• Syncopenon
  Traumatic and reversible loss of consciousness, and was considered of arrhythmia origin in the absence of prodrome or triggering circumstances.
  
  
• SCD
  Is an abrupt, unexpected death due to cardiac causes that occurs in a short time period (generally within 1 hour of symptoms onset)
  
  
• SND
  Assessed both clinically and invasively during the electrophysiological study. Clinically, sinus node dysfunction will be evaluated by 12-lead electrocardiograms, Holter monitoring, and exercise tests, and defined as inappropriate sinus bradycardia according to age and activity level, sinus pause/arrest > 2.5 s, and chronotropic incompetence.
  
  
• Chronotropic incompetence
  Is defined as failure to achieve 85% of the age-predicted maximum heart rate during the exercise test.
  
  
• Conduction abnormalities
  Include PR and QRS prolongation, and were evaluated in 12 lead electrocardiograms. Prolongation of PR, QRS, and QT intervals were defined as those values above the 98 percentile for age.