Final Feigenbaum’s Echocardiography DIGITAL

Chapter 5 Evaluation of Systolic Function of the Left Ventricle

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Chapter 5 Evaluation of Systolic Function of the Left Ventricle

Evaluation of Systolic Function of the Left Ventricle

FIGURE 5.19. Multiple two-dimensional imaging planes have been extracted from a full-volume three-dimensional dataset. The upper panels show apical four- and two- chamber views and a single short-axis image which have been extracted from the full-volume dataset. At the lower right is a series of nine short-axis images which correspond to the horizontal lines in the apical views. The lower graph depicts the instantaneous volume change for multiple ana- lyzed segments.

the cardiac cycle is referred to as deformation analysis. Deformation can be characterized by myocardial strain, strain rate, or torsion, each of which de nes a di erent parameter of shape change with contraction and relaxation. ese parameters of function are derived from analysis of motion (strain) or velocity (strain rate) at two or more myocar- dial regions from which strain and other advanced parameters can be calculated. Strain may be calculated in any of three orthogonal planes, representing longitudinal, circumferential, and radial con- traction (Fig. 5.20). Strain is de ned as the normalized change in length between two points (Fig. 5.21). Negative strain implies short- ening of a segment (contraction) and positive strain lengthening of a segment (relaxation). As such, normal contraction is de ned by negative longitudinal systolic strain followed by biphasic diastolic strain related to early and late diastolic lling, respectively. Normal radial strain, reƒecting wall thickening is positive in systole. Strain rate represents the change in velocity between two adjacent points. Strain and strain rate can each be calculated either from Doppler tissue imaging or from speckle tracking techniques and displayed in a multitude of formats (Figs. 5.22 to 5.24). Because of poor signal to noise ratios and other factors most current platforms rely on speckle tracking rather than tissue Doppler techniques. It should be empha- sized that for Doppler tissue imaging, the initial raw data represent myocardial velocity at a point in space within the interrogating beam. To calculate distance, this velocity is integrated over time. If two dis- crete points within a region of interest are compared for change in velocity over the cardiac cycle, strain rate is the primary parameter obtained. Strain, or the change in distance between the two points is, therefore, the derived variable. Conversely, with speckle tracking it is the actual location of discrete myocardial segments (rather than the velocity) that is calculated. As such, the primary calculation is of tissue displacement. If two points are simultaneously compared for their location, the primary parameter derived is strain rather than strain rate. With speckle tracking, strain rate can be derived from the original data by calculating the rate of change in location over time (velocity) for two adjacent points. With either technique, regions of interest can vary from 5 to 6 mm to 2 to 3 cm in length. Using current generation platforms, the typical method by which longitudinal strain is calculated is to acquire an apical four-chamber, two-chamber and apical long-axis view of the le“ ventricle. Each of these views is then subjected to speckle tracking analysis to assess longitudinal strain in discrete segments. Assessment of end-systolic

strain requires identi cation of end-systole. e current recommen- dation is that timing of end-systole be determined from Doppler of the le“ ventricular overƒow tract and de ned as aortic valve closure (Fig. 5.22). e current recommendation for global longitudinal strain (GLS) is that it be calculated on an 18-segment model with part of the apex being represented in each of six segments represent- ing the apical third of the le“ ventricle. Individual strain can be plot- ted over the cardiac cycle for each segment and GLS calculated as the average longitudinal strain in each of the 18 segments (Fig. 5.23). While strain can be calculated either in the longitudinal, cir- cumferential, or radial dimensions, most commercially available

FIGURE 5.20. Schematic demonstration of the three orthogonally directed strain calcula- tions. Longitudinal strain ( ε L ) is defined as along the long axis of the left ventricle. Radial strain ( ε R ) is orthogonal to the longitudinal strain and oriented perpendicular to the endo- cardial border. Circumferential strain ( ε C ), calculated in the short axis of the ventricle, is parallel to the radius of the ventricle. The curved arrows outside the schematic depict the normal clockwise basal and counterclockwise apical twisting of the left ventricle.

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