Diagnosis and management of very rare primary arrhythmia syndromes in children and adults: a Clinical Consensus Statement of the European Heart Rhythm Association of the ESC and the Association of Cardiovascular Nursing & Allied Professions of the ESC, endorsed by the Association for European Paediatric and Congenital Cardiology.

Very rare and ultra-rare primary inherited arrhythmia syndromes (IAS) represent a heterogeneous group of disorders associated with a significant risk of sudden cardiac death, often manifesting from foetal life to early adulthood. Current guidelines primarily address more common IAS and provide limited, non-specific recommendations for these rare entities, particularly in paediatric populations. This European Heart Rhythm Association Clinical Consensus Statement, developed in collaboration with the Association of Cardiovascular Nursing and Allied Professions and endorsed by the Association for European Paediatric and Congenital Cardiology, integrates available evidence with expert opinion. Recommendations were formulated through structured discussion and voting, following ESC consensus methodology, with a focus on clinically actionable gene-disease associations. The document provides a comprehensive framework for the diagnosis and management of very rare IAS, including calmodulinopathies, Andersen-Tawil syndrome, Timothy syndrome, TRDN-related disease, calcium release deficiency syndrome, and other atypical channelopathies. It highlights age-specific clinical presentations, the importance of genetic testing, and tailored therapeutic strategies, including pharmacological treatments, left cardiac sympathetic denervation, and selective use of implantable cardioverter-defibrillators. Special attention is given to paediatric considerations, foetal diagnosis, and the role of multidisciplinary care. The document also addresses arrhythmic risk in metabolic and cardiomyopathic conditions, as well as the importance of molecular autopsy and family screening in sudden unexplained death. This consensus document fills a critical gap by providing expert-driven, pragmatic guidance for the management of very rare IAS across the lifespan. It underscores the need for specialized care, international collaboration, and prospective registries to improve evidence generation, risk stratification, and patient outcomes in this vulnerable population.