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1 Cardiovascular Institute, University of Pittsburgh, Pittsburgh, PA, USA
* To whom correspondence should be addressed. E-mail: gorcsanj{at}upmc.edu.
The Tei index is clinically useful to quantify left ventricular (LV) function but it is limited because it cannot be recorded over a single cardiac cycle. A related myocardial performance index using tissue Doppler (TD-MPI) can be rapidly calculated and determine beat-to-beat changes, however, its ability to quantify contractility and the effects of loading have not been determined. Our aim was to test the hypothesis that TD-MPI can quality contractile state, but is affected by acute alterations in loading, using LV pressure-volume relations in an animal model. Eight dogs were studied using mitral annular tissue Doppler, high fidelity pressure and conductance catheters. LV TD-MPI was calculated as (a'-b')/b' where (a) was the duration of mitral annular velocity during diastole and (b) was the duration of the systolic wave. End-systolic elastance (Ees), the time constant of isovolumic relaxation (Tau), peak positive and negative dP/dt (dP/dtmax and min) were used as measures of LV function. Data were obtained at baseline, dobutamine and esmolol infusion to alter contractile state, and inferior vena cava occlusion and aortic occlusion to alter preload and afterload. LV TD-MPI decreased from 0.83±0.19 to 0.62±0.20* with dobutamine and increased to 1.19±0.26* with esmolol. LV TD-MPI significantly correlated with dP/dtmax (r=-0.76*), Ees (r=-0.68*), dP/dtmin (r=0.82*), and Tau (r=0.78*), however, it was affected by decreases in preload (from 0.83±0.19 to 1.09±0.36*) and increases in afterload (to 1.23±0.17*, *p<0.05). In conclusion, LV TD-MPI can rapidly quantify alterations in LV contractile state, but is affected by acute alterations in preload and afterload.
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