Candidates must meet all of the inclusion criteria required for inclusion in one of the two groups (summarized in Table 2). All of the patients need to have a positive P wave of > 0.5 mm in lead 2. Patients must have had ≥ 1 syncope during the 6 months preceding enrollment and ≥ 2 syncopes in their lifetime except if the last syncope was complicated by an injury or an accident, in which case further waiting for CardNM may be less desirable. Patients < 18 years must have least 3 syncopes with an interval exceeding 1 month unless 1 syncope was complicated by an injury or an accident.