DK2985_C000 1..28 - AlSharqia Echo Club

Native Aortic Valve 357In those patients, measurement of the vena contractashould be performed perpendicular to the long axis ofthe eccentric jet.(A)ec7. CW Doppler and Pressure Half-TimeThe intensity of the CW Doppler signal is determined bythe number of red blood cells reflecting the incident ultrasoundbeam. Therefore, a very dense regurgitant flowsignal is suggestive of a large regurgitant volume.Severe AR also results in rapid equilibration of pressuresbetween the Ao and the LV. Thus, a rapid decay of theAo 2 LV pressure gradient in diastole is also seen insevere AR. This can be assessed by measurement of theaortic regurgitant flow velocity during diastole, whichreflects the instantaneous pressure gradient between theAo and the LV from the Bernoulli simplified equation.The decay of the Ao 2 LV pressure gradient is estimatedfrom the slope of the aortic regurgitant velocity and theregurgitant pressure half-time (PHT), which is defined asthe time needed for the pressure gradient to fall to halfof its initial value during diastole (Fig. 15.36). From themanipulations shown below, the regurgitant PHT also correspondsto the time needed for the maximum velocity todecrease by 70% of its initial value:Bernoulli equation:P max ¼ 4(V max ) 2P T1=2 ¼ 4(V T1=2 ) 2Regurgitant PHT:P T1=2¼ 1 2 (P max)Therefore:4(V T1=2 ) 2 ¼ 1 2 4(V max) 2VT 2 1=2¼ 1 2 V2 max V T1=2 ¼ V maxpffiffiffi2V T1=2¼ 0:7V maxA deceleration slope .3 m/s 2 or a regurgitant PHT,200 ms suggests either a rapidly decreasing aortic pressureor rapidly increasing LV pressure, both suggestingthe presence of severe AR (Fig. 15.36). The regurgitantPHT should ideally be measured on the slope of beatswith longer duration. From a technical standpoint, theinitial peak velocity represents the pressure gradientbetween the Ao and the LV during early diastole(Fig. 15.35). As this gradient should be at least40 mmHg, an initial peak velocity ,300 cm/sec usuallyindicates improper alignment of the ultrasound beamwith the regurgitant jet.(B)Figure 15.36 (A) Continuous-wave Doppler interrogationacross the regurgitant aortic valve through a transgastricwindow. The regurgitant pressure half-time (PHT) is measuredat 668 ms, consistent with mild regurgitation. (B) The relationshipbetween pressure half-time and blood flow velocity acrossthe aortic valve in diastole is illustrated (DT, deceleration time;Max, maximum; PG, pressure gradient; V max , maximal velocity;Vt 1/2 ¼ velocity at the PHT point).Pitfalls of Pressure Half-TimeSeveral factors must be considered in the interpretationof this quantitative measurement of AR. In certain conditions,a short regurgitant PHT may not necessarily indicatesevere AR: changes in left ventricular compliancewill influence the rate of pressure equilibration betweenthe Ao and the LV. A noncompliant LV is associatedwith a faster left ventricular pressure rise causing asteeper AR slope and shorter regurgitant PHT. Also,patients with chronic AR tend to have a more dilatedand compliant LV which can accommodate a greatervolume of regurgitant blood. Therefore, for the sameregurgitant volume, acute AR will have a steeper ARslope and a shorter regurgitant PHT compared withchronic AR (Fig. 15.37). Other conditions leading to