title: Myocardial compliance was not altered after acute induction of atrial fibrillation in sheep.
abstract: BACKGROUND
  Although left ventricular (LV) contractility in atrial fibrillation (Af) is known to change in a beat-to-beat fashion, little is known about the changes in LV compliance in Af.
  
  
  METHODS
  We experimentally induced tachycardic Af (average heart rate - 154 beats per minute) in 18 sheep. LV volume and pressure were simultaneously monitored using a conductance catheter. LV end-diastolic volume (V(ED)) and pressure (P(ED)) were plotted in a beat-to-beat fashion and fitted to the following exponential equation (P(ED)=gamma x e(b x V(ED))) in each animal. A random effects model was constructed to determine if the intercepts and slopes differ.
  
  
  RESULTS
  In all animals, those plots after the induction of Af fit quite well to the exponential function (r=0.834+/-0.184) by gating short preceding interval (RR1) beats. By simply taking the natural logarithm of both sides in the equation, the linear relationship (ln(P(ED)) =alpha+ betaxV(ED), where a = lng) was observed in all animals before (normal sinus rhythm, NSR) and after the induction of Af. Only two of 18 intercepts and four of 18 slopes deviate between NSR and Af. Most interestingly, the random effects model clearly detailed that the average animal had intercepts and slopes that were not discernibly different between NSR and Af.
  
  
  CONCLUSIONS
  Unlike LV contractility, myocardial compliance did not change after the acute induction of Af. These interesting results may give us insights into the understanding of the physiology in acute rapid Af.
authors.affiliation: Department of Biomedical Engineering, Lerner Research Institute, Cleveland, Ohio 44195, USA.
authors.forename: Masami
authors.initials: M
authors.lastname: Takagaki
authors.forename: Patrick M
authors.initials: PM
authors.lastname: McCarthy
authors.forename: Masahiro
authors.initials: M
authors.lastname: Inoue
authors.forename: Mina
authors.initials: M
authors.lastname: Chung
authors.forename: Jason T
authors.initials: JT
authors.lastname: Connor
authors.forename: Raymond
authors.initials: R
authors.lastname: Dessoffy
authors.forename: Yoshie
authors.initials: Y
authors.lastname: Ochiai
authors.forename: Michael
authors.initials: M
authors.lastname: Howard
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Doi
authors.forename: Michael
authors.initials: M
authors.lastname: Kopcak
authors.forename: Todor N
authors.initials: TN
authors.lastname: Mazgalev
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Fukamachi
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000503:physiopathology*; D001794:Blood Pressure / Q000502:physiology; D003971:Diastole; D004195:Disease Models, Animal; D004562:Electrocardiography; D006321:Heart / Q000503:physiopathology*; D006439:Hemodynamics; D009200:Myocardial Contraction / Q000502:physiology*; D012756:Sheep; D016277:Ventricular Function, Left