Heart transplantation is the long-term treatment for children and adults with advanced heart failure. Post-transplant outcomes have improved over time, such that 50% of pediatric heart transplant recipients (HTR) remain alive with a need for re-transplantation 17-years following the initial transplant. With improved short- and medium-term outcomes, focus has shifted towards optimizing long-term survival and reducing transplant-associated morbidities. This includes strategies aimed at optimizing cardiorespiratory fitness and physical activity levels.

Pediatric and adult HTRs have reduced exercise capacity compared with the general population. Previous groups have shown gradual improvements in heart rate response to exercise and exercise capacity in pediatric HTRs. However, after an initial improvement, exercise capacity appears to plateau, or even decline in pediatric HTRs, and remains sub-optimal compared with the general population.

Most exercise interventions in HTRs to date have focused on moderate-intensity continuous exercise (MICE), with some resistance components incorporated. More recently, high-intensity interval training (HIIT), consisting of short, intense bursts of exercise with rest periods, has been explored in the adult HTR population, with findings to date suggesting that it may yield greater improvements in cardiorespiratory fitness compared with MICE. Exercise interventions, particularly HIIT interventions, have consistently shown clinically important improvements in exercise capacity in adult HTRs that are linked with improved long-term post-transplant outcomes and well-being. Unfortunately, trials of exercise interventions in pediatric HTRs remain lacking. This study team is proposing an assessment of the feasibility of a home-based HIIT exercise program using a novel telemedicine-enable video game linked customizable cycle ergometer (MedBIKE™).

Purpose: To determine the feasibility of MedBIKE™ in a 12-week home-based high intensity interval training program in pediatric heart transplant recipients (HTRs).

Hypothesis: The MedBIKE™ intervention will be feasible, with adequate enrolment of eligible participants (>60%), high session compliance (>80%), and low-drop out rate (~10%), with no adverse events directly related to the intervention. The investigators further hypothesize that the MedBIKE™ HIIT intervention will result in immediate and sustained improvements in exercise capacity, physical activity, self-efficacy towards physical activity, and HRQoL.

Justification: Clinical trials of exercise interventions in pediatric HTRs remains significantly lacking. This lack of literature to date has been identified as a significant knowledge gap in the Canadian Society of Transplantation/CAN-RESTORE recent joint statement. While the findings to date indicate that exercise interventions in pediatric HTRs may show improvements in exercise capacity, numerous knowledge gaps remain. For example, despite promising findings in adult HTRs, HIIT has not yet been studied in pediatric HTRs. Moreover, the effect of exercise interventions on physical activity, HRQoL, and self-efficacy towards physical activity have not been well studied. It is important to evaluate whether a supervised exercise intervention at near-maximal intensity can promote improvements in physical activity self-efficacy that may in turn yield sustained improvements in physical activity. One of the limiting factors for regular participation in post-transplant exercise programs is the necessary time commitment that is intensified in a program with demographics such as ours in Western Canada with many post-transplant children living far from the transplant center and with limited access to exercise facilities. A supervised home-based training program could optimize the time-efficiency and accommodate the patient's routine schedules. Thus, the investigators are proposing an assessment of the feasibility of a home-based HIIT exercise program using a novel telemedicine-enabled video game-linked customizable cycle ergometer (MedBIKE™).

Objectives: (Primary) Evaluate the feasibility of a 12-week, home-based HIIT MedBIKE™ intervention in pediatric HTRs. (Secondary) Evaluate the impact of the MedBIKE™ HIIT intervention on 1) exercise capacity; 2) physical activity; 3) self-efficacy towards physical activity; 4) HRQoL and 5) sustained changes in all secondary outcomes at 6- and 12-months post-intervention.

Research Method: Single-center, randomized crossover feasibility trial with a multi-method approach. Potential participants and families will be approached first by a clinical team member. Participants and parents expressing interest will meet with a research coordinator who, along with one of the investigators and the clinical team will screen for eligibility. Written consent and assent (if applicable) will be obtained from participants who are deemed eligible.

Following recruitment, participants will be administered the PedsQL and CSAPPA questionnaires, an accelerometer will be provided for seven days, and a baseline CPET will be performed or scheduled to occur following completion of the accelerometer assessment. Participants will then be randomized via a 1:1 allocation ratio with permuted blocks of randomly varied sizes either to the immediate MedBIKE™ arm or the immediate control arm (usual care) for 12-weeks, followed by a repeat assessment. Participants in the control arm will then cross-over and complete the 12-week MedBIKE™ HIIT program, followed by a repeat assessment at the completion of the intervention. All post-intervention assessments will occur 3-7 days post-MedBIKE™ intervention (to allow adequate recovery) and accelerometers will be programmed to commence counts 24 hours post-assessment to avoid bias from fatigue from the CPET. Participants will then return for final assessments at 6- and 12-months post-MedBIKE™ intervention. Whenever possible, follow-up assessments will be coordinated with clinical appointments (pediatric HTRs are typically clinically assessed every 3-4 months or more frequently).

The MedBIKE™ program is a first-person interactive videogame in which the participant is 'biking' around a safari collecting animals and will enter a wormhole when completing the high-intensity exercise portion. The participant and clinician applications are Windows WPF applications that run on windows 10 PCs. The participant application also includes a companion app that runs on an Android table. The MedBIKE™ service application is a platform-independent Python application that is run on a a secure Ubuntu Linux instance operated by the University of Alberta's Faculty of Medicine and Dentistry IT department.

A follow-up assessment, identical to that of the baseline (questionnaires, CPET, interviews and a 7-day week wear of an accelerometer) will occur 3-14 days post-intervention. These assessments will be repeated at 6- and 12-months post-intervention.

Plan for Data Analysis: The WHCRI biostatistics group will provide statistical and data analysis support. Continuous data will be summarized as median with first and third quartiles and changes in pre- and post-intervention measures will be evaluated using the Mann-Whitney test. Categorical data will be presented by absolute and relative frequencies (n and %). All statistical analyses will be performed by SAS 9.4 or later (SAS Institute Inc., Cary, NC, USA).

Inclusion Criteria:

• Pediatric heart transplant recipients, at least 6-months post heart transplantation
• Aged 10-18 years

Exclusion Criteria:

• Non-English speaking (thus limiting communication during the MedBIKE™ sessions)
• Home environment cannot accommodate the MedBIKE™ system (for example, space limitations)
• History of multiorgan transplant
• Adult unavailable to supervise the home-based exercise sessions
• Episode of clinical antibody- or cellular-mediated rejection within 3-months of the baseline assessment
• Previous involvement in a cardiac rehabilitation or exercise intervention program
• Primary cardiologist has exercise restricted the participant or counsels against participation
• Previous exercise stress test demonstrating sustained arrhythmias, ST segment elevation or depression greater than 3mm, an inappropriate rise in blood pressure (BP) (<20 mmHg) or a systolic BP >200 mmHg, or symptoms of chest pain or syncope
• Resting arterial saturation <85% or oxygen requirements
• Moderate ventricular systolic dysfunction (or worse) at the most recent echocardiogram
• History of chest pain on exertion
• Unrepaired/unpalliated CHD
• Arrhythmias in the last year (including supraventricular tachycardia, ventricular tachycardia, atrioventricular block (Mobitz II or worse))
• New York Heart Association class II or worse symptoms
• Active medical inter-current illness limiting ability to participate
• Cognitive impairment limiting the communication needed for the HIIT program
• Extracardiac or congenital abnormality limiting the participant's functional ability to exercise

Individual participant data will not be shared with other researchers. All data will be de-identified prior to analysis and publication.