Abstract Body (Do not enter title and authors here): Introduction:
Patients with Fontan circulation are at an increased risk of sinus node dysfunction and atrial tachyarrhythmias. These are associated with significant morbidity and mortality, and management constitutes a significant clinical challenge.

Case Description:
A 44-year-old male with right ventricular hypoplasia, tricuspid and pulmonic valve atresia and a ventricular septal defect, corrected with a modified Blalock-Taussig Shunt, bidirectional Glenn Shunt and atrio-pulmonary Fontan, was admitted with a supraventricular tachycardia (SVT) and heart failure. His electrocardiogram showed a narrow complex mid-RP tachycardia consistent with atypical atrial flutter or atrial tachycardia. His echocardiogram showed an LVEF of 21%. He was started on a beta-blocker and loaded with dofetilide, resulting in bradycardia, QT interval prolongation and Torsades de Pointes. Amiodarone was substituted, but he had incessant SVTs. He was taken for an electrophysiology study and radiofrequency ablation of a right-sided re-entrant flutter around an area of block in the anterior septum. Four additional unstable atrial tachycardias were induced but not ablated. He was discharged, then readmitted within hours for SVT. Due to insurance status, the patient was not a candidate for transplant or Fontan revision. To enable treatment with a beta-blocker, an Abbott leadless atrial pacemaker (AVEIR AR) was implanted in the high lateral Fontan, in an area of normal voltage (Figure 1). Post-implant interrogation showed stable device parameters (capture 0.25 V @ 0.4 ms, sensing 7.6 mV, impedance: 380 Ω).

Conclusions:
This is the first case of an AVEIR AR implanted within an atrio-pulmonary Fontan circulation. Access to atriopulmonary Fontan circulation for endovascular device therapy is feasible, but requires careful pre-procedural planning to ensure vascular patency, and anatomic and physiologic feasibility. Leadless pacing mitigates complications from endocardial and epicardial pacing systems, but long-term safety and efficacy are unknown.