Three-month follow-up visit and crossover procedures: Patients will be scheduled to return to the CRC 3 months after study entry. Once a visit is confirmed, each patient will be asked to stop his or her current AAD 5 half-lives (approximately 60 hours) prior to arrival to the CRC. Patients initially taking flecainide will also stop their AV nodal blocker (atenolol or diltiazem) at this time. Patients will then present to the CRC and undergo initiation of the alternative drug using the same procedures that were used at the baseline study visit, with the exception of the ICM insertion. A full interrogation of the ICM will be performed. A pill count will be performed to further assess compliance. Patients crossing over to flecainide will be discharged from the CRC after a 2 hour 12-lead ECG is obtained and interpreted as normal. Patients initiating sotalol will remain in the CRC for loading and continuous telemetric monitoring. All patients will be scheduled for a brief follow-up visit in the CRC one week after crossover to assess for medication compliance and tolerance and for final titration of flecainide.