DIAGNOSTIC METHODSDOPPLER ECHOCARDIOGRAPHY

Noninvasive estimation of right ventricular systolicpressure by Doppler ultrasound in patients withtricuspid regurgitationPAUL G. YOCK, M.D., AND RICHARD L. Popp, M.D.

ABSTRACT We evaluated the accuracy of a noninvasive method for estimating right ventricularsystolic pressures in patients with tricuspid regurgitation detected by Doppler ultrasound. Of 62patients with clinical signs of elevated right-sided pressures, 54 (87%) had jets of tricuspid regurgita-tion clearly recorded by continuous-wave Doppler ultrasound. By use of the maximum velocity (V) ofthe regurgitant jet, the systolic pressure gradient (AP) between right ventricle and right atrium was

calculated by the modified Bernoulli equation (AP = 4V2). Adding the transtricuspid gradient to themean right atrial pressure (estimated clinically from the jugular veins) gave predictions of rightventricular systolic pressure that correlated well with catheterization values (r = .93, SEE = 8 mmHg). The tricuspid gradient method provides an accurate and widely applicable method for noninvasiveestimation of elevated right ventricular systolic pressures.

Circulation 70, No. 4, 657-662, 1984.

A NUMBER of noninvasive methods for assessingright ventricular pressure have been developed basedon physical examination results and the use of electro-cardiograms, phonocardiograms, chest x-rays, andechocardiograms. ' '° While these methods can dis-criminate mild from severe right ventricular pressureelevation, they lack sufficient sensitivity to be useful inevaluating the effects of short-term therapeutic inter-ventions or in monitoring the clinical course of outpa-tients.

Recently, Skjaerpe and Hatle" demonstrated thatthe gradient across a regurgitant tricuspid valve can beestimated from the peak velocity of the systolic trans-tricuspid jet recorded by Doppler ultrasound. Theyconcluded that prediction of right ventricular systolicpressure should be possible in patients with tricuspidregurgitation by adding the Doppler-determined trans-tricuspid gradient to the right atrial pressure estimatedclinically. Experience in our laboratory and at otherinstitutions has indicated that tricuspid regurgitationsignals are detected by the Doppler method in a highproportion of patients with elevated right ventricularsystolic pressures, even when clinical signs of tricus-

From the Cardiology Division, Stanford University School of Medi-cine, Stanford.

This work was supported in part by grant no. T 32 HL 07625 from theNational'Institutes of Health, Bethesda.

Address for correspondence: Richard L. Popp, M.D., Stanford Uni-versity Medical Center, Stanford, CA 94305.

Received Jan. 31, 1984; revision accepted May 31, 1984.

Vol. 70, No. 4, October 1984

pid regurgitation are not explicit.", 12 Thus, a methodfor estimating right ventricular pressures based onDoppler-detected tricuspid regurgitation might havewide applicability.The purpose of this study was to test the accuracy of

the tricuspid gradient method in prospectively estimat-ing right ventricular systolic pressures in a group ofpatients with Doppler-detected tricuspid regurgitationwho underwent catheterization within 24 hr of theirDoppler study.

Material and methodsThe study group consisted of 62 patients in whom elevation

of right-sided pressures was suspected on the basis of results ofphysical examination (loud pulmonic closure sound, rightventricular lift), chest x-ray (right ventricular enlargement,prominent pulmonary vasculature), and/or two-dimensionalechocardiography (right ventricular chamber enlargement,"'D"-shaped left ventricle'0). Fifteen of the 62 patients werediagnosed as having clinical tricuspid regurgitation on the basisof results of physical examination by the primary ward physi-cian. Criteria used for the clinical diagnosis of tricuspid regurgi-tation included systolic murmur with positive Carvallo's sign,prominent jugular venous "c-v" and hepatic pulsations, andright-sided S3. Specific criteria applied in a given case were notalways stated in the medical record so we did not collate theincidence of such signs. The group included 35 male and 27female patients with ages ranging from 16 to 90 (mean 50)years. Primary cardiac diagnoses were cardiomyopathy (29 pa-tients), rheumatic valvular disease (15), myocardial infarction(five), nonrheumatic mitral regurgitation (three), cor pulmonale(two), aortic stenosis (one), primary pulmonary hypertension(one), congenital tricuspid regurgitation (one), anomalous pul-monary venous return (one), left atrial myxoma (one), myocar-

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ditis (one), carcinoid (one), and pulmonic stenosis (one). Pre-dominant rhythm at the time of study was sinus in 32, atrialfibrillation in 18, sinus tachycardia in eight, paced in three, andectopic atrial tachycardia in one.

Doppler studies were performed with a combined two-dimen-sional and Doppler ultrasonograph with a 2.5 MHz transducer.*Doppler recordings were made in the continuous-wave mode toallow unambiguous measurement of high velocities. Locationof the regurgitant jet was verified with the pulsed Dopplermode, which detects flow in a movable small-volume elementdisplayed on the two-dimensional echocardiographic image.A continuous-wave Doppler signal was accepted as repre-

senting tricuspid regurgitation if (1) the signal was recordedonly when the Doppler cursor was within the boundaries of theright heart (specifically not encroaching on the region of aorticoutflow), (2) the pulsed wave examination confirmed the pres-ence of a regurgitant jet originating from the tricuspid valve anddirected back into the right atrium, (3) the signal extended for atleast half of systole, and (4) a characteristic high-pitched signalwas produced by the audio output of the instrument. Validationof these criteria has been published elsewhere.' In somecases adequate recording of the regurgitant jet was obtainedonly with the smaller nonimaging Doppler transducer (whichhas the advantages of both increased maneuverability and high-er signal-to-noise ratio). In these cases, identification of thesignal as tricuspid regurgitation was supported by placing thenonimaging transducer in the same orientation as for the tricus-pid valve recording with the two-dimensional/Doppler imagingtransducer and by seeing tricuspid inflow in the same pattern asrecorded with the combined probe.

In a given patient the tricuspid regurgitation jet was soughtfrom all available midprecordial and apical positions until aflow signal with the maximum spectral representation of highvelocities was recorded. As Hatle`6 has emphasized, once asignal with a relatively dense high-velocity spectral representa-tion is obtained, the angle between the ultrasound beam and thedirection of flow can be assumed to be minimal. Confirmationof a narrow beam-to-flow angle was provided by the two-di-mensional image showing the Doppler cursor close to the pre-sumed direction of flow. No attempt at correction of velocitiesfor flow angle was made in any case. In our patient groupoptimal transducer locations were approximately equally divid-ed between the apical four-chamber view and a nidprecordialview, with medial angulation to insonify the tricuspid valve.

The mean jugular venous pressure was measured in centi-meters above the sternal angle at 45 degrees elevation of thethorax and head (higher or lower angles were required in somepatients when the venous pulsations were not clear). Right atrialpressure was estimated by adding 5 cm to the jugular venouspressure measurement. 17 Conversion to millimeters of mercurywas accomplished by dividing the right atrial pressure in centi-meters by 1.3, which expresses the relative density of mercuryto blood at physiologic temiperatures.

The maximum velocity of regurgitant flow for a given patientwas taken as the average peak velocity among those beats thatproduced the most complete envelopes and had the greatestrepresentation of high velocity flows in the spectral display. Foreach beat analyzed, peak velocity was assigned to the highestcoherent boundary on the spectral wave form (figure 1). At least4 beats were averaged for patients in sinus rhythm, at least 8beats for those in atrial fibrillation. Consecutive beats wereanalyzed only when the signal quality of all consecutive beatswas optimal (less than half of the patients in our group). Thetranstricuspid gradient (AP, in mm Hg) was approximated, withthe modification of the Bernoulli equation developed and vali-dated by Holen, Hatlc, and their colleagues,21-25 as follows: AP

= 4V2, where V represents the average maximum velocity inmeters per second (figure 1). For each patient the calculatedgradient was added to the estimated right atrial pressure (figure2) and the resulting prospective, blinded, right ventricular pres-sure predictions were compared with catheterization data bylinear regression analysis.The records of 25 alternately numbered patients in the series

were remeasured by the original observer at another sitting and

A.

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1TF

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FIGURE 1. Representative Doppler tricuspid regurgitation (TR) sig-nals from a patient in sinus rhythni (A) and atrial fibrillation (B). The

l)opplcr cursor is shown on the two-dimensional image crossing theregion of the tricuspid valve (TV) orifice, parallel to the presumeddirection of the jet. By convention, tlow toward the transducer is dis-

played above the baseline (tricuspid inflow, TF). Maximum velocitiesin meters per second are indicated for each beat along with the calibra-tion scale. Long arrows designate the approximate onset of nechanical

systole, assigned at a point msec beyond the apparent initial QRSdeflection on the clectrocardiogram. RV = right ventricle.

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*lrex System IIIB and Exemplar: Ramsey, NJ.

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DIAGNOSTIC METHODS-DOPPLER ECHOCARDIOGRAPHY

JVP

\ /~RVSP\

JVP +AP =RVSPFIGURE 2. Schema for the method of estimating right ventricularsystolic pressure (RVSP) from mean jugular venous pressure (JVP) andmaximum transtricuspid gradient (AP). The mean JVP is approximatedas the height above the sternal angle plus 5 cm. This figure is divided by1.3 to convert centimeters of blood to millimeters of mercury. Thetranstricuspid gradient (AP, in mm Hg) is calculated by use of themodified Bernoulli equation, AP = 4V2, where V represents the maxi-mum velocity of the regurgitant jet in meters per second. Right ventricu-lar systolic pressure is then estimated as the sum of the mean JVP andthe transtricuspid gradient.

again by a second observer. In both cases observers were blind-ed to the primary results. All patients underwent catheterizationwithin 24 hr of their Doppler study. Fourteen patients had in-dwelling pulmonary arterial (Swan-Ganz) catheters at the timethe Doppler examination was performed. In these patients pul-monary arterial systolic pressures were recorded as a close ap-proximation of the right ventricular systolic pressures. All 14patients in this latter group had right ventricular pressures thatdiffered less than 4 mm from the pulmonary arterial pressure atthe time of catheter insertion. The remainder of the patients inour series had right heart pressures measured only in the cath-eterization laboratory by standard fluid-filled catheters andrecording equipment described elsewhere.'8 Pressure determi-nations from catheterization alone and measurements of theSwan-Ganz pressure tracings were made without knowledge ofthe Doppler findings.

ResultsOf the 62 patients recruited for the study on the basis

of clinically suspected elevation of right-sided pres-sures, 56 had Doppler-detected tricuspid regurgitation(90%). Only 15 patients in this group had tricuspidregurgitation by conventional clinical criteria (25%).Full spectral profiles of the regurgitant flow signalswere obtained in 54 of 56 patients (96%); in the re-

maining two poor signal-to-noise ratios with high-ve-locity dropout precluded determination of the maxi-mum velocity of the regurgitant jet.

Comparison of Doppler-estimated and catheteriza-tion-measured right ventricular systolic pressures isshown in figure 3. The standard error of the estimate is8 mm Hg and the slope and intercept of the linearregression function are not statistically different from1.0 and zero, respectively. The correlation coefficientis high (r = .93), in part because of one extreme datapoint from the patient with pulmonary stenosis. If thedata from this patient is excluded from analysis, the rvalue decreases to .89.

DiscussionThe results of this study confirm the previous sug-

gestion that right ventricular systolic pressures can bepredicted in patients with Doppler-detected tricuspidregurgitation by adding the calculated transtricuspidgradient to the estimated right atrial pressure. Thesedata extend the work of Skjaerpe and Hatle,' whoshowed that in patients with tricuspid regurgitation thesystolic transtricuspid gradient (AP) can be estimatedby a modification of the Bernoulli equation, AP =4V2, where V represents the maximum velocity re-corded in the regurgitant jet. Our study demonstratesthe practical application of the tricuspid gradient meth-od in an adult population with various forms of cardio-pulmonary disease.

Sources of error. A potentially major source of error indata acquisition in the majority of patients is the use of

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140

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CATHETERIZATION RV SYSTOLIC PRESSURE (mm Hg)

FIGURE 3. Correlation of Doppler-predicted and catheterization-mea-sured right ventricular systolic pressures (n = 54). Simultaneous Swan-Ganz pressure measurements are indicated as open circles and pressuresfrom the nonsimultaneous catheterization studies as closed circles. Theregression function is plotted as a solid line that is nearly superimposedon the identity function (dashed line). RV = right ventricle.

7

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nonsimultaneous catheterization data for correlationwith Doppler-predicted pressures. No patient in thisstudy group had significant changes in therapy or clini-cal status between the time of the Doppler study andcatheterization, and all received oral hydration andonly light sedation (5 to 10 mg oral diazepam) beforecatheterization. Nonetheless, drift in right-sided pres-sures undoubtedly occurred in some patients. Whenthe patients studied with the use of simultaneous pul-monary pressure measurements are analyzed as a sub-group, correlation is in fact closer than for the entiregroup (r = .97 vs .93). However, the power of thissubgroup analysis is limited by the small number ofpatients undergoing simultaneous pressure measure-ment and by the use of pulmonary arterial pressuresrather than direct right ventricular pressure measure-ments in these patients.A possible methodologic error arises because the

precise atrial pressure at the time of peak transtricuspidflow is not clinically measurable. Jugular venous pres-sure in this study was taken as an estimated mean of thepulsations in the jugular vein, i.e., generally as lessthan the v wave. There is theoretical support for the useof a mean pressure estimate rather than the v wave inright ventricular pressure calculations. As shown infigure 4, the maximum systolic gradient between rightventricle and right atrium occurs in midsystole beforethe peak of the v wave. Use of a prominent v wave inthe jugular venous pressure for the calculation mightlead to overestimation of right ventricular systolicpressures.

The clinical estimation of right atrial pressure fromthe jugular venous pulse is a significant and unavoid-

v v

I ~~~~~~~RAMILD TR SEVERE TR

FIGURE 4. Demonstration of the maximum gradient (APmax) betweenright ventricular (RV) and right atrial (RA) pressures. APmax, corre-sponding to the highest velocity of transtricuspid regurgitant flow, oc-curs before the peak v wave in the right atrial pressure. Adding the vwave pressure to the peak transtricuspid gradient would overestimatethe right ventricular systolic pressure.

660

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CATHETERIZATION MEAN RA PRESSURE (mm Hg)

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140

120

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CATHETERIZATION GRADIENT (mm Hg)

FIGURE 5. Clinical estimates of mean jugular venous pressure (top)and Doppler-estimated transtricuspid gradients (bottom) compared withcatheterization values in 53 patients. One patient was excluded becauseright atrial pressure measurements were not recorded in the catheteriza-tion laboratory. Dashed line is the line of identity. 0 = simultaneousSwan-Ganz pressure measurements, nonsimultaneous measure-

ments in the catheterization laboratory: JVP = jugular venous pressure;

RA = right atrial pressure.

able source of error. Figure 5 shows the poor correla-tion between clinically estimated and catheterization-measured values for right atrial pressure, and therelatively good correlation of Doppler-estimated andcatheterization-measured transtricuspid gradients.Fortunately, the estimates of right atrial pressure are

generally smaller than the gradient determinations(mean 11.8 vs 38.6 mm Hg). It follows that the abso-lute deviations from the true right atrial pressures are

correspondingly small values, so that their effect on

relative error in right ventricular pressure estimationsis partially diluted (compare figure 5 and figure 3).The Doppler-determined gradients are also subject

to a number of potential errors. The assumption thatthe beam-to-flow angle is negligible cannot be directlyvalidated. In the present study we found that in all

CIRCULATION

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DIAGNOSTIC METHODS-DOPPLER ECHOCARDlOGRAPHY

cases the Doppler cursor could be placed in a positionthat appeared parallel to the presumed direction offlowin the plane of the echocardiographic display. Evenallowing an angle deviation of 10 degrees in the un-

known azimuthal or z axis, the error is minimal. TheDoppler equation states that the measured velocity isunderestimated by the factor Cos(O), where 0 is theangle discrepancy between beam and flow. Thus, for a

10 degree angle, velocity is underestimated by only1.5%. This percent error is approximately doubled inthe gradient calculation, however, since the velocityterm is squared. *

At least as important a source of error is the assign-ment of the maximum velocity of the regurgitant sig-nal. In a given patient relatively few beats may have an

optimal spectral profile. Changes in signal-to-noiseratio on a beat-to-beat basis are caused by patient/transducer motion, differing cardiac cycle lengths, andrespiratory variation. The possibility of a systematicerror in estimation of mean gradient occurs in the lattertwo categories if good quality signals are recorded onlyat certain cycle lengths (e.g., with longer R-R inter-vals) or at certain phases of respiration (e.g., onlyduring inspiration).

Even with an ideal spectral contour, assigning themaximum velocity is arbitrary to some extent. Themaximum velocity contour is defined by visual inspec-tion of the spectral display and thus is subject to ob-server variability. To test the extent of interobservervariability, tracings from 25 consecutive even-num-

bered cases were analyzed by a second investigatorwho was blinded to the results obtained by the firstobserver. The interobserver variability in calculatedgradients was low, with a mean discrepancy of - 1.8mm Hg and an SD of 4.9 mm Hg. The same tracingswere reanalyzed by the initial observer in a blindedfashion, yielding an intraobserver mean discrepancy of-0.2 mm Hg and an SD of 3.4 mm Hg.

In addition to observer variability in measurement,there is intrinsic uncertainty in the actual spectral sig-nal introduced by the "transit time" effect, a limitationin the accuracy of Doppler velocity determinationsimposed by short sampling periods.20 The gradient cal-culation itself is an approximation based on simplify-ing assumptions about the characteristics of flowthrough the valve.2'-23 These assumptions have beenvalidated in vitro2' and are supported by a number ofclinical series on stenotic valves.'6 21-27 In practice,these technical errors in measuring velocity and calcu-lating the gradients are probably small relative to the

biologic variables (difficulty in assessing right atrialpressure, angle of flow, and variability in signal-to-noise) discussed above.

Utility of the method. Our preliminary findings sug-

gest that Doppler-detected tricuspid regurgitation ispresent in a high proportion of patients with elevatedright-sided pressures (in significantly more patientsthan in whom tricuspid regurgitation is recognizedclinically). Other investigators also have reported a

high incidence of Doppler-detected tricuspid regurgi-tation in this group. l 12 The fact that tricuspid regurgi-tation is subclinical in most cases does not preclude use

of the gradient method to estimate right ventricularsystolic pressures: the calculations depend on the ve-

locity, and not the volume, of flow. All that is requiredfor use of the tricuspid regurgitation signal is a fullspectral profile which, in our experience, is found innearly all patients (96%) with Doppler-detected tricus-pid regurgitation. We did not explore the use of con-

trast echocardiographic enhancement in this study,which might have provided an even higher yield ofinterpretable tricuspid regurgitation signals?25

Whether or not the method is sensitive enough tofollow the effects of therapeutic interventions on right-sided pressures remains to be proved. Theoretically,some of the variables that lead to inaccuracy (in par-

ticular the beam angle and ambiguity in assigning themaximum velocity) may be constant errors in a givenpatient and thus may be less important in followingchanges in pressure than in predicting absolute pres-

sures.

Finally, in this series we did not compare the tricus-pid gradient method with any of the recently publishedDoppler techniques for estimating pulmonary arterialpressures based on the pulmonic flow velocity con-

tours29 30 and timing of right-sided valve events.3' In a

given patient either the tricuspid gradient method or

the pulmonic flow techniques may be preferable, de-pending on the quality and accessibility of the corre-

sponding Doppler signals.

We thank Kitty Kisslo and Corrie Naasz for their skilledassistance with the Doppler studies, and Gretchen Houd for hercareful manuscript preparation.

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*As shown by Taylor expansion of the velocity-plus-error term.`9

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P G Yock and R L Popppatients with tricuspid regurgitation.

Noninvasive estimation of right ventricular systolic pressure by Doppler ultrasound in

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1984 American Heart Association, Inc. All rights reserved.

is published by the American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231Circulation doi: 10.1161/01.CIR.70.4.657

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