Strain and peak systolic velocities : relation to load in a porcine model

• Background:  Tissue velocity echocardiography is increasingly used to evaluate global and regional cardiac function.  Previous studies have suggested that the quantitative measurements obtained during ejection are reliable indices of contractility.  Their load-sensitivity has been studied in different settings, but still remains a matter of controversy.  We sought to characterize the effects of acute load change and change in inotropic state on peak systolic velocity and strain as a measure of LV contractility, and particularly to determine if these parameters were load-dependent. Methods: Thirteen anesthetised juvenile pigs were studied, using direct measurement of left ventricular (LV) pressure and volume and transthoracic echocardiography. Transient inflation of a vena cava balloon catheter produced controlled preload alterations.  At least eight consecutive beats in the preload alteration sequence were analysed with tissue velocity echocardiography (TVE) during the preload alteration and analysed for change in peak systolic velocities (PSV) and strain (e) during same contractile status with a controlled preload alteration.  Two pharmacological inotropic interventions were also included to generate several myocardial contractile conditions in each animal. Results: PSV reflected the drug-induced changes in contractility in both radial and longitudinal axis.  During the acute load change, the PSV remain stable when derived from signal in the longitudinal axis and from the radial axis.  The peak systolic velocity parameter demonstrated no strong relation to either load or inotropic intervention, that is, it remained unchanged when load was systematically and progressively varied.  Peak systolic strain, however, showed a clear degree of load-dependence. Conclusion:  Peak systolic velocity appears to be load-independent as tested by beat to beat load reduction, while peak systolic strain appears to be load-dependent in this model.  Peak systolic velocity has a strong relation to contractility, independent of load, in serial measures, in this model.  More study is needed to confirm this in the clinical setting.

Nyckelord

tissue velocities echocardiography

ventricular function

load

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