Abstract
To elucidate the substrate of longstanding AF (CAF), we performed high density epicardial mapping in 24 patients undergoing mitral valve surgery. We failed to find any epicardial circuits or rotors. Instead, the substrate of AF was characterized by a high degree of longitudinal dissociation between muscle bundles and numerous “focal” fibrillation waves originating in the entire atrial wall (right and left). In patients with CAF, the total length of intra-atrial block was more than 6-fold higher than during acutely induced AF. Due to electrical dissociation of neighboring muscle bundles, the fibrillation waves had become very narrow and numerous. During CAF the incidence of “focal” fibrillation waves was almost 4-fold higher than during acute AF. However, in the far majority (90.5%) they occurred as single events. Only 0.8% of “focal” activation waves were repetitive (>3 in succession). Unipolar electrograms recorded at the site of origin of “focal” fibrillation waves exhibited small but clear R-waves. These observations support the notion that these so-called “focal” fibrillation waves originate from endo-epicardial breakthrough rather than from a focal mechanism. Conclusions: Due to longitudinal and endo-epicardial dissociation, the atria are transformed into a double layer of electrically dissociated muscle bundles. AF is maintained by multiple reciprocal endo-epicardial excitations (ping-pong). This “double-layer” hypothesis offers an adequate explanation for the high persistence of AF in patients with structural heart disease.
