title: Noninvasive assessment of left ventricular force-frequency relationships using tissue Doppler-derived isovolumic acceleration: validation in an animal model.
abstract: BACKGROUND
  We have demonstrated that myocardial acceleration during isovolumic contraction (IVA) is a sensitive index of right ventricular contractile function. In this study, we assessed the usefulness of IVA to measure left ventricular (LV) contractile function and force-frequency relationships in an experimental preparation.
  
  
  RESULTS
  In study 1, we examined 6 pigs by use of tissue Doppler imaging of LV free wall and simultaneous measurements of intraventricular pressure, volume, maximal elastance (Emax), and dP/dtmax by conductance catheterization. Animals were paced via the right atrium at a rate of 130 bpm. IVA was compared with elastance during contractility modulation by esmolol and dobutamine and assessed during preload reduction and afterload increase. In study 2, in 6 more pigs, force-frequency data were obtained during incremental atrial pacing from 120 to 180 bpm. Study 1: Esmolol led to a decrease in IVA and Emax (P<0.03 and <0.02, respectively), both of which increased during dobutamine infusion (P<0.02 and <0.03, respectively). IVA was unaffected by significant (P<0.001) acute reduction of LV volume and a significantly increased LV afterload (systolic pressure increase, P<0.001). Study 2: There was a positive correlation between IVA and dP/dtmax (r2=0.92, P<0.05). As heart rate was increased from 120 to 160 bpm, there were significant increases in both IVA and dP/dtmax (P<0.0004 and P=0.02, respectively). Over the same range of heart rates, there was no significant change in Emax (P=0.22).
  
  
  CONCLUSIONS
  IVA is a measurement of LV contractile function that is unaffected by preload and afterload changes within a physiological range and can be used noninvasively to measure LV force-frequency relationships.
authors.affiliation: Cardiothoracic Unit, Great Ormond Street Hospital for Children, NHS Trust, London, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Vogel
authors.forename: Michael M H
authors.initials: MM
authors.lastname: Cheung
authors.forename: Jia
authors.initials: J
authors.lastname: Li
authors.forename: Steen B
authors.initials: SB
authors.lastname: Kristiansen
authors.forename: Michael R
authors.initials: MR
authors.lastname: Schmidt
authors.forename: Paul A
authors.initials: PA
authors.lastname: White
authors.forename: Keld
authors.initials: K
authors.lastname: Sorensen
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Redington
mesh_terms: D000818:Animals; D002304:Cardiac Pacing, Artificial; D015150:Echocardiography, Doppler / Q000379:methods*; D006352:Heart Ventricles / Q000000981:diagnostic imaging*; D009200:Myocardial Contraction; D015588:Observer Variation; D013552:Swine; D016276:Ventricular Function; D016277:Ventricular Function, Left; D017725:Ventricular Pressure