This study was supported by two research grants, one from the Pediatric and Congenital Electrophysiology Society (PACES) and another from the American Academy of Pediatrics (AAP) Children's Heart Foundation (CHF). Justin D. Opfermann and Charles I. Berul are co-founders of PeriCor, LLC. Charles I. Berul is a consultant for Medtronic. Justin D. Opfermann, Paige N. Mass, Dr. Charles I. Berul, and Dr. Rohan N. Kumthekar are also members of and hold Shares of Stock Options in PeriCor, LLC. The results of the study discussed in this publication could affect the value of PeriCor, LLC. This arrangement has been reviewed and approved by the Johns Hopkins University in accordance with its conflict-of-interest policies.