Left ventricular strain and peak systolic velocity: responses to controlled changes in load and contractility, explored in a porcine model

Cardiovascular Ultrasound, May 2012

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, 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. Methods Thirteen 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. Results Peak 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. Conclusions 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, 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.

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Left ventricular strain and peak systolic velocity: responses to controlled changes in load and contractility, explored in a porcine model

Cardiovascular Ultrasound Left ventricular strain and peak systolic velocity: responses to controlled changes in load and contractility, explored in a porcine model Roman A'roch 0 3 Ulf Gustafsson 2 Gran Johansson 1 Jan Poelaert 5 Michael Haney 4 0 Department of Surgical and Perioperative Sciences, Anaesthesiology and Intensive Care Medicine, University Hospital of Umea , Umea , Sweden 1 Department of Surgical and Perioperative Sciences, Anaesthesiology and Intensive Care Medicine, University Hospital of Umea , Umea , Sweden 2 Department of Clinical Physiology, Heart Centre, University Hospital of Umea , Umea , Sweden 3 Department of Surgical and Perioperative Sciences, Anaesthesiology and Intensive Care Medicine, University Hospital of Umea , Umea , Sweden 4 Department of Surgical and Perioperative Sciences, Anaesthesiology and Intensive Care Medicine, University Hospital of Umea , Umea , Sweden 5 Department of Anaesthesiology and Perioperative Medicine, University Hospital of Brussels , Brussels , Belgium 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, 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. Methods: Thirteen 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. Results: Peak 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. Conclusions: 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, 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. Tissue velocities echocardiography; Ventricular function; Load - Introduction 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 [2-5]. Myocardial velocity is the most widely used and validated parameter from this method [6-8]. Through further derivation and integration of tissue velocities, additional parameters like displacement, strain rate and strain can be calculated. Strain is a dimensionless quantity, which is the product of stress. It represents the fractional change (or percentage) from the original or unstressed dimension. Positive strain indicates expansion or lengthening and negative strain compression or shortening. An ideal index of myocardial contractility should be independent of loading conditions (preload and afterload), heart size and mass, and sensitive to changes in inotropy [9]. In this study, we have focused only on the issue of systolic velocities and load, since the loaddependence of diastolic tissue velocities has been well demonstrated [10,11]. The issue of load-dependency and tissue velocities during systole has been raised earlier, and clinical findings have been published that support the id (...truncated)


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Roman A’roch, Ulf Gustafsson, Göran Johansson, Jan Poelaert, Michael Haney. Left ventricular strain and peak systolic velocity: responses to controlled changes in load and contractility, explored in a porcine model, Cardiovascular Ultrasound, 2012, pp. 22, 10, DOI: 10.1186/1476-7120-10-22