It is estimated that each of the aforementioned centers receives ~60 SCD per year, but only around one fourth of them will fulfill the inclusion criteria, namely VF as first documented rhythm and ECG tracing availability. Considering the inclusion of 2 more centers (currently undertaking protocol evaluation), the incidence of annual new cases per hospital and retrospective cases from previous years, the sample size will be achieved in a time frame of 30 months. The latter includes the follow-up period for the last group of patients who will be enrolled in the study. As of the writing of this manuscript, the starting center (Hospital Clínico San Carlos) has already evaluated 60 patients, of who 21 met the inclusion criteria and are enrolled in the trial.