title: Myocardial contractility is not constant during spontaneous atrial fibrillation in patients.
abstract: BACKGROUND
  The variation in stroke volume and pulse pressure characteristic of atrial fibrillation is usually ascribed to time-dependent ventricular filling, implying a single positive relationship between end-systolic pressure and volume, which defines a single state of myocardial contractility. We tested the hypothesis that contractility also varies.
  
  
  RESULTS
  We measured the left ventricular pressure and volume continuously with a conductance catheter with catheter-tip micromanometer introduced retrogradely into the left ventricle. The end-systolic pressure-volume relationship was determined in 6 patients in atrial fibrillation undergoing cardiac catheterization for diagnostic purposes and 4 control patients in sinus rhythm undergoing coronary artery bypass graft surgery. The normal positive relationship between end-systolic pressure and volume was found in the control patients, but no such positive relationship was found in any patient in atrial fibrillation. In the latter, the slopes of the linear regressions were either not significantly different from zero or significantly negative (r values <0.08), both results indicating a change in contractility from beat to beat. Significantly negative relationships were found between end-systolic volume and preceding R-R interval (-0.82<r<-0.24), indicating the presence of mechanical restitution. Significantly positive relationships were found between end-systolic volume and the R-R interval before the preceding R-R interval (0.35<r<0.74), indicating the presence of postextrasystolic potentiation.
  
  
  CONCLUSIONS
  Myocardial contractility is constantly changing from beat to beat in atrial fibrillation because of the influence of the force-interval relationships.
authors.affiliation: National Heart and Lung Institute, Imperial College School of Medicine,Royal Brompton and Charing Cross Hospitals, London, UK.
authors.forename: C I
authors.initials: CI
authors.lastname: Brookes
authors.forename: P A
authors.initials: PA
authors.lastname: White
authors.forename: M
authors.initials: M
authors.lastname: Staples
authors.forename: P J
authors.initials: PJ
authors.lastname: Oldershaw
authors.forename: A N
authors.initials: AN
authors.lastname: Redington
authors.forename: P D
authors.initials: PD
authors.lastname: Collins
authors.forename: M I
authors.initials: MI
authors.lastname: Noble
mesh_terms: D000368:Aged; D001281:Atrial Fibrillation / Q000503:physiopathology*; D006328:Cardiac Catheterization; D016022:Case-Control Studies; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology*; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology