Noninvasive assessment of left ventricular force-frequency relationships using tissue Doppler-derived isovolumic acceleration: validation in an animal model.
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.
Vogel
Michael
M
Cardiothoracic Unit, Great Ormond Street Hospital for Children, NHS Trust, London, UK.
Cheung
Michael M H
MM
Li
Jia
J
Kristiansen
Steen B
SB
Schmidt
Michael R
MR
White
Paul A
PA
Sorensen
Keld
K
Redington
Andrew N
AN
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