Assessment Of Systolic Function By Twodimensional Echocardiography

Because 2D echocardiography enables visualization of the entire LV perimeter in multiple planes, it is significantly superior to M-mode approaches for the measurement of cardiac chamber volumes and EF.37-40 Numerous algorithms have been applied to calculate LV volumes by echocardiography Fig. 13-21).

Most such algorithms have assumed that the LV conforms to the shape of a prolate ellipsoid and calculated volume by diameter-length or area-length formulas.384! Multiple studies comparing LV volume calculated by area-length methods to those obtained by other techniques have yielded good correlations, with the best results obtained utilizing biplane apical views.41,42 Other algorithms have assumed an LV cavity configuration that is a combination of geometric shapes, such as a cylinder-cone or a cylinder-hemiellipse.4143 Currently, the most commonly used algorithm to calculate LV volumes is based upon the Simpson rule, which derives measurements by dividing the LV by parallel planes into a number of small segments and then summating the area of the individual disks. This approach has the advantage of making no assumptions about the geometry of the ventricle. A number of modifications of the basic Simpson rule method have been applied to calculate LV volumes. Although all have yielded good results, the optimal correlations have been achieved with a modification that separately quantifies the volume of the apex as an ellipsoid.40-45

Regardless of the methodologic approach used, accurate calculations of LV volumes by echocardiography require attention to detail and are critically dependent upon high-quality images to delineate the endocardium and image the entire LV perimeter. As a rule, echocardiographic estimates of LV volumes underestimate those calculated by other techniques and are most accurate in the absence of significant alterations of LV size and contraction. End-systolic measurements are more accurate than those made at end-diastole, probably owing to superior endocardial definition. Nevertheless, echocardiographic calculations of LV volumes have generally yielded correlation coefficients in excess of 0.75 as compared with radionuclide angiography, cineangiography, and autopsy studies regardless of the algorithm employed.37-45 Of importance, calculation of LV volumes generally yields values with a standard error of estimate that renders these measurements suitable for clinical decision making in the care of most patients.

In an attempt to refine and facilitate the derivation of LV volume measurements from echocardiography, a number of technical developments have been evaluated. Images of the power spectrum of the Doppler signal produced by contraction/relaxation and colorization of the B-mode tissue image have been utilized to visualize the endocardial surface.46 These techniques have been reported to be useful in identifying endocardial signals, particularly in patients with suboptimal tissue images. Greater enhancement of endocardial border delineation and improvement of the reliability of measures of LV size and contraction has been achieved through utilization of tissue harmonic imaging and by the injection of ultrasonic contrast agents to produce LV cavity opacification.18a46a A software package that provides instantaneous and automated endocardial border delineation throughout the cardiac cycle has been developed based upon the display of tissue signals as backscatter rather than specular reflection.47 This technique of automated quantitation can yield continuous measurements of LV volume throughout the cardiac cycle and can derive values for ejection fraction, ejection rate, and rate of filling during diastole Fig. 13-22). This same technology has been utilized to display endocardial excursion throughout systolic contraction or diastolic expansion in a color format superimposed upon the tissue image Fig. 13-23, Plate 53). This technique has proved to be of value in the recognition of abnormalities of LV contraction and regional disturbances of LV diastolic function.4849-49a Finally, studies employing 3D echocardiography have reported improved reproducibility of measures over 2D methods. Although these technical developments are relatively untested, they promise to facilitate the quantitative assessment of LV size and function from routine echocardiograms.

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