarce evidence of HIIT on muscle strength and FMD. No change on VE/V’CO₂ slope, FMD, and SBP, DBP peak. 1RM and the sit-to-stand test increased after resistance training (p < 0.001, I2 = 70%) and CT (p < 0.001, I2 = 0%) when compared to control. Conclusions: Aerobic and combined training effectively improve VO₂ peak and muscle strength, respectively. HIIT seems the better choice for cardiorespiratory capacity improvements. More studies are needed to examine the impact of training modalities on VE/V’CO₂ slope and FMD.

Body composition and maximal exercise capacity after heart transplantation

Aims

Maximal exercise capacity as measured by peak oxygen consumption (pVO₂) in cardiopulmonary exercise testing (CPET) of heart transplant recipients (HTR) is limited to a 50–70% level of healthy age‐matched controls. This study investigated the relationship between body composition and pVO₂ during the first decade post‐transplant.

Methods and results

Body composition was determined by dual‐energy X‐ray absorptiometry (DXA) and pVO₂ by CPET in 48 HTR (n = 38 males; mean age 51 ± 12 years). A total of 95 assessments were acquired 1–9 years post‐transplant, and the results of four consecutive periods were compared [Period 1: 1–2 years (n = 25); 2: 3–4 years (n = 23); 3: 5–6 years (n = 23); 4: 7–9 years (n = 24)]. Linear regression analysis analysed the correlation between pVO₂ and pairs of appendicular lean mass (ALM) and fat mass (FM). The relation between ALM and daily dose of calcineurin inhibitor (CNI) was explored using partial correlation controlling for age, gender, and height. pVO₂ increased from 0.98 (0.34) to 1.35 (0.35) L/min (P < 0.01) between Periods 1 and 4 corresponding to 54.5–63.3% of predicted value. Peak heart rate (HR) raised from 115 ± 19 to 131 ± 23 b.p.m. (P = 0.05), and anaerobic threshold (AT = VO₂ achieved at AT) increased from 0.57 (0.18) to 0.83 (0.35) L/min (P < 0.01) between Periods 1 and 3. Median FM normalized to height² (FMI) always remained elevated (>8.8 kg/m²). ALM normalized to body mass index increased from 0.690 (0.188) to 0.848 (0.204) m² (P = 0.02) between Periods 1 and 4, explaining 45% of the variance of pVO₂ (R² = 0.455; P < 0.001). Eighty‐one per cent of the variance of pVO₂ (R² = 0.817; P < 0.001) in multiple regression was explained by AT (β = 0.488), ALM (β = 0.396), peak HR (β = 0.366), and FMI (β = −0.181). ALM was negatively correlated with daily CNI dose (partial R = −0.258; P = 0.01).

Conclusions

After heart transplantation, the beneficial effect of peripheral skeletal muscle gain on pVO₂ is opposed by increased FM. Our findings support lifestyle efforts to fight adiposity and CNI dose reduction in the chronic stable phase to favour positive adaptation of peripheral muscle mass.

Heart rate kinetics during standard cardiopulmonary exercise testing in heart transplant recipients: a longitudinal study

AIMS

Heart transplantation (HTx) results in complete autonomic denervation of the donor heart, causing resting tachycardia and abnormal heart rate (HR) responses to exercise. We determined the time course of suggestive cardiac reinnervation post HTx and investigated its clinical significance.

METHODS AND RESULTS

Heart rate kinetics during standard cardiopulmonary exercise testing at 2.5-5 years after HTx was assessed in 58 patients. According to their HR increase 30 s after exercise onset, HTx recipients were classified as denervated (slow responders: <5 beats per minute [b.p.m.]) or potentially reinnervated (fast responders: ≥5 b.p.m.). Additionally, in 30 patients, longitudinal changes of maximal oxygen consumption and HR kinetics were assessed during the first 15 post-operative years. At 2.5-5 years post HTx, 38% of our study population was potentially reinnervated. Fast responders were significantly younger (41 ± 15 years) than slow responders (53 ± 13 years, P = 0.003) but did not differ with regard to donor age, immunosuppressive regime, cardiovascular risk factors, endomyocardial biopsy, or vasculopathy parameters. While HR reserve (56 ± 20 vs. 39 ± 15 b.p.m., P = 0.002) and HR recovery after 60 s (15 ± 11 vs. 5 ± 6 b.p.m., P < 0.001) were greater in fast responders, resting HR, peak HR of predicted, and peak oxygen consumption of predicted were comparable.

CONCLUSIONS

Signs of reinnervation occurred mainly in younger patients. Maximal oxygen consumption was independent of HR kinetics.

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.

Long-term effects of high-intensity training vs moderate intensity training in heart transplant recipients: A 3-year follow-up study of the randomized-controlled HITTS study

The randomized controlled High-Intensity Interval Training in De Novo Heart Transplant Recipients in Scandinavia (HITTS) study compared 9 months of high-intensity interval training (HIT) with moderate intensity continuous training in de novo heart transplant recipients. In our 3-year follow-up study, we aimed to determine whether the effect of early initiation of HIT on peak oxygen consumption (VO_2peak ) persisted for 2 years postintervention. The study's primary end point was the change in VO_2peak (mL/kg/min). The secondary end points were muscle strength, body composition, heart rate response, health-related quality of life, daily physical activity, biomarkers, and heart function. Of 78 patients who completed the 1-year HITTS trial, 65 entered our study and 62 completed the study tests. VO_2peak increased from baseline to 1 year and leveled off thereafter. During the intervention period, the increase in VO_2peak was larger in the HIT arm; however, 2 years later, there was no significant between-group difference in VO_2peak . However, the mean change in the anaerobic threshold and extensor muscle endurance remained significantly higher in the HIT group. Early initiation of HIT after heart transplantation appears to have some sustainable long-term effects. Clinical trial registration number: NCT01796379.

Cardiac rehabilitation program improves exercise capacity in heart transplantation recipients regardless of marginal donor factors

Cardiac rehabilitation (CR) is recommended to improve exercise capacity after heart transplantation (HTx); however, the effects of marginal donor factors are unclear. Forty-one recipients participated in a 3-month CR program early after HTx (mean age 39 ± 14 years; 88% male). Patients were divided into marginal (≥ 2 marginal donor factors; n = 24) and control groups (< 2 marginal donor factors; n = 17). We examined donor and recipient factors related to change in peak oxygen uptake (peak VO₂) during the CR program using multiple linear regression analysis. Baseline characteristics were similar between groups, although the mean age was higher in the marginal group (43 ± 13 vs. 34 ± 14 years, p = 0.043). Peak VO₂ and knee extensor muscular strength (KEMS) improved significantly in both groups (p < 0.05), but there were no observed inter-group differences. Multiple analysis revealed change in KEMS (β = 0.52, 95% CI = 0.023-1.01) as an independent predictor of change in peak VO₂ after adjustment for recipients' age, sex, and CR attendance frequency (adjusted R² = 0.25, p = 0.0084), whereas marginal donor factors were not a predictor (p = 0.76). The CR program improved exercise capacity in HTx recipients regardless of marginal donor factors, suggesting that recipients of marginal donor hearts should be referred to CR programs.

Effect of high-intensity interval training in young heart transplant recipients: results from two randomized controlled trials

Background

Little is known about the effect of exercise in young heart transplant recipients, and results on group level is lacking. This study summarizes the findings of the youngest participants in two previous randomized controlled trials.

Method

This is a hypothesis-generating study reporting the main results from the youngest participants in two larger randomized controlled trials investigating the effect of high-intensity interval training (HIT). The article summarizes the main results from 28 young participants (< 40 year of age) who have participated in two previous studies which evaluated the effect of HIT vs. controls in adult heart transplant recipients. One of the studies included de novo heart transplant recipients and the other included maintenance heart transplant recipients.All study tests were performed in-hospital, in the specialist health care setting, but the exercise intervention was carried out locally, in cooperation with the primary health care. In both studies the exercise intervention lasted for 9-12 months. In one study, HIT (85-95% of peak effort) was compared to controls (no specific intervention), and in the other study HIT was compared to moderate, continuous exercise (MICT, 60-80% of peak effort). The main outcome measure was peak oxygen uptake (VO_2peak) and a secondary endpoint was muscle strength.

Results

The summarized findings from the youngest heart transplant recipients in these two studies demonstrated mainly that the improvement in peak oxygen uptake among the younger recipients (< 40 years) was much larger (4.7 vs. 1.2 ml/kg/min and 7.0 vs. 2.2 ml/kg/min) compared to the improvement among the older recipients (≥ 40 years), and in accordance with results from adult heart transplant populations: HIT, compared to MICT, induced the largest improvement in peak oxygen consumption, also in the younger heart transplant recipients.

Conclusions

These results suggest that young heart transplant recipients have a greater effect of HIT than of MICT and may also suggest that younger recipients benefit more from high-intensity interval training than their older co-patients. However, larger randomized studies focusing on the young heart transplant population is strongly needed to confirm this hypothesis.

Trial registration

Clinical trial registrations: NCT01796379 and NCT01091194.

Effect of High-Intensity Interval Training in De Novo Heart Transplant Recipients in Scandinavia

BACKGROUND

There is no consensus on how, when, or at what intensity exercise should be performed after heart transplantation (HTx). We have recently shown that high-intensity interval training (HIT) is safe, well tolerated, and efficacious in the maintenance state after HTx, but studies have not investigated HIT effects in the de novo HTx state. We hypothesized that HIT could be introduced early after HTx and that it could lead to clinically meaningful increases in exercise capacity and health-related quality of life.

METHODS

This multicenter, prospective, randomized, controlled trial included 81 patients a mean of 11 weeks (range, 7-16 weeks) after an HTx. Patients were randomized 1:1 to 9 months of either HIT (4×4-minute intervals at 85%-95% of peak effort) or moderate-intensity continuous training (60%-80% of peak effort). The primary outcome was the effect of HIT versus moderate-intensity continuous training on the change in aerobic exercise capacity, assessed as the peak oxygen consumption (Vo₂peak). Secondary outcomes included tolerability, safety, adverse events, isokinetic muscular strength, body composition, health-related quality of life, left ventricular function, hemodynamics, endothelial function, and biomarkers.

RESULTS

From baseline to follow-up, 96% of patients completed the study. There were no serious exercise-related adverse events. The population comprised 73% men, and the mean±SD age was 49±13 years. At the 1-year follow-up, the HIT group demonstrated greater improvements than the moderate-intensity continuous training group; the groups showed significantly different changes in the Vo₂peak (mean difference between groups, 1.8 mL·kg^-1·min^-1), the anaerobic threshold (0.28 L/min), the peak expiratory flow (11%), and the extensor muscle exercise capacity (464 J). The 1.8-mL·kg^-1·min^-1 difference was equal to ≈0.5 metabolic equivalents, which is regarded as clinically meaningful and relevant. Health-related quality of life was similar between the groups, as indicated by results from the Short Form-36 (version 2), Hospital Anxiety and Depression Scale, and a visual analog scale.

CONCLUSIONS

We demonstrated that HIT was a safe, efficient exercise method in de novo HTx recipients. HIT, compared with moderate-intensity continuous training, resulted in a clinically significantly greater change in exercise capacity based on the Vo₂peak values (25% versus 15%), anaerobic threshold, peak expiratory flow, and muscular exercise capacity.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov . Unique identifier NCT01796379.

Clinical and Rehabilitative Predictors of Peak Oxygen Uptake Following Cardiac Transplantation

The measurement of peak oxygen uptake (VO_2peak) is an important metric for evaluating cardiac transplantation (HTx) eligibility. However, it is unclear which factors (e.g., recipient demographics, clinical parameters, cardiac rehabilitation (CR) participation) influence VO_2peak following HTx. Consecutive HTx patients with cardiopulmonary exercise testing (CPET) between 2007–2016 were included. VO_2peak was measured from CPET standard protocol. Regression analyses determined predictors of the highest post-HTx VO_2peak (i.e., quartile 4: VO_2peak > 20.1 mL/kg/min). One hundred-forty HTx patients (women: n = 41 (29%), age: 52 ± 12 years, body mass index (BMI): 27 ± 5 kg/m²) were included. History of diabetes (Odds Ratio (OR): 0.17, 95% Confidence Interval (CI): 0.04–0.77, p = 0.021), history of dyslipidemia (OR: 0.42, 95% CI: 0.19–0.93, p = 0.032), BMI (OR: 0.90, 95% CI: 0.82–0.99, p = 0.022), hemoglobin (OR: 1.29, 95% CI: 1.04–1.61, p = 0.020), white blood cell count (OR: 0.81, 95% CI: 0.66–0.98, p = 0.033), CR exercise sessions (OR: 1.10, 95% CI: 1.04–1.15, p < 0.001), and pre-HTx VO_2peak (OR: 1.17, 95% CI: 1.07–1.29, p = 0.001) were significant predictors. Multivariate analysis showed CR exercise sessions (OR: 1.10, 95% CI: 1.03–1.16, p = 0.002), and pre-HTx VO_2peak (OR: 1.16, 95% CI: 1.04–1.30, p = 0.007) were independently predictive of higher post-HTx VO_2peak. Pre-HTx VO_2peak and CR exercise sessions are predictive of a greater VO_2peak following HTx. These data highlight the importance of CR exercise session attendance and pre-HTx fitness in predicting VO_2peak post-HTx.

Clinical features and determinants of VO2peak in de novo heart transplant recipients

AIM

To study exercise capacity and determinants of early peak oxygen consumption (VO_2peak) in a cohort of de novo heart transplant (HTx) recipients.

METHODS

To determine possible central (chronotropic responses, cardiopulmonary and hemodynamic function) and peripheral factors (muscular exercise capacity and body composition) predictive of VO_2peak, a number of different measurements and tests were performed, as follows: Cardiopulmonary exercise testing (CPET) was performed mean 11 wk after surgery in 81 HTx recipients > 18 years and was measured with breath by breath gas exchange on a treadmill or bicycle ergometer. Metabolic/respiratory measures include VO_2peak and VE/VCO₂ slope. Additional measures included muscle strength testing, bioelectrical impedance analysis, echocardiography, blood sampling and health-related quality of life. Based on the VO_2peak (mL/kg per minute) median value, the study population was divided into two groups defined as a low-capacity group and a high-capacity group. Potential predictors were analyzed using multiple regression analysis with VO_2peak (L/min) as the dependent variable.

RESULTS

The mean ± standard deviation (SD) age of the total study population was 49 ± 13 years, and 73% were men. This de novo HTx cohort demonstrated a median VO_2peak level of 19.4 mL/kg per min at 11 ± 1.8 wk post-HTx. As compared with the high-capacity group, the low-capacity group exercised for a shorter time, had lower maximal ventilation, O₂ pulse, peak heart rate and heart rate reserve, while the VE/VCO₂ slope was higher. The low-capacity group had less muscle strength and muscular exercise capacity in comparison with the high-capacity group. In order of importance, O₂ pulse, heart rate reserve, muscular exercise capacity, body mass index, gender and age accounted for 84% of the variance in VO_2peak (L/min). There were no minor or major serious adverse events during the CPET.

CONCLUSION

Although there is great individual variance among de novo HTx recipients, early VO_2peak measures appear to be influenced by both central and peripheral factors.

Cardiopulmonary, biomarkers, and vascular responses to acute hypoxia following cardiac transplantation

Previous studies have suggested good adaptation of cardiac transplant (CTx) recipients to exposure to a high altitude. No studies have investigated the cardiopulmonary and biomarker responses to acute hypoxic challenges following CTx. Thirty-six CTx recipients and 17 age-matched healthy controls (HC) were recruited. Sixteen (16) patients (42%) had cardiac allograft vasculopathy (CAV). Cardiopulmonary responses to maximal and submaximal exercise at 21% O₂ , 20-minutes hypoxia (11.5% O₂ ), and following a 10-minute exposure to 11.5% O₂ using 30% of peak power output were completed. Vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), suppression of tumorigenicity 2 (ST2) were measured at baseline and at peak stress. Endothelial peripheral function was assessed using near-infrared spectroscopy. Compared with HC, CTx presented a lesser O₂ desaturation both at rest (-19.4 ± 6.8 [CTx] vs -24.2 ± 6.0% O₂ [HC], P < 0.05) and following exercise (-23.2 ± 4.9 [CTx] vs -26.2 ± 4.7% O₂ [HC], P < 0.05). CTx patients exhibited a significant decrease in peak oxygen uptake. IL-6 and VEGF levels were significantly higher in CTx recipients in basal conditions but did not change in response to acute stress. CTx patients exhibit a favorable ventilatory and overall response to hypoxic stress. These data provide further insights on the good adaptability of CTx to exposure to high altitude.

High-Intensity Interval Training in Heart Transplant Recipients: A Systematic Review with Meta-Analysis

Heart transplantation (HTx) is considered an efficient and gold-standard procedure for patients with end-stage heart failure. After surgery, patients have lower aerobic power (VO2max) and compensatory hemodynamic responses. The aim of the present study was to assess through a systematic review with meta-analysis whether high-intensity interval training (HIIT) can provide benefits for those parameters. This is a systematic review with meta-analysis, which searched the databases and data portals PubMed, Web of Science, Scopus, Science Direct and Wiley until December 2016 (pairs). The following terms and descriptors were used: "heart recipient" OR "heart transplant recipient" OR "heart transplant" OR "cardiac transplant" OR "heart graft". Descriptors via DeCS and Mesh were: "heart transplantation'' OR "cardiac transplantation". The words used in combination (AND) were: "exercise training" OR "interval training" OR "high intensity interval training" OR "high intensity training" OR "anaerobic training" OR "intermittent training" OR "sprint training". The initial search identified 1064 studies. Then, only those studies assessing the influence of HIIT on the post-HTx period were added, resulting in three studies analyzed. The significance level adopted was 0.05. Heart transplant recipients showed significant improvement in VO2peak, heart rate and peak blood pressure in 8 to 12 weeks of intervention.

Cholinesterase levels predict exercise capacity in cardiac recipients early after transplantation

PURPOSE

Although cardiac rehabilitation is recommended for patients early after heart transplantation (HTx), adequate exercise effect cannot always be obtained, partly because in patients with chronic heart failure, exercise capacity is reduced due to malnutrition while waiting for HTx. This study aimed to investigate the relationships between exercise capacity and clinical variables, including nutritional indicators, early after HTx.

PATIENTS AND METHODS

Forty-three HTx recipients were studied. The mean age at HTx was 38 ± 14 years, and 86% were male. We assessed the relationships between peak oxygen uptake (VO₂ ) and clinical variables, including plasma B-type natriuretic peptide (BNP), isometric knee extensor muscle strength (KEMS), and nutritional indicators within 1 week of their respective discharges.

RESULTS

Peak VO₂ correlated positively with isometric KEMS (r = .63, P < .0001) and negatively with BNP level (r = -.37, P = .015). Of the nutritional indicators, only cholinesterase levels had a significant relationship with peak VO₂ (r = .34, P = .028), whereas the Geriatric Nutritional Risk Index and the Controlling Nutritional Status scores did not. In multiple linear regression analysis, cholinesterase levels and isometric KEMS were independent predictors of peak VO₂ .

CONCLUSION

Cholinesterase levels predicted exercise capacity early after HTx.

Exercise-based cardiac rehabilitation in heart transplant recipients

BACKGROUND

Heart transplantation is considered to be the gold standard treatment for selected patients with end-stage heart disease when medical therapy has been unable to halt progression of the underlying pathology. Evidence suggests that aerobic exercise training may be effective in reversing the pathophysiological consequences associated with cardiac denervation and prevent immunosuppression-induced adverse effects in heart transplant recipients.

OBJECTIVES

To determine the effectiveness and safety of exercise-based rehabilitation on the mortality, hospital admissions, adverse events, exercise capacity, health-related quality of life, return to work and costs for people after heart transplantation.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library, MEDLINE (Ovid), Embase (Ovid), CINAHL (EBSCO) and Web of Science Core Collection (Thomson Reuters) to June 2016. We also searched two clinical trials registers and handsearched the reference lists of included studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of parallel group, cross-over or cluster design, which compared exercise-based interventions with (i) no exercise control (ii) a different dose of exercise training (e.g. low- versus high-intensity exercise training); or (iii) an active intervention (i.e. education, psychological intervention). The study population comprised adults aged 18 years or over who had received a heart transplant.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened all identified references for inclusion based on pre-specified inclusion criteria. Disagreements were resolved by consensus or by involving a third person. Two review authors extracted outcome data from the included trials and assessed their risk of bias. One review author extracted study characteristics from included studies and a second author checked them against the trial report for accuracy.

MAIN RESULTS

We included 10 RCTs that involved a total of 300 participants whose mean age was 54.4 years. Women accounted for fewer than 25% of all study participants. Nine trials which randomised 284 participants to receive exercise-based rehabilitation (151 participants) or no exercise (133 participants) were included in the main analysis. One cross-over RCT compared high-intensity interval training with continued moderate-intensity training in 16 participants. We reported findings for all trials at their longest follow-up (median 12 weeks).Exercise-based cardiac rehabilitation increased exercise capacity (VO_2peak) compared with no exercise control (MD 2.49 mL/kg/min, 95% CI 1.63 to 3.36; N = 284; studies = 9; moderate quality evidence). There was evidence from one trial that high-intensity interval exercise training was more effective in improving exercise capacity than continuous moderate-intensity exercise (MD 2.30 mL/kg/min, 95% CI 0.59 to 4.01; N = 16; 1 study). Four studies reported health-related quality of life (HRQoL) measured using SF-36, Profile of Quality of Life in the Chronically Ill (PLC) and the World Health Organization Quality Of Life (WHOQoL) - BREF. Due to the variation in HRQoL outcomes and methods of reporting we were unable to meta-analyse results across studies, but there was no evidence of a difference between exercise-based cardiac rehabilitation and control in 18 of 21 HRQoL domains reported, or between high and moderate intensity exercise in any of the 10 HRQoL domains reported. One adverse event was reported by one study.Exercise-based cardiac rehabilitation improves exercise capacity, but exercise was found to have no impact on health-related quality of life in the short-term (median 12 weeks follow-up), in heart transplant recipients whose health is stable.There was no evidence of statistical heterogeneity across trials for exercise capacity and no evidence of small study bias. The overall risk of bias in included studies was judged as low or unclear; more than 50% of included studies were assessed at unclear risk of bias with respect to allocation concealment, blinding of outcome assessors and declaration of conflicts of interest. Evidence quality was assessed as moderate according to GRADE criteria.

AUTHORS' CONCLUSIONS

We found moderate quality evidence suggesting that exercise-based cardiac rehabilitation improves exercise capacity, and that exercise has no impact on health-related quality of life in the short-term (median 12 weeks follow-up), in heart transplant recipients. Cardiac rehabilitation appears to be safe in this population, but long-term follow-up data are incomplete and further good quality and adequately-powered trials are needed to demonstrate the longer-term benefits of exercise on safety and impact on both clinical and patient-related outcomes, such as health-related quality of life, and healthcare costs.

Exercise-based cardiac rehabilitation in heart transplant recipients

BACKGROUND

Heart transplantation is considered to be the gold standard treatment for selected patients with end-stage heart disease when medical therapy has been unable to halt progression of the underlying pathology. Evidence suggests that aerobic exercise training may be effective in reversing the pathophysiological consequences associated with cardiac denervation and prevent immunosuppression-induced adverse effects in heart transplant recipients.

OBJECTIVES

To determine the effectiveness and safety of exercise-based rehabilitation on the mortality, hospital admissions, adverse events, exercise capacity, health-related quality of life, return to work and costs for people after heart transplantation.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library, MEDLINE (Ovid), Embase (Ovid), CINAHL (EBSCO) and Web of Science Core Collection (Thomson Reuters) to June 2016. We also searched two clinical trials registers and handsearched the reference lists of included studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of parallel group, cross-over or cluster design, which compared exercise-based interventions with (i) no exercise control (ii) a different dose of exercise training (e.g. low- versus high-intensity exercise training); or (iii) an active intervention (i.e. education, psychological intervention). The study population comprised adults aged 18 years or over who had received a heart transplant.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened all identified references for inclusion based on pre-specified inclusion criteria. Disagreements were resolved by consensus or by involving a third person. Two review authors extracted outcome data from the included trials and assessed their risk of bias. One review author extracted study characteristics from included studies and a second author checked them against the trial report for accuracy.

MAIN RESULTS

We included 10 RCTs that involved a total of 300 participants whose mean age was 54.4 years. Women accounted for fewer than 25% of all study participants. Nine trials which randomised 284 participants to receive exercise-based rehabilitation (151 participants) or no exercise (133 participants) were included in the main analysis. One cross-over RCT compared high-intensity interval training with continued moderate-intensity training in 16 participants. We reported findings for all trials at their longest follow-up (median 12 weeks).Exercise-based cardiac rehabilitation increased exercise capacity (VO2peak) compared with no exercise control (MD 2.49 mL/kg/min, 95% CI 1.63 to 3.36; N = 284; studies = 9; moderate quality evidence). There was evidence from one trial that high-intensity interval exercise training was more effective in improving exercise capacity than continuous moderate-intensity exercise (MD 2.30 mL/kg/min, 95% CI 0.59 to 4.01; N = 16; 1 study). Four studies reported health-related quality of life (HRQoL) measured using SF-36, Profile of Quality of Life in the Chronically Ill (PLC) and the World Health Organization Quality Of Life (WHOQoL) - BREF. Due to the variation in HRQoL outcomes and methods of reporting we were unable to meta-analyse results across studies, but there was no evidence of a difference between exercise-based cardiac rehabilitation and control in 18 of 21 HRQoL domains reported, or between high and moderate intensity exercise in any of the 10 HRQoL domains reported. One adverse event was reported by one study.Exercise-based cardiac rehabilitation improves exercise capacity, but exercise was found to have no impact on health-related quality of life in the short-term (median 12 weeks follow-up), in heart transplant recipients whose health is stable.There was no evidence of statistical heterogeneity across trials for exercise capacity and no evidence of small study bias. The overall risk of bias in included studies was judged as low or unclear; more than 50% of included studies were assessed at unclear risk of bias with respect to allocation concealment, blinding of outcome assessors and declaration of conflicts of interest. Evidence quality was assessed as moderate according to GRADE criteria.

AUTHORS' CONCLUSIONS

We found moderate quality evidence suggesting that exercise-based cardiac rehabilitation improves exercise capacity, and that exercise has no impact on health-related quality of life in the short-term (median 12 weeks follow-up), in heart transplant recipients. Cardiac rehabilitation appears to be safe in this population, but long-term follow-up data are incomplete and further good quality and adequately-powered trials are needed to demonstrate the longer-term benefits of exercise on safety and impact on both clinical and patient-related outcomes, such as health-related quality of life, and healthcare costs.

Chest Fat Quantification via CT Based on Standardized Anatomy Space in Adult Lung Transplant Candidates

Purpose

Overweight and underweight conditions are considered relative contraindications to lung transplantation due to their association with excess mortality. Yet, recent work suggests that body mass index (BMI) does not accurately reflect adipose tissue mass in adults with advanced lung diseases. Alternative and more accurate measures of adiposity are needed. Chest fat estimation by routine computed tomography (CT) imaging may therefore be important for identifying high-risk lung transplant candidates. In this paper, an approach to chest fat quantification and quality assessment based on a recently formulated concept of standardized anatomic space (SAS) is presented. The goal of the paper is to seek answers to several key questions related to chest fat quantity and quality assessment based on a single slice CT (whether in the chest, abdomen, or thigh) versus a volumetric CT, which have not been addressed in the literature.

Methods

Unenhanced chest CT image data sets from 40 adult lung transplant candidates (age 58 ± 12 yrs and BMI 26.4 ± 4.3 kg/m²), 16 with chronic obstructive pulmonary disease (COPD), 16 with idiopathic pulmonary fibrosis (IPF), and the remainder with other conditions were analyzed together with a single slice acquired for each patient at the L5 vertebral level and mid-thigh level. The thoracic body region and the interface between subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) in the chest were consistently defined in all patients and delineated using Live Wire tools. The SAT and VAT components of chest were then segmented guided by this interface. The SAS approach was used to identify the corresponding anatomic slices in each chest CT study, and SAT and VAT areas in each slice as well as their whole volumes were quantified. Similarly, the SAT and VAT components were segmented in the abdomen and thigh slices. Key parameters of the attenuation (Hounsfield unit (HU) distributions) were determined from each chest slice and from the whole chest volume separately for SAT and VAT components. The same parameters were also computed from the single abdominal and thigh slices. The ability of the slice at each anatomic location in the chest (and abdomen and thigh) to act as a marker of the measures derived from the whole chest volume was assessed via Pearson correlation coefficient (PCC) analysis.

Results

The SAS approach correctly identified slice locations in different subjects in terms of vertebral levels. PCC between chest fat volume and chest slice fat area was maximal at the T8 level for SAT (0.97) and at the T7 level for VAT (0.86), and was modest between chest fat volume and abdominal slice fat area for SAT and VAT (0.73 and 0.75, respectively). However, correlation was weak for chest fat volume and thigh slice fat area for SAT and VAT (0.52 and 0.37, respectively), and for chest fat volume for SAT and VAT and BMI (0.65 and 0.28, respectively). These same single slice locations with maximal PCC were found for SAT and VAT within both COPD and IPF groups. Most of the attenuation properties derived from the whole chest volume and single best chest slice for VAT (but not for SAT) were significantly different between COPD and IPF groups.

Conclusions

This study demonstrates a new way of optimally selecting slices whose measurements may be used as markers of similar measurements made on the whole chest volume. The results suggest that one or two slices imaged at T7 and T8 vertebral levels may be enough to estimate reliably the total SAT and VAT components of chest fat and the quality of chest fat as determined by attenuation distributions in the entire chest volume.

Design and rationale of the HITTS randomized controlled trial: Effect of High-intensity Interval Training in de novo Heart Transplant Recipients in Scandinavia

There is no consensus on how, when, and at what intensity exercise should be performed and organized after heart transplantation (HTx). Most rehabilitation programs are conducted in HTx centers, which might be impractical and costly. We have recently shown that high-intensity interval training (HIT) is safe, well tolerated, and efficacious in maintenance HTx recipients, but there are no studies among de novo patients, and whether HIT is feasible and superior to moderate training in HTx recipients is unclear. A total of 120 clinically stable HTx recipients older than 18 years will be recruited from 3 Scandinavian HTx centers. Participants are randomized to HIT or moderate training, shortly after surgery. All exercises are supervised in the patients' local communities. Testing at baseline and follow-up includes the following: VO2peak (primary end point), muscle strength, body composition, quality of life, myocardial performance, endothelial function, biomarkers, and progression of cardiac allograft vasculopathy. A subgroup (n = 90) will also be tested at 3-year follow-up to assess long-term effects of exercise. So far, the HIT intervention is well tolerated, without any serious adverse events. We aim to test whether decentralized HIT is feasible, safe, and superior to moderate training, and whether it will lead to significant improvement in exercise capacity and less long-term complications.

Maximal cardiac output in athletes: influence of age

BACKGROUND

The decline in maximal oxygen consumption (VO2max) with age seems to be exacerbated in endurance-trained athletes (EA) relative to untrained healthy subjects. Whether maximal cardiac output (Qmax) parallels this group-specific decline with age remains uncertain. Therefore, we sought to systematically review the literature and determine whether Qmax is similarly enhanced in EA across all ages relative to age-matched untrained counterparts.

DESIGN AND METHODS

We conducted a systematic search of MEDLINE, Cochrane and Web of Science from their inceptions until June 2014 for articles evaluating Qmax in athletes. A meta-analysis was performed to determine the standardized mean difference (SMD) in Qmax between EA and age-matched untrained healthy subjects. Included studies had to (i) comprise EA and control groups matched for body size or (ii) present Qmax values normalized for body size. Subgroup and meta-regression analyses were used to study the influence of age and potential moderating factors.

RESULTS

Eighteen studies were selected after systematic review, comprising 268 EA and 232 age-matched untrained subjects. Nine studies involved young EA (mean age ≤40 years) while nine studies involved master EA (mean age >55 years). After data pooling, young and master EA groups showed higher Qmax compared with control groups (SMD = 1.49 and SMD = 1.68, respectively; both p < 0.0001). The SMD in Qmax between EA and control groups was similar in studies in young EA compared with studies in master EA (p = 0.61). Moreover, the SMD in VO2max between EA and control groups did not differ in studies in young EA compared with studies in master EA (p = 0.37). In meta-regression analyses, the difference in percentage of body fat between EA and control groups was inversely associated with the SMD in Qmax (B = - 0.17, p = 0.01) and the SMD in VO2max (B = -0.20, p = 0.01). Mean age was not associated with the SMD in Qmax (B = -0.001, P = 0.90) nor with the SMD in VO2max (B = 0.01, P = 0.58).

CONCLUSIONS

Based on current published studies, the enhanced Qmax observed in EA compared with untrained healthy subjects matched for body size is not affected by age but may be related, at least in part, to the improved body composition of EA.

Exercise after heart transplantation: An overview

While life expectancy is greatly improved after a heart transplant, survival is still limited, and compared to the general population, the exercise capacity and health-related quality of life of heart transplant recipients are reduced. Increased exercise capacity is associated with a better prognosis. However, although several studies have documented positive effects of exercise after heart transplantation (HTx), little is known about the type, frequency and intensity of exercise that provides the greatest health benefits. Moreover, the long-term effects of exercise on co-morbidities and survival are also unclear. Exercise restrictions apply to patients with a denervated heart, and for decades, it was believed that the transplanted heart remained denervated. This has since been largely disproved, but despite the new knowledge, the exercise restrictions have largely remained, and up-to-date guidelines on exercise prescription after HTx do not exist. High-intensity, interval based aerobic exercise has repeatedly been documented to have superior positive effects and health benefits compared to moderate exercise. This applies to both healthy subjects as well as in several patient groups, such as patients with metabolic syndrome, coronary artery disease or heart failure. However, whether the effects of this type of exercise are also applicable to heart transplant populations has not yet been fully established. The purpose of this article is to give an overview of the current knowledge about the exercise capacity and effect of exercise among heart transplant recipients and to discuss future exercise strategies.

Effect of high-intensity interval training on progression of cardiac allograft vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a progressive form of atherosclerosis occurring in heart transplant (HTx) recipients, leading to increased morbidity and mortality. Given the atheroprotective effect of exercise on traditional atherosclerosis, we hypothesized that high-intensity interval training (HIIT) would reduce the progression of CAV among HTx recipients.

METHODS

Forty-three cardiac allograft recipients (mean ± SD age 51 ± 16 years; 67% men; time post-HTx 4.0 ± 2.2 years), all clinically stable and >18 years old, were randomized to either a HIIT group or control group (standard care) for 1 year. The effect of training on CAV progression was assessed by intravascular ultrasound (IVUS).

RESULTS

IVUS analysis revealed a significantly smaller mean increase [95% CI] in atheroma volume (PAV) of 0.9% [95% CI -;0.3% to 1.9%] in the HIIT group as compared with the control group, 2.5% [1.6% to 3.5%] (p = 0.021). Similarly, the mean increase in total atheroma volume (TAV) was 0.3 [0.0 to 0.6] mm(3)/mm in the HIT group vs 1.1 [0.6 to 1.7] mm(3)/mm in the control group (p = 0.020), and mean increase in maximal intimal thickness (MIT) was 0.02-0.01 to 0.04] mm in the HIIT group vs 0.05 [0.03 to 0.08] mm in the control group (p = 0.054). Qualitative plaque progression (virtual histology parameters) and inflammatory activity (biomarkers) were similar between the 2 groups during the study period.

CONCLUSIONS

HIIT among maintenance HTx recipients resulted in a significantly impaired rate of CAV progression. Future larger studies should address whether exercise rehabilitation strategies should be included in CAV management protocols.

High-intensity interval training improves peak oxygen uptake and muscular exercise capacity in heart transplant recipients

Heart transplant (HTx) recipients usually have reduced exercise capacity with reported VO(2peak) levels of 50-70% predicted value. Our hypothesis was that high-intensity interval training (HIIT) is an applicable and safe form of exercise in HTx recipients and that it would markedly improve VO(2peak.) Secondarily, we wanted to evaluate central and peripheral mechanisms behind a potential VO(2peak) increase. Forty-eight clinically stable HTx recipients >18 years old and 1-8 years after HTx underwent maximal exercise testing on a treadmill and were randomized to either exercise group (a 1-year HIIT-program) or control group (usual care). The mean ± SD age was 51 ± 16 years, 71% were male and time from HTx was 4.1 ± 2.2 years. The mean VO(2peak) difference between groups at follow-up was 3.6 [2.0, 5.2] mL/kg/min (p < 0.001). The exercise group had 89.0 ± 17.5% of predicted VO(2peak) versus 82.5 ± 20.0 in the control group (p < 0.001). There were no changes in cardiac function measured by echocardiography. We have demonstrated that a long-term, partly supervised and community-based HIIT-program is an applicable, effective and safe way to improve VO(2peak) , muscular exercise capacity and general health in HTx recipients. The results indicate that HIIT should be more frequently used among stable HTx recipients in the future.