Page 17 - The role of advanced echocardiography in patients with ischemic heart disease - Rachid Abou

INTRODUCTION
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Non-invasive evaluation of left ventricular (LV) systolic function by echocardiography remains one of the most pivotal measures in clinical cardiology. Although conventionally quantified by means of the LV ejection fraction (EF), it has become evident that this parameter is subject to a number of limitations. LVEF can be normal in the presence of impaired LV systolic function, since it does not reflect intrinsic myocardial contractility.1 In addition, LVEF is highly load-dependent, and suffers from significant intra- and inter-observer variability.2 Assessment of myocardial strain can potentially overcome many of the limitations of LVEF in assessing LV systolic function. Speckle tracking echocardiography permits assessment of myocardial strain in 3 spatial directions (longitudinal, radial and circumferential) independent of the angle of insonation of the ultrasound beam. Longitudinal strain is probably the most frequently type of strain used to characterise LV systolic function in clinical practice. This review article focuses on the practical aspects of measuring LV global longitudinal strain (GLS), reviews the clinical implications of impaired LV GLS strain and provides a glimpse into the future clinical applications of this technology.
ASSESSMENT OF LEFT VENTRICULAR GLOBAL LONGITUDINAL STRAIN
The LV myocardium consists of two helical, opposing layers of myocardial fibres (endocardial/right-handed and epicardial/left-handed) surrounding a circumferential, mid-ventricular layer. When these layers contract, the myocardium shortens in the longitudinal and circumferential directions and thickens in the radial direction (Figure 1).
The introduction of speckle tracking echocardiography has allowed for a more comprehensive analysis of LV systolic function when compared to LVEF by assessing myocardial deformation in these 3 directions. Speckle tracking echocardiography can be performed off-line on 2-dimensional echocardiographic data by tracking myocardial “features” throughout the cardiac cycle. Strain can be measured in different directions (longitudinal, circumferential and radial), and is conventionally expressed as a percentage, defined as relative change in length/thickness of the LV myocardium in relation to its original length/thickness (i.e. it is unitless). LV GLS is calculated from 4-, 3- and 2-chamber apical views (Figure 2), whereas LV global circumferential strain and LV global radial strain are computed from short-axis images. LV GLS measured with speckle tracking echocardiography has the largest body of evidence in clinical
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