CardioNerds (Amit Goyal and Daniel Ambider) ACHD series co-chair Dr. Daniel Clark (Vanderbilt University), cardiology FIT lead Dr. Stephanie Fuentes (Houston Methodist Hospital), and Dr. Frank Fish, a Pediatric Electrophysiologist and the Director of the Pediatric Electrophysiology (EP) Lab at Monroe Carrell Jr Children’s Hospital at Vanderbilt University. He is a board certified Adult Congenital Heart Disease (ACHD) physician and has a wealth of experience performing EP procedures in adults living with congenital heart disease. Audio editing was performed by student Dr. Shivani Reddy. In this episode, we discuss key concepts and management of electrophysiologic issues that we can encounter when caring for adults with congenital heart disease.  Arrythmias in adults with congenital heart disease can be intrinsic due to the defect itself or as a consequence of the interventions that they have undergone to palliate and/or repair these defects. The complex anatomy of these patients and the years of pressure and volume load make them not only exquisitely hemodynamically sensitive to arrhythmias (that may otherwise not be of much consequence to the general population) but they also make interventions (catheter ablation or device implant) complex. We therefore embark in a case-based discussion of patients with ACHD (Fontan circulation, Ebstein’s anomaly and Tetralogy of Fallot) in an effort to highlight the presentation of arrythmias and the management strategy in this very important group of patients. The CardioNerds Adult Congenital Heart Disease (ACHD) series provides a comprehensive curriculum to dive deep into the labyrinthine world of congenital heart disease with the aim of empowering every CardioNerd to help improve the lives of people living with congenital heart disease. This series is multi-institutional collaborative project made possible by contributions of stellar fellow leads and expert faculty from several programs, led by series co-chairs, Dr. Josh Saef, Dr. Agnes Koczo, and Dr. Dan Clark. The CardioNerds Adult Congenital Heart Disease Series is developed in collaboration with the Adult Congenital Heart Association, The CHiP Network, and Heart University. See more CardioNerds Adult Congenital Heart Disease PageCardioNerds Episode PageCardioNerds AcademyCardionerds Healy Honor Roll CardioNerds Journal ClubSubscribe to The Heartbeat Newsletter!Check out CardioNerds SWAG!Become a CardioNerds Patron! Pearls - Electrophysiology in ACHD Patients with Fontan circulation have a high risk of developing atrial (and ventricular) arrhythmias and they are highly sensitive to the hemodynamic consequences that these arrythmias ensue.  The goal of therapy then should be to achieve sinus or atrial paced rhythm. Rate control should NOT the goal. Patients with Ebstein’s anomaly have high arrhythmic potential. They can have multiple accessory pathways (especially right sided) which can in turn be associated with sudden cardiac death. We should have low threshold for EPS +/- catheter ablation in patients with WPW pattern. Patients with Tetralogy of Fallot have a unique risk for SCD that warrant ICD implant apart from the standard criteria (LVEF <=35% and NYHA II-III symptoms). This involves the pump (RV dilation/dysfunction), electricity (QRSd>180 ms) and surgical repair approach. Patient’s anatomy is the major consideration when implanting devices (PPM/ICD). We ought to assess for residual intracardiac shunt at the atrial level and consider closing if feasible prior to placing a device. CRT has merit in systemic LV but less so in systemic RV. Notes- Electrophysiology in ACHD What should we know about atrial arrhythmias in a Fontan patient? Intraatrial re-entrant tachycardia (IART) is slower than typical atrial flutter with atrial rates generally