Background-The ability to identify and ablate different arrhythmia mechanisms after the total cavopulmonary connection has not been studied in detail. Methods and Results-After obtaining Institutional Review Board approval according to institutional guidelines, consecutive patients after a total cavopulmonary connection undergoing electrophysiology study over a 6-year period were included (2006)(2007)(2008)(2009)(2010)(2011)(2012). Arrhythmia mechanism was determined, and the procedural outcome

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... was defined as complete, partial success, or failure. A 12-point arrhythmia severity score was calculated for each patient at baseline and on follow-up. Fifty-seven procedures were performed on 52 patients (18.4±11.8 years; 53.0±27.2 kg). Access to the pulmonary venous atrium was necessary in 33 procedures, via fenestration (16) or transbaffle puncture (17) , and in 2 cases, an additional retrograde approach was used. In total, 80 arrhythmias were identified in 47 cases: macroreentrant (n=25) or focal atrial tachycardia (n=8), atrioventricular nodal reentry tachycardia (n=13), reentry via an accessory pathway (n=4) or via twin atrioventricular nodes (n=4), ventricular tachycardia (n=5), and undefined atrial tachycardia (n=21). Procedural outcome in 32 patients who underwent ablation was complete success (n=25), partial success (n=3), failure (n=3), or empirical ablation (n=1). After successful ablation, there was a significant decrease in arrhythmia score over 18.2 (4-32) months follow-up, with a sustained trend even in the face of arrhythmia recurrence (50%). Conclusions-Arrhythmia mechanism post total cavopulmonary connection is highly varied, encompassing simple and more complex substrates, documentation of which facilitates a strategic approach to invasive arrhythmia management. Despite the anatomic limitations, successful and clinically meaningful ablation is possible. (Circ Arrhythm Electrophysiol. 2015;8:318-325.