title: Loss of continuity in the thin epicardial layer because of endomysial fibrosis increases the complexity of atrial fibrillatory conduction.
abstract: BACKGROUND
  The transition from persistent to permanent atrial fibrillation (AF) is associated with increased complexity of fibrillatory conduction. We have investigated the spatial distribution of fibrillation waves and structural alterations in the atrial free walls in a goat model of AF.
  
  
  RESULTS
  AF was maintained for 3 weeks (short term [ST], persistent AF) or 6 months (long term [LT], permanent AF). Fibrillation patterns were assessed with epicardial mapping. The origin of fibrillation waves and sites of conduction abnormalities were more homogeneously distributed in LT than in ST goats. Histologically, the total area fraction occupied by fibrous tissue and the degree of perimysial fibrosis (separation between myocyte bundles) were not significantly different between groups. However, endomysial fibrosis (distance between myocytes within bundles) was significantly larger in LT goats, particularly in the outer millimeter of the atria. By contrast, myocyte diameters were larger in LT goats throughout the atrial walls. High-resolution optical mapping showed that epicardial wavefront expansion was slower and more anisotropic in LT than in ST goats. Finally, a mathematical model of a simplified atrial architecture confirmed the potential impact of epicardial endomysial fibrosis on AF complexity.
  
  
  CONCLUSIONS
  Altered propagation after 6 months of AF is consistent with homogeneous structural remodeling in the outer millimeter of the atria. Loss of continuity of the epicardial layer because of endomysial fibrosis may reduce its synchronizing effect, thereby increasing the complexity of fibrillatory conduction pathways. The exact distribution of fibrosis may be more important for the occurrence of conduction disturbances than the overall quantity.
authors: Department of Physiology, Maastricht University, Maastricht, the Netherlands. s.verheule@maastrichtuniversity.nl
authors: Sander
authors: S
authors: Verheule
authors: Els
authors: E
authors: Tuyls
authors: Ali
authors: A
authors: Gharaviri
authors: Sarah
authors: S
authors: Hulsmans
authors: Arne
authors: A
authors: van Hunnik
authors: Marion
authors: M
authors: Kuiper
authors: Jan
authors: J
authors: Serroyen
authors: Stef
authors: S
authors: Zeemering
authors: Nico H L
authors: NH
authors: Kuijpers
authors: Ulrich
authors: U
authors: Schotten
mesh_terms: D000200:Action Potentials; D000818:Animals; D001281:Atrial Fibrillation / Q000209:etiology / Q000473:pathology / Q000503:physiopathology*; D016275:Atrial Function; D002304:Cardiac Pacing, Artificial; D004195:Disease Models, Animal; D005355:Fibrosis; D006041:Goats; D006325:Heart Atria / Q000473:pathology / Q000503:physiopathology; D008955:Models, Cardiovascular; D010496:Pericardium / Q000473:pathology / Q000503:physiopathology*; D013997:Time Factors; D056969:Voltage-Sensitive Dye Imaging