Recommendations for Quantification of Doppler ...color flow Doppler can help determine the direction...

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INTRODUCTION

Doppler echocardiography is a noninvasive tech-nique that provides unique hemodynamic informa-tion otherwise not available without invasive moni-toring.The accuracy of the results depends,however,on meticulous technique and an understanding ofDoppler principles and flow dynamics. This docu-ment provides recommendations based on the sci-entific literature and a consensus from a body ofexperts to guide the recording and measurement ofDoppler data.The document is not a comprehensivereview of all the clinical applications of Dopplerechocardiography.

GENERAL PRINCIPLES

The Doppler principle states that the frequency ofreflected ultrasound is altered by a moving target,such as red blood cells. The magnitude of thisDoppler shift relates to the velocity of the bloodcells, whereas the polarity of the shift reflects thedirection of blood flow toward (positive) or away(negative) from the transducer. The Doppler equa-tion

∆F = �V × 2Fo

c

× cos θ� (1)

states that the Doppler shift (∆F) is directly propor-

tional to the velocity (V) of the moving target (ie,blood cells), the transducer frequency (Fo), and thecosine of the angle of incidence (θ) and is inverselyproportional to the velocity of sound in tissue (c =1540 m/s).The Doppler equation can be solved forblood flow velocity as follows:

V = �2 F

∆

o

F

××co

c

s θ� (2)

When solving the Doppler equation, an angle of inci-dence of 0 or 180 degrees (cosine = 1.0) is assumedfor cardiac applications.

Currently, Doppler echocardiography consists of 3modalities: pulsed wave (PW) Doppler, continuouswave (CW) Doppler, and color Doppler imaging.PWDoppler measures flow velocity within a specificsite (or sample volume) but is limited by the aliasingphenomenon that prevents it from measuring veloc-ities beyond a given threshold (called the Nyquistlimit). CW Doppler, on the other hand, can recordvery high blood flow velocities but cannot localizethe site of origin of these velocities along the path-way of the sound beam. Color flow Doppler usesPW Doppler technology but with the addition ofmultiple gates or regions of interest within the pathof the sound beam. In each of these regions, a flowvelocity estimate is superimposed on the 2-dimen-sional (2D) image with a color scale based on flowdirection, mean velocity, and sometimes velocityvariance.

Doppler echocardiography is used to evaluateblood flow velocity with red blood cells as the mov-ing target. Current ultrasound systems can also applythe Doppler principle to assess velocity within car-diac tissue.The moving target in this case is tissue,such as myocardium, that has higher amplitude ofbackscatter ultrasound and a lower velocity com-pared with red blood cells. This new application is

Reprint requests: American Society of Echocardiography, 1500Sunday Dr, Suite 102, Raleigh, NC 27607. J Am Soc Echocardiogr 2002;15:167-84Copyright © 2002 by the American Society of Echocardiography.0894-7317/2002/$35.00 + 0 27/1/120202doi:10.1067/mje.2002.120202

Recommendations for Quantificationof Doppler Echocardiography:

A Report From the Doppler QuantificationTask Force of the Nomenclature and

Standards Committee of theAmerican Society of Echocardiography

Miguel A. Quiñones, MD, Chair, Catherine M. Otto, MD, Marcus Stoddard, MD,Alan Waggoner, MHS, RDMS, and William A. Zoghbi, MD, Raleigh, North Carolina

AMERICAN SOCIETY OF ECHOCARDIOGRAPHY REPORT

called tissue Doppler and can be performed in thePW or the color mode.A comprehensive discussionof this new technology is beyond the scope of thisdocument; however, some of the newer applicationsfor measuring regional myocardial velocities that usethe PW mode will be discussed.

Doppler echocardiography has 2 uses: detectionand quantitation of normal and disturbed flowvelocities. For detection purposes, all 3 modalitieshave high sensitivity and specificity. However, colorflow Doppler often allows faster detection ofabnormal flows and provides a spatial display ofvelocities in a 2D plane. Quantification of flowvelocity is typically obtained with either PW or CWDoppler. Measuring velocity with color Doppler ispossible, but the methods are still under develop-ment and have not been standardized across differ-ent brands of ultrasound equipment. (One excep-tion is the proximal isovelocity surface accelerationmethod, used in the evaluation of valvular regurgita-tion.) The primary use of PW Doppler is to assessvelocities across normal valves or vessels to evaluatecardiac function or calculate flow. Common appli-cations include measurements of cardiac output(CO) and regurgitant volumes, quantitation ofintracardiac shunts, and evaluation of diastolic func-tion.

CW Doppler,on the other hand, is used to measurehigh velocities across restrictive orifices, such asstenotic or regurgitant valve orifices.These velocitiesare converted into pressure gradients by applyingthe simplified Bernoulli equation:

pressure gradient = 4V2 (3)

This equation has been demonstrated to be accu-rate in flow models, animal studies, and in the car-diac catheterization laboratory as long as the velocityproximal to the obstruction does not exceed 1.5m/s. Common clinical applications include deter-mining pressure gradients in stenotic native valves,estimating pulmonary artery (PA) systolic pressurefrom the velocity of tricuspid regurgitation (TR), anddetermining prosthetic valve gradients. The combi-nation of PW and CW Doppler has been used withgreat accuracy to determine stenotic valve areaswith the continuity equation.

An alternative technique also used for recordinghigh flow velocities is the high pulse repetition fre-quency (PRF) modification of the PW Doppler.HighPRF uses range ambiguity to increase the maximumvelocity that can be detected with PW Doppler.Multiple sample volumes are placed proximal to

Journal of the American Society of Echocardiography168 Quiñones et al February 2002

and at the depth of interest. PRF is determined bythe depth of the most proximal sample volume,which allows measurement of higher velocitieswithout signal aliasing at the depth of interest.Although the resulting spectral output includes fre-quencies from each of the sample volume depths,the origin of the high-velocity signal is inferredfrom other anatomic and physiologic data, as withCW Doppler.

RECOMMENDATIONS ON RECORDING ANDMEASUREMENT TECHNIQUES

The accuracy of measuring blood cell velocities byDoppler relies on maintaining a parallel orientationbetween the sound waves and blood flow.Although most ultrasound systems allow correc-tion of the Doppler equation for the angle of inci-dence, this measurement is difficult to performaccurately because of the 3-dimensional orienta-tion of the blood flow. Angle correction is there-fore not recommended. The Doppler sound beamshould be oriented as parallel as possible to theflow, guided both by the 2D image (sometimesassisted by color flow imaging) and the quality ofthe Doppler recording. Small (<20 degrees) devia-tions in angle produce mild (<10%) errors in veloc-ity measurements. Although these errors may beacceptable for low-velocity flows, when Doppler isused to derive pressure gradients even a smallerror in velocity measurement can lead to signifi-cant underestimation of the gradient because ofthe quadratic relation between velocity and pres-sure gradient.

PW Doppler

PW Doppler is used in combination with the 2Dimage to record flow velocities within discreteregions of the heart and great vessels. Measurementsderived from these velocities are used to evaluatecardiac performance (Figure 1). The most commonsites are the left ventricular outflow tract (LVOT),mitral annulus and left ventricular inflow (at the tipsof the mitral valve leaflets), pulmonic valve annulusand PA, tricuspid valve inflow, hepatic veins, and pul-monary veins. The flow volume passing throughthese sites can be calculated as the product of thevelocity-time integral (VTI) and the cross-sectionalarea (CSA) of the respective site. When recordingvelocities for flow measurements, the sample vol-ume is placed at the same location as the 2D mea-surements of CSA. Adjust the sample volume axial

Journal of the American Society of EchocardiographyVolume 15 Number 2 Quiñones et al 169

length to 5 to 7 mm and set the wall filters at low lev-els to ensure that lower velocities adjacent to thebaseline are recorded for the timing of flow to bemeasured correctly.The velocities should be record-ed over at least 2 or 3 respiratory cycles at a paper orsweep speed of 50 or 100 mm/s; the faster speed isessential for measurements that require precise timeresolution,such as time intervals, integrals,and veloc-ity slopes.

A typical PW Doppler velocity consists of a spec-tral recording of varying intensity, depending on theacoustic density of the reflected interface, ie, themass of blood cells (Figure 1). The most dense (orbrightest) portion of the spectral tracing representsthe velocity of the majority of blood cells, alsoknown as the modal velocity. Likewise, less denseareas depict the velocity of a lesser mass of bloodcells.When measuring velocities, use the outer edgeof the dense (or bright) envelope of the spectralrecording.

CW Doppler

In contrast to PW Doppler, CW Doppler records thevelocities of all the red blood cells moving along thepath of the sound beam (Figure 2). Consequently, aCW Doppler recording always consists of a full spec-tral envelope with the outer border correspondingto the fastest moving blood cells. No simple guide-lines guarantee a parallel orientation of the CWbeam with blood flow in all instances. However,color flow Doppler can help determine the direction

of the jet in a 2D plane, particularly in regurgitantlesions. A nonimaging CW transducer is recom-mended to search for the highest velocity, particular-ly in aortic stenosis (AS), in which multiple windowsof examination may be required to detect the high-est velocity. Measurements of velocities recorded byCW Doppler are always taken from the outer border.The site of origin of a high-velocity jet is inferredfrom the particular lesion that is being examined.Forinstance, if the CW beam is directed through astenotic aortic valve, the outer edge of the recordingis assumed to represent the stenotic jet velocity.Therefore, only well-defined envelopes should beused for quantitation of velocities to obviate signifi-cant errors.These recommendations are also appliedwhen high PRF is used to record a high-velocity jet,except that high PRF should be used in combinationwith the 2D image.

Color Flow Doppler

A comprehensive discussion of color flow Doppleris beyond the scope of this document. Nevertheless,the following are some basic recommendations thatapply to any ultrasound machine. Processing themultigate Doppler information and creating thecolor pixels take a certain amount of time; thereforethe larger the area of interest, the slower the framerate. For this reason, a smaller area of interest shouldbe used and depth settings kept at the lowest possi-

Figure 1 PW Doppler recording of left ventricular outflowtrack velocity obtained from apical window. Because flowis away from transducer, velocities are displayed belowbaseline. Notice narrow spectral pattern during flow accel-eration and deceleration and wider dispersion seen duringmid-systole. Degree of dispersion indicates range of bloodflow velocities detected within sample volume.

Figure 2 CW Doppler recording of velocity through aor-tic valve in patient with AS. Transducer position is at apex;thus systolic velocities are displayed below baseline. Indiastole, positive mitral inflow velocities can be seen asinflow moves toward transducer. Note wide spectral dis-persion of velocities during systole and diastole indicatingthat Doppler beam is detecting all flow velocities encoun-tered along its course.

ble level that allows visualization of the structure inquestion. When high-velocity blood flows are ana-lyzed,set the color scale at the maximum allowed forthat given depth. Color Doppler gain should be setjust below the threshold for noise.

RECOMMENDATIONS RELATING TO SPECIFICCLINICAL USES

Flow Measurements

PW Doppler technique. Flow is derived as theproduct of CSA and the average velocity of theblood cells passing through the blood vessel orvalve orifice during the flow period (Figure 3),whereas stroke volume (SV) represents the productof CSA and VTI. When PW Doppler is used, thevelocities recorded within the sample volume willbe affected by the flow profile.With current instru-mentation, assessing flow profile or measuring theaverage velocity of the blood cells is difficult.Consequently, volume-flow measurements are mostaccurate when flow is laminar (ie, all blood cells aremoving in the same direction) and the profile is flat.The most important technical factor to ensure accu-


racy of measurements is to properly match the siteof velocity recording with the anatomic measure-ment of the CSA.1 For this reason, it is preferable touse sites where the CSA does not change signifi-cantly during the flow period and can be deter-mined accurately from the 2D image and where theflow profile is likely to be flat. When tracing thevelocity to derive a VTI, it is best to trace the outeredge of the most dense (or brightest) portion of thespectral tracing (ie, the modal velocity) and ignorethe dispersion that occurs near peak velocity. Forpatients in sinus rhythm, data from 3 to 5 cardiaccycles may be averaged. However, in patients withirregular rhythms such as atrial fibrillation, 5 to 10cycles may be required to ensure accuracy ofresults.

The preferred sites for determining SV and cardiacoutput (in descending order of preference) are as fol-lows:

1. The LVOT tract or aortic annulus2. The mitral annulus3. The pulmonic annulus

The LVOT is the most widely used site.2 SV is derivedas:

SV = CSA × VTI (4)

The CSA of the aortic annulus is circular, with littlevariability during systole. Because the area of a circle= πr2, the area of the aortic annulus is derived fromthe annulus diameter (D) measured in the paraster-nal long-axis view as:

CSA = D2 × π/4 = D2 × 0.785 (5)

Image the LV outflow with the expanded or zoom

Figure 3 Diagrammatic illustration of flow through a ves-sel showing 2 different flow profiles. Flat profile with allcells traveling at same velocity and parabolic profile withcells at center traveling faster than those on the side. At anygiven time, flow through the vessel represents product ofaverage velocity of all cells multiplied by CSA of the vessel.

Figure 4 Method used in determining systolic flow vol-ume through left ventricular outflow.


option and place 1 or 2 beats in a cineloop (Figure4).This imaging allows a more precise measurementof the annulus diameter during early systole from thejunction of the aortic leaflets with the septal endo-cardium, to the junction of the leaflet with the mitralvalve posteriorly, using inner edge to inner edge.Thelargest of 3 to 5 measurements should be takenbecause the inherent error of the tomographic planeis to underestimate the annulus diameter.When seri-al measurements of SV and CO are being performed,use the baseline annulus measurement for therepeated studies because little change in annulussize occurs in adults over time.

The LV outflow velocity is recorded from the api-cal 5-chamber or long-axis view, with the samplevolume positioned about 5 mm proximal to the aor-tic valve (Figure 4).The opening click of the aorticvalve or spectral broadening of the signal should notbe viewed in mid-systole because this means thesample volume is into the region of proximal accel-eration.The closing click of the aortic valve is oftenseen when the sample volume is correctly posi-tioned.

The LVOT method should not be applied whenthe landmarks needed to measure the annulus diam-eter cannot be properly visualized or if evidence ofLV outflow obstruction exists because the velocitiesrecorded will not be matched to the CSA of the aor-tic annulus.

Flow across the mitral annulus is measured inthe apical 4-chamber view with equation 4 (Figure

5).Although the mitral annulus is not perfectly cir-cular, applying a circular geometry (equation 5)gives similar or better results than attempting toderive an elliptical CSA with measurements takenfrom multiple views.2,3 The diameter of the mitralannulus should be measured from the base of theposterior and anterior leaflets during early to mid-diastole, 1 frame after the leaflets begin to closeafter its initial opening.The sample volume is posi-tioned so that in diastole it is at the level of theannulus.

The pulmonic annulus is probably the most diffi-cult of the 3 sites, mostly because the poor visualiza-tion of the annulus diameter limits its accuracy andthe right ventricular (RV) outflow tract contractsduring systole. Measure the annulus during earlyejection (2 to 3 frames after the R wave on the elec-trocardiogram) from the anterior corner to the junc-tion of the posterior pulmonic leaflet with the aorticroot (Figure 6).4,5 Equations 4 and 5 are used toderive SV and CSA, respectively.

When learning to measure flow volumes acrossthe above sites, make measurements in all 3 sites inpatients without regurgitant lesions or intracardiacshunts because the flow through these sites shouldbe equal. Doing this will develop expertise neededto apply these methods accurately. In regurgitantvalve lesions, the forward flow through the regur-gitant valve is greater than through the othervalves, and the difference between them is equiva-lent to the regurgitant flow. Regurgitant fraction,an index of severity of regurgitation, is derived asregurgitant flow (in milliliters) divided by the for-ward flow across the regurgitant valve. In the pres-ence of significant left-to-right intracardiac shunts,flow measurements can calculate the pulmonic tosystemic (Qp:Qs) f low ratio. For example, in a

Figure 5 Method used in determining diastolic flow vol-ume through mitral annulus.

Figure 6 Method used in determining systolic flow vol-ume through pulmonic annulus.

patient with an atrial-septal defect, pulmonic flowwill be much higher than aortic flow; the ratio ofthe two is equivalent to the Qp:Qs ratio. In the bestof hands, these calculations may have up to a 20%error.

Flow measurements with CW Doppler. Recordingsof flow velocity through the above sites are also pos-sible with CW Doppler. In addition, flow velocity canbe recorded in the ascending aorta from the supra-sternal notch.6 The main difficulty with CW Doppleris that the velocity envelope reflects the highestvelocity of the moving blood cells. This, in turn, isaffected by the flow profile and the smallest CSA offlow. For example, when recording the LV outflowvelocity from the apical window by CW, the velocityintegral is related to the CSA of the aortic valverather than the annulus.7 The area of the valve ismore difficult to derive with 2D imaging.

A primary application of Doppler is in the serialevaluation of SV and CO. Given that the CSA is rela-tively stable in the same patient, the VTI can accu-rately track changes in SV. The day-to-day variabilityof velocity measurements appears to be less withCW than with PW Doppler.8

Application of Flow Measurements in theEvaluation of Diastolic Function

Left ventricle. PW Doppler recordings of themitral and pulmonary vein velocities can provideinsight into the dynamics of LV filling and help eval-uate diastolic function (Figure 7).9-11 Importantly,


changes in these velocities occur with alterations inleft atrial and LV diastolic pressures.12-18 In addition,the transmitral velocity, together with tricuspid andhepatic vein velocities, is useful when evaluating car-diac tamponade and constrictive pericarditis.19-23

Mitral inflow velocity. Parameters of diastolicfunction that reflect changes in flow should be mea-sured from recordings of the inflow velocity at themitral annulus,where the CSA is more stable.On theother hand, parameters that relate to the transmitralgradient are best obtained at the tips of the valveleaflets. The measurements obtained are dividedinto 3 categories: (1) absolute velocities such as Eand A velocities, (2) time intervals such as accelera-tion and deceleration times, and (3) time-velocityintegrals such as the integrals of the E and A veloci-ties, respectively.The ratio of these integrals to thetotal integral of flow velocity is used as an index ofthe respective filling fractions.The first 2 categoriesare best measured at the tips of the valve leaflets,whereas the third is more accurate from the mitralannulus site.

An additional index of diastolic function is the iso-volumic relaxation time (IVRT), defined as the inter-val from the closure of the aortic valve to the open-ing of the mitral valve. This interval can beaccurately measured by Doppler with either PW orCW Doppler. With PW Doppler, the transducer isangulated into the apical 5-chamber or long-axisview and the sample volume placed within theLVOT, but in proximity to the anterior mitral valve(MV) leaflet to record both inflow and outflow sig-

Figure 7 Example of transmitral and pulmonary veinvelocity recordings in a healthy subject. Pulmonary veinvelocity recording has been aligned in time with mitralvelocity for illustration purposes.

Figure 8 Method used for measuring IVRT from record-ing of LV outflow and inflow velocities with CW Doppler.Transducer is at cardiac apex, and Doppler cursor isaligned in intermediate position between aortic and mitralvalves.


nals.With CW Doppler, IVRT is measured by aimingthe Doppler beam at an intermediate positionbetween inflow and outflow to record both veloci-ties (Figure 8). IVRT is measured as the intervalbetween the end of ejection and the onset of mitralinflow. As a rule, CW recordings provide a morereproducible measure of IVRT than PW. Three to 5cardiac cycles should be averaged when measuringtransmitral velocities and IVRT. One exception tothis rule is made in conditions in which these veloc-ities change with respiration, such as in pericardialconstriction or tamponade. In these cases, the veloc-ities should be recorded with a respiratory tracingand averaged separately.

Certain patterns have been associated withchanges in left atrial pressures in patients with LVdisease, particularly those with depressed systolicfunction (Figure 9). With normal pressures, thetransmitral velocity, as a rule, has a lower E than Avelocity with a prolonged IVRT and decelerationtime, reflecting the impaired relaxation of the leftventricle. On the other hand, with higher left atrialpressures, the E velocity increases whereas the IVRTand deceleration time shorten. This resembles thepattern seen in healthy young persons and thus it isreferred to as pseudonormal.

Pulmonary vein velocity. Analysis of the pul-monary vein velocities can provide insight into thediastolic properties of the LV and the function of theleft atrium. Certain patterns have been associatedwith increased left atrial pressures in patients with

LV disease, particularly those with depressed sys-tolic function, that complement the informationderived from the mitral inflow velocity (Figure9).16,17 With current technology, the velocity of flowwithin the pulmonary veins can be recorded fromthe transthoracic apical view in 80% of patients.Themost common vein accessible from this window isthe right upper pulmonary vein.The flow within thevein can be visualized with color Doppler using alower velocity scale (<40 cm/s) and the PW samplevolume can be placed inside the vein.Without atten-tion to proper sample volume location, 2 errorscommonly occur.The sample volume can be placednear the opening of the pulmonary vein but stillwithin the left atrium, or the low-velocity motion ofthe posterior atrial wall can be recorded. Whenrecording the pulmonary veins, keep the wall filtersat a low level.

The flow velocity measurements currently recom-mended in the pulmonary veins are the peak systolic(S), peak diastolic (D), and atrial reversal (A) veloci-ties, the S/D ratio, and the duration of the A velocity(Figures 7 and 9).

Myocardial and annular velocities. Longitudinalvelocities within the myocardium can be recordedwith tissue Doppler from the apical window withthe PW mode. A small (<5 mm) sample volume isplaced within a myocardial segment and a spectralrecording of velocities within the segment obtained(Figure 10). For optimal recording of tissue velocity,both gains and filter settings should be set low.

Figure 9 Diagrammatic illustration of 3 common patternsof mitral and pulmonary vein velocities: normal, delayedrelaxation, and pseudonormal.

Figure 10 Myocardial velocity recording obtained fromapical window with tissue Doppler using PW mode.Diagram illustrates Doppler cursor with sample volumepositioned at base of lateral wall. Recording shows systolicpositive wave (S), early diastolic wave (Em), and atrial wave(Am).

Myocardial velocities are highest at the base and low-est toward the apex. Consequently, the velocities atthe basilar segments are commonly used to assessthe function of the corresponding wall.The samplevolume is usually placed at the junction of the LVwall with the mitral annulus.

The spectral longitudinal velocity of the myocardi-um normally consists of a positive systolic wave and2 diastolic peaks, one during early diastole and a sec-ond during atrial contraction (Figure 10). The earlydiastolic velocity (Em; also referred to as Ea for annu-lar velocity) has been demonstrated to be an index ofLV relaxation that is relatively insensitive to left atri-al pressure.24-26 Although Em can be measured in anyventricular wall, the lateral wall and septum havebeen more commonly used in the evaluation of dias-tolic function. The ratio of transmitral E velocity toEm has been recently demonstrated to relate wellwith mean left atrial (or pulmonary capillary wedge)pressure in multiple clinical scenarios, such asdepressed or normal systolic LV function, hyper-trophic cardiomyopathy, sinus tachycardia, and atrialfibrillation.26-30

Flow propagation velocity. Color Doppler canrecord an early inflow velocity across the MV fromthe apical 4-chamber view (Figure 11). An M-modecursor placed in the center of the brightest inflowvelocity can record a color M-mode of the inflow jet


as it moves from the mitral inflow area toward theapex.Adjusting the color Doppler baseline can high-light a color edge, the slope of which represents thepropagation velocity of blood flowing toward theapex.This flow propagation velocity has been shownto relate inversely with the time constant of LV relax-ation and to be fairly insensitive to changes in leftatrial pressures.31,32 In a manner analogous to the Emvelocity, the ratio of transmitral E to flow propaga-tion velocity relates to mean left atrial (or pulmonarycapillary wedge) pressure.33,34

Right ventricleTricuspid inflow velocity. As with the mitral

inflow, the tricuspid inflow velocity reflects the atri-oventricular diastolic pressure-flow interactions onthe right side of the heart.Tricuspid flow velocities,however, are also affected by respiration; thus allmeasurements taken must be averaged throughoutthe respiratory cycle or recorded at end-expiratoryapnea.The tricuspid inflow velocity is best recordedfrom either a low parasternal RV inflow view or fromthe apical 4-chamber view.

The same measurements derived from the mitralinflow velocity can be measured in the tricuspid.

Figure 11 Demonstration of method used to measureflow propagation velocity using color M-mode. In panelA, 2D color Doppler frame with M-mode cursor alignedin center of red inflow velocities is shown. Panels B and Cillustrate color M-mode tracing obtained through cursorat 2 different aliasing velocities obtained by shifting 0baseline. This maneuver enhances appreciation of thepropagation velocity.

Figure 12 Normal hepatic vein velocity recorded fromsubcostal window. From this window, a negative velocityindicates antegrade flow moving toward RA. Notice thatantegrade systolic velocity is larger than antegrade diastolicvelocity. Small retrograde atrial (A) velocity is also seen.These velocities are subject to variation with respiration.


However, to date, there are fewer investigations avail-able on the application of these measurements in theevaluation of RV diastolic function. RV IVRT has notbeen used as an index of diastolic function becauseit is significantly altered by pulmonary hypertensionand difficult to measure with Doppler alone.

Hepatic vein flow velocity. The velocity of flow inthe hepatic veins can be recorded from the subcostalwindow with the flow oriented parallel to the soundwaves (Figure 12).The normal pattern of flow veloc-ity consists of systolic and diastolic antegrade flowvelocities (S and D waves, respectively) and a retro-grade A velocity. Each of these waves being pro-foundly altered by the 2 phases of respiration. Theinfluence of respiration differs between diseasestates.These variations may be used to differentiatebetween restrictive and constrictive pericardial dis-orders.22

Estimation of Right-sided Pressures

When TR is present, application of the 4V2 equationto the peak TR velocity provides a close estimate ofthe peak pressure gradient between RV and rightatrium (RA).35 Consequently, RV systolic pressurecan be derived by adding an estimate of mean RApressure to the peak RV-RA gradient. The mean RApressure is estimated with the magnitude of the infe-rior vena cava collapse, with inspiration and varia-tions in the hepatic vein velocities.36-38 In theabsence of pulmonic stenosis, the peak RV pressureis equivalent to the PA systolic pressure. In the pres-ence of pulmonic stenosis, the PA systolic pressure isestimated by subtracting the maximal pulmonicvalve pressure gradient, derived from the velocityacross the valve by CW Doppler, from the peak RVsystolic pressure.The accuracy of these pressure esti-mates depends on recording a clear envelope of theTR velocity by CW Doppler. If the signal is incom-plete, significant underestimation of the peak TRvelocity will occur. The quality of the TR velocityrecording may be enhanced with contrast echocar-diography by injecting agitated saline solution orother contrast echocardiographic agents intra-venously.39

Varying degrees of pulmonic regurgitation (PR)are common, particularly in cardiac patients. Thevelocity of PR reflects the instantaneous gradientbetween PA and RV.Thus, the PR velocity at end-dias-tole may be used to derive the PA diastolic pressurewith the 4V2 equation and adding to the pressuregradient an estimate of mean RA pressure.

The RV outflow and pulmonic flow velocities areoften altered in the presence of significant pul-

monary hypertension.The acceleration time is short-ened, and a mid-systolic notch in the flow velocityenvelope is often present.An inverse curvilinear rela-tion exists between the acceleration time and meanPA pressure from which regression equations havebeen developed. The 95% confidence limits of theestimate of PA pressure with these equations are,however, too wide for accurate clinical use and aretherefore not recommended.

Pressure Gradients and Valve Areas

Recommendations on the use of CW Doppler forrecording high-velocity jets have been previously dis-cussed.The modified Bernoulli equation, 4V2, is veryaccurate in estimating the pressure gradient across arestrictive orifice under most physiologic condi-tions.40-43 The exceptions are as follows: (1) a veloci-ty proximal to the stenosis greater than 1.5 m/s; (2)the presence of 2 stenotic areas proximal to eachother, for example, subpulmonic stenosis combinedwith valvular stenosis; and (3) the presence of a longtunnel-like stenotic lesion.

In stenotic lesions, the jet velocity can derive the

Figure 13 Diagrammatic representation of continuityequation. When laminar flow encounters a small discretestenosis, it must accelerate rapidly to pass through smallorifice. Flow proximal to stenosis is same as flow passingthrough stenosis. Because flow equals velocity times CSA,area of stenotic orifice can be solved if velocity throughorifice and flow is known.

peak instantaneous and the mean pressure gradientacross the stenosis. The mean gradient is obtainedby averaging the instantaneous gradients. Currentultrasound systems contain software to derive thepeak velocity, VTI, and mean gradients from a trac-ing of the velocity envelope. It is important toinclude both heart rate and rhythm when reportingvalve gradients.The Doppler equation is fairly accu-rate in deriving the pressure gradient across a tightstenosis. However, in AS the phenomenon of pres-sure recovery may result in a higher gradient byDoppler than the gradient measured by catheter,particularly if the distal pressure is recorded sever-al centimeters away from the stenotic valve. In prac-tice, the error is small and of minimal clinical sig-nificance.

Valve area measurements with the continuityequation. The continuity equation states that theflow passing through a stenotic valve is equal to theflow proximal to the stenosis (Figure 13). Given thatflow equals velocity multiplied by CSA, if flow isknown the area of stenosis can be derived as:

Stenotic area = Flow/Velocity across stenosis (6)

AS is the most common lesion for which the con-tinuity equation is used.4,44,45 The flow volume rep-resents the SV across the aortic valve, determined atthe LV outflow. In AS, however, the sample volumemust be positioned carefully to not be within theprestenotic flow acceleration region. Place the sam-ple volume 1 cm proximal to the aortic valve whilerecording the velocity.Then, slowly move the sample


volume toward the valve until an increase in veloci-ty and spectral broadening is seen. Thereafter, thesample volume is moved back until a narrow band offlow velocities is obtained.The denominator of thecontinuity equation is the integral of the stenotic jet.Consequently, the maximal AS velocity must berecorded by aligning the CW beam as parallel as pos-sible to the stenotic jet. This is best accomplishedwith a nonimaging CW transducer that uses multiplewindows of interrogation.

In mitral stenosis, the continuity equation is usefulin situations for which the pressure half-timemethod is limited. However, in this lesion accuratelydetermining flow across the mitral annulus is diffi-cult. SV is therefore measured at the aortic annulusand used in the numerator of the equation; thedenominator is the integral of the mitral stenosis jet.The method is quite accurate in the absence of asso-ciated mitral regurgitation (MR).5

Mitral valve area with the pressure half-timemethod. The pressure half-time (P1/2t) method is asimple and accurate method of determining valvearea in mitral stenosis (Figure 14). Pressure half-timerepresents the time that the maximal pressure gradi-ent takes to decrease by one half.When expressed interms of velocity, this time is equivalent to the timethat the peak stenotic velocity takes to drop by 30%.Early studies established an inverse relation betweenP1/2t and mitral valve area (MVA),46 and from thisrelation the following empirical equation wasderived:

MVA = 220/P1/2t (7)

Figure 14 CW Doppler tracing taken from a patient withmitral stenosis, illustrating measurement of pressure halftime.

Figure 15 CW Doppler recording of transmitral velocityin a patient with mitral stenosis. Velocity pattern showsrapid early deceleration that decelerates to mid-diastole,giving rise to “ski slope” appearance. In these cases, esti-mating pressure half time from the slower component ofvelocity descent is better, as illustrated in second cardiaccycle.


This formula works surprisingly well in mostpatients and can be reliably used in clinical decisionmaking.47,48 Potential sources of errors must beconsidered, such as rapid heart rate, the presence ofsignificant aortic regurgitation, and conditions thatalter left atrial or LV compliance and/or LV relax-ation.49-51 In some patients, the early velocitydescent is curvilinear rather than linear, resemblinga ski slope. In these instances, derive a pressure halftime by extrapolating the mid-diastolic lineardescent backward, as illustrated in Figure 15.Although there are similarities between mitral andtricuspid stenosis, the P1/2t method has not been asextensively validated for the calculation of tricuspidvalve area.

Application of Doppler in Regurgitant ValveLesions

Doppler echocardiography is the most commonlyused diagnostic technique for detecting and evaluat-ing valvular regurgitation. Multiple indexes havebeen developed to assess severity of regurgitationwith PW, CW, and color Doppler. Although tech-niques for measuring these indexes are described inthis document, recommendations concerning theirclinical application will be discussed in an upcomingdocument dedicated to the evaluation of regurgitantvalve lesions.

Regurgitant volume, regurgitant fraction, andeffective regurgitant orifice area. In the presence ofvalvular regurgitation, the flow through the affectedvalve is greater than through other competentvalves. For example, in MR more volume will passthrough the MV than through the aortic or pulmonic

valves. The difference between the two representsthe regurgitant volume. Regurgitant fraction isderived from the regurgitant volume divided by theflow through the regurgitant valve.3,52 Careful mea-surement of flow volumes through the annular sitesdescribed can determine the calculation of regurgi-tant volume and regurgitant fraction.

Effective regurgitant orifice area (EROA) is a newindex of regurgitation derived with the continuityequation:

EORA = Regurgitant volume/Regurgitant VTI (8)

where the regurgitant VTI is the integral of the regur-gitant velocity recorded by CW Doppler.53

Application of pressure half time in aortic regur-gitation. Recording of aortic regurgitation jet by CWDoppler reflects the instantaneous pressure differ-ential between the aorta and left ventricle.Thus, therate of velocity decline from its early peak to latediastole is an index of severity of aortic regurgita-tion.Although this rate of decline may be measuredas a slope, it is more commonly assessed by measur-ing pressure half time in a manner analogous tomitral stenosis; that is, the time taken for the peakvelocity to decline by 30% (Figure 16).54 To accu-

Figure 16 CW Doppler tracing of aortic regurgitationvelocity illustrating method for determining pressure halftime.

Figure 17 Diagrammatic illustration explaining concept ofentrainment. Flow is passing from chamber A to chamberB through discrete stenosis that generates high-velocityjet. Initial high-velocity jet is depicted in black. As high-velocity flow enters receiving chamber, blood that sits inthat chamber is forced into motion. Blood cells will movein a circular fashion around high-velocity jet and will beencoded by color Doppler. Jet in receiving chamberbecomes wider. In case of mitral valve regurgitation, thisphenomenon will make regurgitant jet area appear largerthan expected for a given volume of regurgitation.

rately measure this index, a complete envelope ofthe regurgitant jet must be recorded by CW and thepeak velocity should be 4 m/s or greater. In additionto the severity of regurgitation, other hemodynamicfactors such as LV diastolic compliance and systemicvascular resistance can alter the rate of decline of theregurgitant velocity.

Application of color flow Doppler. Color flowDoppler imaging is widely used to detect regurgitantvalve lesions.The area of color Doppler flow velocitydisturbance in the receiving chamber provides asemiquantitative evaluation of regurgitant severity.Trivial and mild degrees of regurgitation, as a rule,have thin jets that travel short distances into thereceiving chamber; more severe lesions have broaderjets covering larger areas within the receiving cham-ber. However, the regurgitant jet area is seriously lim-ited by numerous technical and physiologic vari-ables that affect the length and width of theregurgitant jet. Jets that are centrally directed into areceiving chamber tend to have a larger color jetarea for a given flow because of entrainment ofblood cells inside the receiving chamber (Figure17). On the other hand, eccentric jets travelingalong a wall will lose energy and have a smallercolor area for a given flow.55 Regurgitant jet areashould therefore be used with caution when assess-ing severity of regurgitant lesions. Furthermore,when assessing valve regurgitation, set the aliasingthreshold in the color scale to the highest possiblelevel to limit the effect of entrainment on the regur-gitant jet area.

Parameters derived from the color flow velocitieswithin the regurgitant orifice appear to be moreaccurate than the color jet area in evaluating severi-ty of regurgitation.56-58 To assess these parameters


well, image the regurgitant site in multiple longitu-dinal and cross-sectional planes, paying meticulousattention to imaging the velocities within the regur-gitant orifice. Both the width and the area of theregurgitant jet at the valve orifice (ie, near the venacontracta) or immediately distal to the orifice relatewell with other independent measurements ofseverity of regurgitation (Figure 18).56-58

Examination of the flow velocity pattern proximalto the regurgitant orifice provides insight into theseverity of regurgitation. Proximal flow accelerationoccurs with the isovelocity “surfaces” assuming ahemispheric shape adjacent to the regurgitant ori-fice that can be visualized with color Doppler(Figure 19).59-62 The velocity in this proximal isove-locity surface area (PISA) is equal to the aliasingvelocity (Va). Regurgitant flow (in milliliters per sec-ond) can be derived from the PISA radius (r) as 2πr2

× Va. Assuming the maximal PISA radius occurssimultaneously with the peak regurgitant flow andthe peak regurgitant velocity (PkVreg), the EORA isderived as:

EORA = (2πr2 × Va)/PkVreg (9)

Regurgitant volume can be estimated as EORAmultiplied by regurgitant VTI.63

The above calculations can be accurately per-formed only if the region of PISA appears hemi-spheric. To ensure this, the sound waves should beoriented parallel to flow and the color Doppler base-line shifted toward the direction of regurgitant flow

Figure 18 Color Doppler recording of MR in parasternallong-axis (left) and short-axis (right) view. Measurementof jet height and width is illustrated by arrows.

Figure 19 Diagrammatic representation of concept ofPISA used to assess severity of MR.


until a semicircular area of PISA is well visualized.This method is therefore easier to apply to regurgi-tant lesions involving the MV, particularly those withcentrally directed jets.

Evaluating Prosthetic Valves

The general principles for evaluating prostheticvalve function are similar to those of native valvestenosis. Because a prosthetic valve in general has asmaller effective area than the corresponding normalnative valve,higher velocities, and therefore pressuregradients, are recorded through the prosthesis com-pared with a native valve. Velocities and gradientsthrough prosthetic valves depend on valve type andsize, flow, and heart rate.64,65 Thus, reporting heartrate in addition to other parameters should be partof the routine assessment of prosthetic valve func-tion. Overall, pressure gradients by Doppler and bycatheter measurements correlate well.66 However, incertain valve prostheses, specifically bileaflet valves,overestimation of gradients by Doppler has beendemonstrated, particularly for smaller sized prosthe-ses.67,68

The technique of recording adequate velocitiesthrough prosthetic valves is similar to that of nativevalves, with special attention directed toward mini-mizing the angle of incidence between the Dopplerbeam and flow velocity. For prostheses in the mitralor tricuspid position, this is performed from the api-cal or low parasternal window and can be guidedwith color flow imaging. However, some cases,because of an unusual position of the valve or pres-ence of obstruction, have an eccentric inflow jet (orjets). In these cases the window of examinationshould be modified accordingly. For aortic valveprostheses, recording from all available windows,including apical, right sternal border, suprasternal,and subcostal, is encouraged to avoid an error inflow angulation and underestimation of gradients.This recording is particularly important in stenoticprosthetic valves, for which the stenotic jet may beeccentric, similar to native AS.

Prosthetic aortic valve function. Because gradientsdepend on flow (among other factors), the continuityequation is also applied to prosthetic valves.For pros-thetic aortic valves, measurement of flow is usuallyperformed with the apical 5-chamber or long-axisview,with the sample volume positioned within 1 cmproximal to the valve. By the continuity equation,effective aortic valve area can be derived as SV divid-ed by the time-velocity integral of the jet. For deter-mination of SV,measure the diameter of the LVOT;butin difficult cases, the sewing ring diameter can be

substituted for the LVOT diameter, recognizing that itmay yield a higher value for the effective valvearea.65,69

Doppler-derived effective valve areas have beenshown to relate to valve size and have been report-ed for few prostheses. A Doppler velocity index,derived as the ratio of peak velocity in the LVOT tothe peak velocity through the prosthesis, is lessdependent on valve size.This index is especially use-ful if the valve size is not known at the time of thestudy 65,68

Prosthetic mitral and tricuspid valve function.Mean gradients for several types of mitral prosthe-ses and more recently for tricuspid prostheses, havebeen reported. Effective valve area has beenderived for prosthetic MVs with the P1/2t formula.However, the constant of 220 has been derived fornative MVs, not for prosthetic MVs.70 As with nativevalves, the P1/2t method has limitations similar tothose previously discussed but is useful in detect-ing prosthetic valve obstruction.71 In cases inwhich discordance between gradients and effectivearea is apparent, application of the continuity equa-tion may be beneficial.72 No data are available forthe application of the continuity equation in tricus-pid valves.

Prosthetic valve regurgitation. For the most part,all the currently used mechanical valves have a min-imal degree of functional (“built-in”) regurgitationthat, at times, is detected with Doppler ultrasoundand should not be confused with pathologic regur-gitation.73,74 Regurgitation of prosthetic aorticvalves is readily detected by transthoracic Dopplerechocardiography, and its severity is assessed by sev-eral modalities in a manner analogous to native aor-tic insufficiency. Because of the position of the pros-thetic MV in relation to the transducer and theregurgitant chamber, considerable ultrasound shad-owing and Doppler flow masking occurs duringtransthoracic studies in these patients.This scenariois more severe in mechanical valves compared withbioprosthetic valves. Thus, transthoracic color andconventional Doppler are less sensitive for the detec-tion of prosthetic MV regurgitation.75,76 A nonimag-ing CW transducer should be used in all patientswith prosthetic MVs because the lower frequencysound wave has better penetration and can oftenrecord a regurgitant jet that has not been detectedwith the imaging transducer. In patients with amechanical St. Jude’s mitral prosthesis, a peak earlyvelocity of 1.9 m/s or greater without other signs ofobstruction is 90% sensitive and 89% specific for sig-nificant valve regurgitation.77 Transesophageal echo-

cardiography is often needed to confirm this lesionand assess the severity of regurgitation. For the mostpart, prosthetic tricuspid valve regurgitation is easierto detect than MR.

SUMMARY AND CONCLUSIONS

Doppler echocardiography provides an accurateassessment of the severity of many cardiac disordersand has therefore assumed an integral role in theclinical evaluation of cardiac patients.This documentemphasizes the appropriate methods to properlyrecord and quantify Doppler velocities. However,expertise in the performance of Doppler echocar-diography can only be obtained by appropriate train-ing, practice, and experience. Lastly, the field ofechocardiography is dynamic and continues toevolve rapidly. Therefore, future modifications ofthese recommendations will be created as newermethods and applications of Doppler echocardiogra-phy emerge.

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GLOSSARY OF TERMS

Aliasing: Ambiguous frequencies (or velocities)caused by frequencies exceeding the PRF sampling(Nyquist) limit with PW Doppler.The high velocities“wrap around” and are displayed as negative veloci-ties.

Amplitude: The intensity of the backscatterechoes reflected off the moving blood cells and dis-played in gray scale. It reflects the number of redblood cells moving at a given velocity in a giventime.

Baseline shift: Repositioning of the zero flowvelocity line to the forward or reversed channels toovercome aliasing.Also referred as zero shift.

Bernoulli Equation:An equation that relates theinstantaneous pressure drop across a discrete steno-


sis to convective acceleration, viscous forces, andearly phasic acceleration.The latter 2 factors are usu-ally neglected in the “modified” equation (4V2).

Carrier frequency:The frequency emitted by thetransducer.

Continuity equation: Principle of the conserva-tion of mass in which the flow volume proximally toa valve equals the distal flow volume. Because flow =area (A) × velocity (V), it follows that A1 × V1 = A2 ×V2.

Continuous wave (CW) Doppler:A method tomeasure Doppler velocity with a transducer incor-porating 2 ultrasound crystals (or array of crystals).One constantly transmits a selected ultrasound fre-quency, and the other constantly receives frequen-cy shifts backscattered from red blood cells inmotion. High-flow velocities can be recorded with-out aliasing, although depth localization is not pos-sible.

Deceleration time: The time duration (in mil-liseconds) of the decrease from peak flow velocity tothe zero baseline.

Diameter: The maximal linear measurement (incentimeters) of a circle.

Diastolic filling period: The duration of flowvelocity from atrioventricular valve opening to clo-sure.

Doppler equation:A mathematical equation thatrelates the observed frequency shift (∆F) to thevelocity of blood cells (V), the carrier frequency (Fo),the cosine of the angle theta (θ), and the speed ofsound in soft tissue (c = 1540 m/s). The Dopplerequation is ∆F = (V × 2 Fo × cos θ)/ c.

Ejection time:The duration of flow from semilu-nar valve opening to closure.

Flow convergence region:The region proximalto a flow orifice in which flow streamlines converge,thereby creating “shells” of progressive flow acceler-ation. Isovelocity areas can be indicated by aliasingboundaries.

Flow profile: A spatial plot of velocity distribu-tion across a vessel diameter that can be described asparabolic, flat, or irregular.

Frequency shift: The difference between trans-mitted and received ultrasound frequency. It isdirectly proportional to the velocity of blood flow asstated in the Doppler equation.

Gradient: The pressure drop or pressure differ-ence across any restrictive orifice.

Hertz:A unit of frequency equal to one cycle persecond;kilohertz (KHz) = 1000 hertz, and megahertz= 1 million hertz.

High pulse repetition frequency (PRF) Dop-pler: A method of achieving high sampling rates;

multiple pulses and their return signals from with-in the heart are present at any one point in time,and Doppler shifts along the beam are summedalong sample volume depths that are multiples ofthe initial sample volume depth to give a single out-put.

Isovolumic contraction:The time period (in mil-liseconds) between atrioventricular valve closureand semilunar valve opening.

Jet: High-velocity flow signal in or downstreamfrom a restrictive orifice.

Laminar flow:A flow state in which blood cellsare moving in a uniform direction and with orga-nized distribution of velocities across the f lowarea.

Mean velocity:The mean (average) of measuredspectral shifts over a specific period within a givensample site.

Mirroring:An artifact of spectral display resultingin the inability of the spectrum analyzer to separateforward and reverse Doppler signals. The strongersignals are displayed in mirror-like fashion from thezero baseline in the opposite channel.Also called sig-nal “cross talk.”

Modal velocity:The mode in the frequency analy-sis of a signal is the frequency component that con-tains the most energy. In display of the Doppler fre-quency spectrum, the mode corresponds to thebrightest (or darkest) display points of the individualspectra and represents the velocity component thatis most commonly encountered among the variousmoving reflectors.

Nyquist limit:The highest Doppler shift frequen-cy that can be measured. Equal to one half the pulserepetition frequency.

Pressure half time: The time (in milliseconds)that it takes for the maximal pressure gradient todecrease by one half.

Pulse repetition frequency (PRF):The rate atwhich pulses of ultrasound energy are transmit-ted.

Pulsed-wave (PW) Doppler: A method ofDoppler interrogation that uses specific time delaysto assess the Doppler shifts within a discrete regionalong the path of the sound beam.

Sample volume: The specific 3-dimensional sitein which Doppler velocities are interrogated.

Sample volume width:The lateral and azimuthaldimensions of the PW Doppler sample volume,which depends on beam characteristics.

Sample volume length:The axial size of the PWDoppler sample volume.

Spectral analysis:A display of the Doppler shiftfrequency components over time. Frequency or

velocity is displayed in the Y-axis, time in the X-axis,and amplitude in gray scale.

Spectral broadening:An increase in the numberof frequency components in a PW Doppler signal; anindicator of a disorganized flow pattern or high-velocity flow signal aliasing.

Velocity-time integral (VTI): Integral of thevelocity over time.


Turbulent flow: Nonlaminar unstable blood flowin which the kinetic energy of flow creates vorticesof differing velocities and direction.

Vena contracta: Smallest area of flow in or down-stream from a restrictive orifice.

Wall filter: A control that rejects echocardio-graphic information from low-velocity reflectorssuch as wall motion.

Recommendations for Quantification of Doppler ...color flow Doppler can help determine the direction...

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