title: Mind the model: effect of instrumentation on inducibility of atrial fibrillation in a sheep model.
abstract: BACKGROUND
  Atrial electrical remodeling, shortening of the atrial effective refractory period (AERP) underlying atrial fibrillation (AF) has been described in different animal models. However, there remains some controversy regarding the time course of this electrical remodeling and the need for secondary factors in the development of AF. We investigated the effect of instrumentation on the inducibility of AF. We hypothesized that epicardial instrumentation could be a confounding factor that accelerates the development of AF.
  
  
  RESULTS
  Thirty sheep were rapidly atrially paced at 600 beats/min for 15 weeks: 15 were endocardially instrumented and paced (endo), and 15 were both endocardially and epicardially instrumented. Six of these animals were endocardially paced (sham) and 9 were epicardially paced (epi). The underlying rhythm was determined at regular intervals, and electrophysiologic study was performed. AF developed significantly faster in the epi group. After 3 weeks of pacing, the cumulative incidence of sustained AF (>1 hour) already was 70% in this group versus only 14% and 20% in the endo and sham groups, respectively. After 15 weeks of pacing, this difference was no longer evident. Baseline AERP and minimal AERP, reached before the development of AF, were not significantly different in the three groups. Epicardial instrumentation (epi and sham) increased baseline left and right atrial pressures, but only epicardial stimulation (epi) led to early development of AF.
  
  
  CONCLUSIONS
  In this sheep model of AF, the experimental setup is a major determinant of the inducibility of AF. Not epicardial instrumentation per se but epicardial stimulation accelerated the development of AF. Different animal models
authors.affiliation: Department of Cardiology, University Hospital Gasthuisberg, University of Leuven, Belgium.
authors.forename: Rik
authors.initials: R
authors.lastname: Willems
authors.forename: Patricia
authors.initials: P
authors.lastname: Holemans
authors.forename: Hugo
authors.initials: H
authors.lastname: Ector
authors.forename: Karin R
authors.initials: KR
authors.lastname: Sipido
authors.forename: Frans
authors.initials: F
authors.lastname: Van de Werf
authors.forename: Hein
authors.initials: H
authors.lastname: Heidbüchel
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000503:physiopathology* / Q000523:psychology*; D001794:Blood Pressure; D002304:Cardiac Pacing, Artificial; D004195:Disease Models, Animal; D015716:Electrocardiography, Ambulatory; D004567:Electrodes, Implanted; D004594:Electrophysiology / Q000295:instrumentation*; D004699:Endocardium / Q000502:physiology; D005260:Female; D010493:Pericarditis / Q000503:physiopathology; D010496:Pericardium / Q000502:physiology; D011669:Pulmonary Wedge Pressure / Q000502:physiology; D012032:Refractory Period, Electrophysiological / Q000502:physiology; D012756:Sheep; D020257:Ventricular Remodeling