Percutaneous Epicardial Ablation of Atrial Fibrillation.

The observations afforded by epicardial mapping have not only increased the appreciation of distinct epicardial structures in the left atrium but also underscore the need to address the substrate transmurally. Although epicardial access and ablation have attendant risks, comparative studies with hybrid surgical approaches are lacking. In the search to find unifying mechanisms of atrial fibrillation, a conceptual shift that emphasizes the substrate in 3 dimensions, with the epicardium distinct from the endocardium, holds promise for future investigation and evolving therapeutic tools.