Subcutaneous Implantable Cardioverter-defibrillator (S-ICD) Eligibility Over Time in Arrhythmogenic Cardiomyopathy

The goal of this observational study is to learn whether adults with arrhythmogenic cardiomyopathy, an inherited heart muscle disease that can cause dangerous heart rhythms, remain eligible for a subcutaneous implantable cardioverter-defibrillator (S-ICD) over time. An S-ICD is a device placed under the skin, outside the heart, that can stop life-threatening heart rhythms with an electric shock. Before an S-ICD is implanted, a screening test checks whether the heart's electrical signals, recorded from the skin of the chest, are suitable for the device to work correctly. Because arrhythmogenic cardiomyopathy is a progressive disease, these signals may change over time, and a patient who passes the screening today may not pass it later. The main questions it aims to answer are: * Does S-ICD eligibility remain stable over 18 months in patients with arrhythmogenic cardiomyopathy? * Are changes in eligibility related to changes in the electrocardiogram during follow-up? Researchers will compare patients with arrhythmogenic cardiomyopathy with patients with Brugada syndrome, a condition in which the S-ICD is commonly used, and with people without structural heart disease. Participants will: * Undergo S-ICD screening using the manufacturer's screening algorithm, with electrodes placed on the chest skin, at the start of the study and again at 6, 12 and 18 months * Continue their usual medical care No device will be implanted as part of this study. Any decision to implant a defibrillator will be made by each patient's care team, independently of the study.