title: Frank-Starling mechanism contributes modestly to ventricular performance during atrial fibrillation.
abstract: OBJECTIVE
  The aim of this study was to assess whether Frank-Starling mechanism has an independent effect on left ventricular (LV) performance in atrial fibrillation (AF).
  
  
  BACKGROUND
  Ventricular performance in AF depends on variable contractility through the interval-force mechanism based on the ratio of preceding and pre-preceding RR intervals (RR(p)/RR(pp)). The impact of end-diastolic volume (EDV) variability, through the Frank-Starling mechanism, is not well understood.
  
  
  METHODS
  We induced AF in 16 open chest dogs. RR intervals, LV pressure, LV volume, and aortic flow were collected for >400 beats during rapid AF (ventricular cycle length 292 +/- 66 ms). In six of the dogs, additional data were collected while average ventricular cycle length was prolonged from 258 +/- 34 ms to 445 +/- 80 ms by selective vagal nerve stimulation of the AV node.
  
  
  RESULTS
  The relations of maximal LV power (LVPower) and peak LV pressure derivative (dP/dt) versus RR(p)/RR(pp) were fitted to the equation y = A * (1 - EXP (RR(p)/RR(pp)min - RR(p)/RR(pp))/C) and the residuals (RES) of these relations were analyzed. LVPower and dP/dt strongly correlated with RR(p)/RR(pp) (r(2) = 0.67 +/- 0.12 and 0.66 +/- 0.12, P < .0001 for all correlations). Importantly, RES-LVPower and RES-dP/dt showed linear correlation with EDV (r(2) = 0.20 +/- 0.14 and r(2) = 0.24 +/- 0.17, P < .01 for all correlations). In the six dogs with slowed average ventricular rate, the slope of both residual relationships (RES-LVPower vs EDV and RES- dP/dt vs EDV) decreased (P < .03 for both).
  
  
  CONCLUSIONS
  The Frank-Starling mechanism contributes to ventricular performance in AF independently of the interval-force effects of the beat-to-beat variability in cardiac contractility. The Frank-Starling mechanism is sensitive to the average ventricular rate.
authors.affiliation: Department of Cardiovascular Medicine, The Cleveland Clinic Foundation, Ohio 44195, USA.
authors.forename: Zoran B
authors.initials: ZB
authors.lastname: Popović
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Yamada
authors.forename: Kent A
authors.initials: KA
authors.lastname: Mowrey
authors.forename: Youhua
authors.initials: Y
authors.lastname: Zhang
authors.forename: Don W
authors.initials: DW
authors.lastname: Wallick
authors.forename: Richard A
authors.initials: RA
authors.lastname: Grimm
authors.forename: James D
authors.initials: JD
authors.lastname: Thomas
authors.forename: Todor N
authors.initials: TN
authors.lastname: Mazgalev
mesh_terms: D000200:Action Potentials; D000818:Animals; D001281:Atrial Fibrillation / Q000503:physiopathology* / Q000628:therapy; D004285:Dogs; D022062:Electrophysiologic Techniques, Cardiac; D006439:Hemodynamics; D023421:Models, Animal; D008955:Models, Cardiovascular; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium; D016276:Ventricular Function; D016277:Ventricular Function, Left / Q000502:physiology*