Abstract
BackgroundTissue 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, though 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 (both preload and afterload) and change in inotropic state on peak systolic velocity and strain as a measure of LV contractility.MethodsThirteen anesthetized juvenile pigs were studied, using direct measurement of left ventricular pressure and volume and transthoracic echocardiography. Transient inflation of a vena cava balloon catheter produced controlled load alterations. At least eight consecutive beats in the sequence were analyzed with tissue velocity echocardiography during the load alteration and analyzed for change in peak systolic velocities and strain during same contractile status with a controlled load alteration. Two pharmacological inotropic interventions were also included to generate several myocardial contractile conditions in each animal.ResultsPeak systolic velocities reflected the drug-induced changes in contractility in both radial and longitudinal axis. During the acute load change, the peak systolic velocities 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 velocity, longitudinal axis, control group beat 1-5.72 ± 1.36 with beat 8–6.49 ± 1.28 cm/sec, 95% confidence interval), with the single exception of the negative inotropic intervention group where peak systolic velocity decreased a small amount during load reduction (beat 1–3.98 ± 0.92 with beat 8–2.72 ± 0.89 cm/sec). Systolic strain, however, showed a clear degree of load-dependence.ConclusionsPeak 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, in a controlled experimental model where successive beats during load alteration are assessed, has a strong relation to contractility. Peak systolic velocity, but not peak strain rate, is largely independent of load, in this model. More study is needed to confirm this finding in the clinical setting.
Highlights
Since its introduction tissue velocity echocardiography (TVE) has opened new possibilities for non-invasive quantification of myocardial function [1]
Load changes were achieved by the VCBO, where the first eight beats in the sequences (Figure 1) are analyzed and a clear load alteration is shown, and this was consistent with all 3 inotropic conditions and in both projections (Figure 2)
The main findings in this study were that peak systolic velocity (PSV) was loadindependent in this model
Summary
Since its introduction tissue velocity echocardiography (TVE) has opened new possibilities for non-invasive quantification of myocardial function [1]. Tissue Doppler echocardiography is an established cardiac diagnostic method for measurement and characterization of both the systolic and diastolic cardiac dysfunction [2,3,4,5]. Strain is a dimensionless quantity, which is the product of stress. It represents the fractional change (or percentage) from the original or unstressed dimension. We sought to characterize the effects of acute load change (both preload and afterload) and change in inotropic state on peak systolic velocity and strain as a measure of LV contractility
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