Prevention of Post-Operative Cardiac Arrhythmias

Aim 1: Primary Prevention of Post-operative Cardiac Arrhythmias 1. To evaluate the efficacy of dexmedetomidine vs. the combination of Magnesium Sulfate and dexmedetomidine for the prevention of post-operative cardiac arrhythmias in children and young adults undergoing open heart surgical repair for congenital or acquired heart disease using cardiopulmonary bypass. Dexmedetomidine is currently being administered to almost all patients after coming off cardiopulmonary bypass and in the CICU. For this aim, the investigator will be comparing dexmedetomidine administered alone or in combination with Magnesium Sulfate. 2. To evaluate medication safety based on the frequency of Serious Adverse Events (SAEs) and Adverse Events (AEs) Aim 2: Secondary treatment of those Patients that develop a clinically significant arrhythmia despite having received either Dexmedetomidine alone or Magnesium Sulfate with Dexmedetomidine at the time of cardiac surgery 1. To evaluate the efficacy of intravenous (IV) Amiodarone vs. IV Procainamide for the control of postoperative cardiac arrhythmias developing after the failure of Stage 1, Preventative Trial. IV amiodarone and IV procainamide are standardly used treatment agents for the treatment of postoperative cardiac arrhythmias in this setting. The investigator will be assessing the comparative effectiveness of these agents in controlling post-operative cardiac arrhythmias. 2. To evaluate antiarrhythmic medication safety based on the frequency of SAEs and AEs