DK2985_C000 1..28 - AlSharqia Echo Club

338 Transesophageal Echocardiography(A)(B)LVLARVAoFigure 15.12 Transgastric long-axis view at 1308. In this view, the aortic flow is aligned with the Doppler ultrasound beam (Ao, aorta;LA, left atrium; LV, left ventricle; RV, right ventricle).B. Quantitative Assessment of Aortic Stenosis1. Pressure GradientThe Bernoulli EquationThe measured blood flow velocity across cardiac valvescan be converted to a pressure gradient according to theBernoulli equation. This equation takes into accountflow acceleration, viscous friction, and convective accelerationusing a complex mathematical formula. Flowacceleration and viscous friction have little impact onthe pressure gradient and can be ignored in the calculations.Therefore, the modified Bernoulli equation onlyaccounts for convective acceleration. In the modifiedBernoulli equation, the pressure gradient (DP) measuredwith spectral Doppler across the AoV equals four timesthe square of the measured peak velocity (V AoV ) minusthe square of the LVOT velocity.DP ¼ 4 (V 2 AoV V 2 LVOT ) (15:1)In most cases, the square value of the LVOT velocity isinsignificant compared with the maximal aortic velocityand the Bernoulli equation can be simplified to:DP ¼ 4 V 2 AoV (15:2)The ASE task force on Doppler quantificationsrecommends that the simplified Bernoulli equationshould not be used when the LVOT velocity exceeds1.5 m/s (7).Doppler Pressure Gradient vs CardiacCatheterizationDoppler-derived measurements correspond to aninstantaneous gradient while the pull back technique ofthe catheter from the Ao to the left ventricle (LV) duringcardiac catheterization represents a peak-to-peak pressuredifference. This explains in part why the measured peakto-peakgradient in the catheterization laboratory is oftenlower than the instantaneous gradient obtained withDoppler echocardiography. However, the mean pressuregradient correctly measured by simultaneous pressuretracings from the LV and the aortic root during cardiaccatheterization correlates well with the mean gradientobtained with Doppler echocardiography (Fig. 15.20).(A)(B)LVRVLAAoFigure 15.13 Deep transgastric view. Note the parallel alignment of the Doppler ultrasound beam with the aortic flow and the longitudinalimaging of the mitral valve (Ao, aorta; LA, left atrium; LV, left ventricle; RV, right ventricle).