DK2985_C000 1..28 - AlSharqia Echo Club

36 Transesophageal Echocardiographyflow, the focal zone must be kept at or below the interrogatedarea (1).By displaying flow patterns, color provides an indicatorfor adequate positioning of the beam in order to performquantitative spectral Doppler measurements. As theimages obtained are 2D, it is important to visualize theflows in different planes to reconstitute the 3D structureof a given flow jet. A flow in a vessel crossing the entirescreen, although uniform, will appear under differentcolors as the angle of the flow with the different scanlines changes along its visible course. For instance, on a908 image of the descending thoracic aorta, the flow willbe colored in red on the right-hand side of the screenwhere it comes toward the transducer but in blue on theleft part of the screen, where it moves away from thetransducer.It is important to remember that color flow display is avelocity mapping and not an actual blood volumemeasurement. Area and brightness on the screen are determinedonly by the speed of blood, which is the result of aninstantaneous pressure gradient between upstream anddownstream cavities (7). A small mitral regurgitation(MR) orifice, in the context of a normal left ventricularfunction, will create a high-velocity jet (6 m/s) into theleft atrium (LA) appearing larger than the real regurgitantblood volume. This is due to the sweeping of left atrialblood by the regurgitant jet. Color image in severemitral insufficiency with poor left ventricular functionwill underestimate the amount of regurgitant bloodbecause of smaller pressure gradient. Moreover, the velocitymeasured in a precise vessel does not take intoaccount the real flow profile (which is not flat exceptcloser to the root of great vessels or when convergent).Most of the time flow profile is parabolic or displayszones of acceleration near the curvatures (Fig. 2.16)(15). This limits the accuracy of velocity measurements,particularly when integrated into calculations such ascardiac output. Various positioning of the Dopplersample volume in the main pulmonary artery cross sectionalarea, for example, introduces errors of +35% in(A)(B)(C)(D)Figure 2.17 Clinical application of Doppler. A 70-year-old woman before coronary revascularization and aortic valve replacement.(A) The right ventricular hemodynamic pressure waveform is shown with an end-diastolic “A” wave. (B) The trans-tricuspid flow (TTF)Doppler waveform: abnormal E to A ratio with predominant A wave. (C) Doppler hepatic venous flow (HVF): S wave superior to the Dwave. (D) Tissue Doppler interrogation of the tricuspid annulus: abnormal Et to At ratio with predominant At wave. This is consistentwith right ventricular diastolic dysfunction (AR, atrial reversal; Prv, right ventricular pressure; TAV, tricuspid annular velocity).