The goal of this observational study is to establish the protocol of systemic analysis of the causes of non-traumatic cardiac arrest in young patients. The main questions it aims to answer are: * Whether the protocolized classification of cardiac arrest minimizes the proportion of unknown causes and mis-classification in young cardiac arrest patients? * Whether the incorporation of genetic tests in the identification protocol of arrest cause helps the recognition of sudden arrhythmic death syndrome in young cardiac arrest patients? Participants will be asked to received serial examinations including genetic analysis to explore the cause of cardiac arrest.