Evaluation of Exercise Testing and Physical Activity in Children and Adolescents Living With Inherited Arrhythmias

The goal of this observational study is to evaluate exercise testing and daily physical activity in children and adolescents who are diagnosed with an inherited arrhythmia. The main question it aims to answer is: Does maximum heart rate during controlled exercise tolerance testing accurately reflect maximum heart rate and peak exercise levels during free living daily physical activity in children and adolescents diagnosed with an inherited arrhythmia? Participants will: * Complete routine exercise tolerance testing * Record daily physical activity and exercise over two weeks, while wearing an activity and heart rate monitor and digit diary. * Complete a physical activity questionnaire at the end of two weeks.

Exercise tolerance testing (ETT) using an exercise treadmill is a tool used to assess children's physical response to stress, which is thought to accurately reflect normal physiology during normal daily activities and can be used to: * Evaluate heart rhythm and symptoms occurring during exercise. * Evaluate children with a family history of sudden death and inherited heart conditions. * Assess the response of medications prescribed to control heart rhythm. The maximum heart rate achieved during ETT is used to estimate the effect of daily medications and to guide exercise prescription. Originally designed to assess adult heart disease patients, ETTs were not intended for use in children. To accommodate the needs of children, shorter ETT protocols have been developed which increase the speed and/or incline of the treadmill quickly. Despite this, many children rarely complete the full ETT protocol as they grow tired or develop other symptoms, which leads to them stopping exercise early, resulting in variable lengths of testing. Children naturally increase exercise effort during day-to-day free-living physical activity (PA). Free-living PA is therefore thought to show a more accurate representation of the maximum heart rate (HR) children can achieve. Presently there is no strong evidence base to determine what children with an Inherited Arrhythmia (IA) (a genetically inherited heart condition which causes abnormalities in the heart rhythm) are doing in terms of daily free-living PA and exercise. The current recommendations used to prescribe exercise for this patient group are based on expert opinion and are not child specific. The study I propose supports the development of a greater evidence base to guide future exercise prescription and better tailored medications. The study aims to: * To compare the maximum HR achieved during controlled ETT with the maximum HR achieved during daily free-living PA and exercise, to see if these are different. * To assess three different exercise testing protocols for children, and identify if one is better than the others at estimating maximum heart rate compared with free-living PA. * To investigate the actual versus reported PA children engage in using a questionnaire and digital PA diary. To achieve these aims, the study will recruit children (aged 6-16 years) diagnosed with an IA and who are able to run on an exercise treadmill, plus a healthy control group (unaffected siblings, or children undergoing screening). A clinical ETT will be performed as part of routine care. Each participant will be given a wearable PA monitoring device to monitor free-living PA over two-weeks. The device will record parameters such as electrocardiogram, HR, and step count. PA will also be recorded digitally to capture type and length of activity they engage in, and estimated intensity. At the end of the two-weeks, participants will complete a questionnaire about their PA which will be compared with the data obtained during the monitoring period. Parents will be invited to support younger children with questionnaire and digital recording completion. A study lay advisory group will be established including children and their parents affected by an IA. They will advise on study design and development of all patient-facing information throughout the study. The results of the study will be discussed with lay advisory groups who will advise on the best ways to share results with the wider public but will include publication in high quality Open Access journals and dissemination at relevant national and international conferences. Invitations will also be provided to the voluntary support groups involved in the early planning phases to publish the results on their websites