Final Feigenbaum’s Echocardiography DIGITAL

Feigenbaum’s Echocardiography

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Feigenbaum’s Echocardiography

FIGURE 5.21. Demonstration of strain in a schematized myocardial segment. Both longitudinal strain ( ε L ) and radial strain ( ε R ) are calculated. Assuming a baseline length of 2 cm with contraction the myocardial segment decreases in length to 1.6 cm resulting in a longitudinal strain of –20%. If the same fiber has lengthening (as noted on the left ) to a 2.2 cm, longitudinal strain is calcu- lated to + 10%. Radial strain is calculated perpendicular to the long axis and, in this instance, thickening of the myocardial segment from 1 to 1.4 cm results in a radial strain of + 40%. Note that with normal contraction, there is shortening in length but increase in width of the myocar- dial segment and, as such, normal longitudinal strain is negative and normal radial strain positive.

platforms provide only analysis of longitudinal strain. Because ultrasound platforms use proprietary algorithms for calculation of strain, initially there was substantial variability in normal ranges across platforms. More recently signi cant standardization has occurred and GLS appears to be fairly reproducible and equiva- lent across multiple ultrasound platforms. In addition, studies have demonstrated that GLS is more reproducible and provides a more reliable, reproducible parameter for following ventricular function in a broad spectrum of disease than does radial strain or strain rate. Strain, like most parameters of systolic function, is not uniform among all myocardial segments. Myocardial velocities and displace- ment have a gradation in magnitude from base to apex, with basal parameters being higher than apical values. Longitudinal strain, de ned as motion parallel to the long axis has less variability apex to base but varies substantially around the circumference of the le ven- tricle, with higher strain in the anterior and lateral walls compared to the inferior and septal wall. Normal longitudinal strain averages –20%and is numerically less than normal radial strain. ere is a well- described base to apex variation in strain in normals which has varied in magnitude based on the ultrasound platform used and technique (tissue Doppler vs. speckle tracking). is lack of uniformity proba- bly relates to a combination of factors, including angle dependency with tissue Doppler, length of segment analyzed, and incorporation of annular or pericardial tissue in the region of interest. If Doppler

tissue imaging is used to calculate myocardial velocity, there will be angle dependency of the velocity determination which becomes more pronounced at the apical segments where ultrasound beam interro- gates a wall curve. At the true apex, the beam intersects the myocar- dium at 90 degrees and longitudinal strain precipitously declines if assessed with Doppler tissue techniques. For this and other reasons, including a more favorable signal to noise ratio, speckle tracking has largely replaced Doppler tissue imaging for determination of myo- cardial strain. While remaining preload dependent, both strain and strain rate imaging are more sensitive and earlier indicators of abnor- mal myocardial function than is assessment of wall thickening alone. is has been demonstrated experimentally as well as during sponta- neous or induced myocardial ischemia. A signi cant limitation to analysis of strain or strain rate is the heterogeneity of normal values within the myocardium as well as patient-to-patient variability resulting in a broad range of normal values. As such, subtle deviations from “normal” must be inter- preted within clinical context and serial changes within a given patient may have more diagnostic value. Quantitation of myocardial strain is highly dependent on image quality, probably to a greater degree than less sophisticated quantitative techniques. While largely automated, signi cant user interaction is frequently necessary to ensure accurate myocardial tracking (Fig. 5.25). In studies with poor image quality, it may not be possible to obtain valid data.

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FIGURE 5.22. Apical four-chamber view from which longitudinal strain has been obtained in seven seg- ments. The image at the upper left is the apical four-chamber view. The mid myocardium is noted by the dotted line . Below the apical four-chamber view is a graphic representation of each of the seven segments as well as the global strain for the apical four-chamber view. The vertical line (AVC) denotes end-systole. At the lower right is a Doppler of the left ventricular outflow tract from which the time from onset of QRS to aortic valve closure has been calcu- lated as 387 ms. To define end-systole. At the upper right are the simultaneously obtained volumetric mea- surements of left ventricular volume from which the ejection fraction is calculated to be 62.2%.

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