Determination of Aortic Valve Area by Two-Dimensional and Doppoler Echocardiography in Patients With Normal and Stenotic Valves

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1 jacc Vol. 15, No. 4 Mrch : METHODS Determintion of Aortic Vlve Are by Two-Dimensionl nd Doppoler Echocrdiogrphy in Ptients With Norml nd Stenotic Vlves ROBERT M. ROTHBART, MD, FACC, JORGE L. CASTRO MD,* LINDA V. HARDING, RDMS, CHARLES D. RUSSO, MD, STEVEN M. TFAGUE, MD, FACC* Mimi, Florid nd Oklhom City, Oklhom To ssess the fesibility nd ccurcy of determining bioprosthetic ortic vlve re from two-dimensionl nd Doppler echocrdiogrphic mesurements, three prtilly overlpping groups were selected from 55 ptients with such bioprosthetic vlves nd dequte Doppler studies. These were Group 1, 37 ptients with recent ortic vlve replcement surgery nd no clinicl or ech6crdlogrphic evidence of vlve dysfunction ; Group 2, 12 ptients with prosthetic vlve stenosis documented by crdic ctheteriztion ; nd Group 3, 22 ptients with both Doppler nd ctheteriztion studies in whom noninvsive nd invsive determintions of ortic vlve re could be directly compred. Left ventriculr outflow trct dimeter ws mesured from two-dimensionl still frme imges. Flow velocity proximl to the ortic vlve, trnsvlvulr velocity nd ccelertion time were determined from pulsed nd continuous wve Doppler spectr. Aortic vlve grdient ws clculted with the modified Bernoulli eqution nd vlve re by the continuity eqution. In the 37 ptients with norml) functioning vlve, the clculted men grdient rnged from 5 to 25 mm Hg (verge 13.6 :k 5.2) nd vlve re from 1. to 2.3 cm 2 (men 1.6 :t.31). Liner regression nlysis of prosthetic ortic vlve re determined by Doppler imging nd crdic ctheteriztion demonstrted high correltion (r =.93) between the two techniques. Comprison of the ptients with nd without prosthetic vlve stenosis reveled sttisticlly significnt differences in men grdient (42.8 ± 12.3 versus 13.6 ± 5.2 mm Hg ; p =.1), ccelertion time (116 ± 15 versus 8 ± 13 ms ; p.1) nd vlve re by the continuity eqution (.8.16 versus cm 2 ; p =.1). Individul ultrsound vribles were ssessed for their utility in recognizing bioprosthetic vlve stenosis. When dignostic criteri were selected to mintin bsolute specificity, either n bnormlly high men grdient or noniny vsively determined vlve re < I cm 2 identified 92% of ptients with stenotic vlve. Mrginlly lower sensitivity ws ssocited with n elevted pek grdient or prolonged ccelertion time ; ech identified 75% of the ptients with vlve stenosis. However, mesurement of the rtio of left ventriculr outflow trct to trnsvlvulr velocity time integrls further improved dignostic ccurcy. All 37 ptients with norml prosthetic vlve hd rtio >.35, wheres ech of the 12 ptients with vlve stenosis hd lower rtio. In conclusion, ssessment of prosthetic ortic vlve re by crdic ultrsound is highly ccurte nd cn be useful in the dignosis of bioprosthetic ortic vlve stenosis. (J Am Coil Crdiol 199 ; ) The ccurcy of two-dimensionl nd Doppler echocrdiogrphy for determining trnsvlvulr grdient (1-3) nd ortic vlve re (4-6) in dult ptients with ortic stenosis hs From the Division of Crdiology, Deprtment of Medicine, University of Mimi School of Medicine, nd Veterns Affirs Medicl Center, Mimi. Florid ; nd Deprtment of Medicine, Division of Crdiology. University of Oklhom School of Medicine, Oklhom City, Oklhom. Mnuscript received June 2, 1989 ; revised mnuscript received October 25, 1989, ccepted November I Address for reprints : Robert M. Rothbrt, MD, University of Colordo School of Medicine, Division of Crdiology (B-13),42 Est Ninth Avenue. Denver, Colordo by the Americn College of Crdiology been well estblished. Considerbly less informtion is vilble regrding the role of crdic ultrsound in ssessing prosthetic ortic vlves. Doppler grdient estimtes cross bioprosthetic nd Bj6rk-Shiley vlves (7-9) implnted in the ortic position hve correlted well with mesurements mde t crdic ctheteriztion ; however, this hs not been the cse for Strr-Edwrds vlves (1). In only one preliminry study (11) hve noninvsive prosthetic vlve re determintions been reported ; these were obtined from ptients with normlly functioning Bjork-Shiley vlve nd were not verified by comprison with ctheteriztion dt /91$*1.5

2 818 ROTHBART ET AL. JACC Vol. 15, No. 4 Mrch 15,19%: Becuse stenosis of mechnicl vlves occurs infrequently, noninvsive techniques for identifying prosthetic vlve stenosis re of greter clinicl vlue in ptients with bioprosthetic device. Unfortuntely, stndrd echocrdiogrphic imging employing M-mode nd two-dimensionl techniques often fils to dequtely delinete the vlve leflets in these ptients. As result, it my be difficult or impossible to identify signs of vlve dysfunction, including thickening, clcifiction or restricted leflet motion. In these cses, noninvsive techniques to estimte ortic vlve re could be extremely vluble. Thus, the present study ws undertken to ssess the ccurcy of two-dimensionl nd Doppler echocrdiogrphy in estimting bioprosthetic ortic vlve re nd to determine the vlue of this technique in the dignosis of bioprosthetic vlve stenosis. Methods Study ptients. The study group comprised 56 ptients ged 37 to 81 yers ; 8 were women nd 48 were men. The gols nd methods of this investigtion were explined to ech subject nd written informed consent ws obtined ccording to the protocol pproved by our institutionl review bords. Thirty-eight ptients hd undergone ortic vlve replcement I to 24 months before entering the study ; they denied ll crdiovsculr symptoms, hd norml usculttory findings, other thn grde 2-3/6 systolic ejection murmur, nd hd norml findings on crdic ultrsound studies. Specificlly, ortic vlve leflets, if imged, mesured <3 mm in thickness nd demonstrted norml excursion without prolpse. No discordnt motion of the sewing ring ws visulized. Aortic regurgittion ws judged by Doppler study to be either bsent (n = 21) or mild (n = 17) with regurgitnt flow detectble <_ 1.5 cm proximl to the ortic vlve. These ptients were considered to hve norml prosthetic vlve function. A 24 month limit between vlve replcement surgery nd study entry ws selected for this norml group, becuse bioprosthetic vlve clcifiction or dysfunction is extremely unlikely within the first 2 yers fter implnttion in uults (12,13). Twelve dditionl ptients hd bioprosthetic ortic stenosis (vlve re <1. cm 2) verified by crdic ctheterizlion. The remining six ptients hd undergone ortic vlve replcement surgery >24 months before Doppler studies (rnge 51 to 127 months), but crdic ctheteriztion performed within 2 months of the Doppler exmintion verified norml vlve function. These 6 ptients, together with ll 112 ptients with stenosis nd 4 norml ptients who hd undergone postopertive ctheteriztion formed cohort of 22 ptients whose noninvsive nd invsive mesurements of ortic vlve re could be directly compred. Two-dimensionl nd Doppler echocrdiogrphy. Echocrdiogrphic exmintions were performed with l ewlett Pckrd 772AC crdic ultrsound system. The videotped studies were reviewed nd Doppler spectr mesured on n off-line video nlysis system (MicroSonics CAD886), which digitlly smples such dt t 1 ms intervls. Aortic vlve re (A VA) ws clculted with use of the continuity eqution (4-6): AVA = -rr(di2) 2 (VLVOTNAV), where D = the dimeter of the left ventriculr outflow trct, VLVOT = the velocity time integrl of flow from the left ventriculr outflow trct nd V AV = the velocity time integrl of flow through the ortic vlve. The dimeter of the left ventriculr outflow trct ws mesured s the perpendiculr distnce between the inner edges of its nterior nd posterior spects just proximl to the sewing ring of the ortic vlve in left prsternl long-xis still frme imges. Multiple mesurements were performed in conjunction with slight chnges in trnsducer ngultion until reproducible mximl vlue ws obtined. Pulsed Doppler mesurements offlow velocity in the left ventriculr outflow trct were recorded by plcing the smple volume in the body of the left ventricle, dvncing grdully towrd the ortic vlve until mrked increse in Doppler pek velocity ws detected nd then withdrwing slightly. The site identified by this method ws typiclly.5 to 1 cm proximl to the ortic vlve leflets. If vlve leflet clicks were noted in the spectrl trcing, the smple volume ws considered to be iruploperly positioned nd ws moved to slightly more proximl loction. The highest velocity signls meeting the preceding criteri were selected for nlysis ; mesurements from three successive curves were verged. Filtering ws mintined t miniml level to fcilitte ccurte identifiction of flow onset nd termintion. Continuous wve Doppler spectr of trnsvlvulr flow were recorded from the picl, right prsternl nd suprsternl trnsducer positions in ll ptients. Trnsducer position nd ngultion were mnipulted until mximl velocities nd the purest uditory signls were obtined. As ws the cse for pulsed Doppler ultrsound, the miniml low pss filter setting consistent with dequte definition of the spectrl envelope ws employed. Pek nd men velocities, s well s time to pek velocity, were mesured utomticlly by our computer nlysis system from the digitized Doppler spectr. Accelertion time ws defined s the intervl between initil nd mximl flow velocity. Men grdient ws clculted by pplying the modified Bernoulli eqution (1) to velocity mesurements obtined t 1 ms intervls throughout systole. Doppler signls from one ptient with recently implnted nd cliniclly norml vlve were unmesurble becuse of poor qulity nd were excluded from further dt nlysis. Thus, techniclly dequte exmintions were

3 JACC Vol. 15, No. 4 Mrch 15,199: ROTHEART ET AL. B11PROSTHETIC AORTIC VALVE AREA 819 vilble in 55 (98%) of our.56 ptients in the initil study group. Crdic ctheteriztion. After sedtion with 5 mg of orl dizepm, crdic ctheteriztion ws performed in 4 of the ptients with recently implnted norml vlve, in 12 ptients with prosthetic vlve stenosis nd in 6 dditionl ptients who hd ortic vlve replcement >24 months before ctheteriztion nd hd no stenosis. A men intervl of 22 dys (rnge I to 161) seprted the echocrdiogrphic study from ctheteriztion. The clinicl sttus of ll ptients remined stble during this intervl. Pressure mesurements in the left ventricle were obtined by wy of 7F or 8F fluid-filled ctheter pssed retrogrde cross the ortic vlve. Trcings from the proximl ort were recorded fter pullbck. Aortic regurgittion ws identified by ortic root ngiogrphy in the right nterior oblique projection employing 4 to 6 ml of contrst gent injected t rte of 2 to 25 ml/s. Severity of regurgittion ws grded on scle from to 4+ (14). Thermodilution crdic output ws employed for ortic vlve re clcultions by the Gorlin eqution except in four ptients with moderte or severe ortic regurgittion, in whom ngiogrphic determintion of crdic output ws used. Grdients were clculted by verging mesurements from three successive crdic cycles. Sttisticl nlysis. Commercilly vilble softwre (SAS, SAS Institute) ws employed for dt storge nd nlysis. The significnce of differences between mens ws determined by pired or unpired Student's t tests s pproprite ; verge vlues re reported s men vlues ± I SD ; correltion ws ssessed by liner regression nlysis ; nd Person r vlues were compred by the test for differences between dependent correltions. Results Comprison of noninvsive (Doppler) nd invsive ortic vlve re mesurements (Fig. 1). There ws close nd highly significnt correltion between ssessments mde by crdic ultrsound nd ctheteriztion (r =.93 ; p =.1). Exmintion of the regression line, which hs slope close to 1 nd intercept pproximting, indictes tht prosthetic ortic vlve re mesurements by the two techniques re comprble. However, there ws slight but significnt tendency for the ctheteriztion-derived vlve res to exceed the Doppler-derived vlues (in 68% of ptients ; p =.5). Averge ctheteriztion vlve re ws greter thn tht clculted by Doppler ultrsound (1.17 ±.47 versus 1.9 ±.38 CM2), difference tht is mrginlly significnt (p =.56). Norml vlves. Mesurements of men trnsvlvulr grdient, ccelertion time nd vlve re from the 37 ptients with normlly functioning bioprosthetic ortic vlve re presented in Figure 2 grouped ccording to externl vlve T =.93 (N=221 Cth =1.16 Dopp-.()g 1 2 DOPPLER VALVE AREA (= 2 ) Figure 1. Scttergrm of ortic vlve re determined by Doppler (Dope) versus vlve re mesurement by the Gorlin eqution (Cth) for the 22 ptients with crdic ctheteriztion dt. The regression eqution for the solid regression line is given. The dsh line of identity is lso included. dimeter. Men grdient rnged from 5 to 25 mm Hg (verge 13.6 ± 5.2) nd ccelertion time from 55 to 15 ms (men 8. ± 13.). Aortic vlve re, clculted noninvsively by pplying the continuity eqution, rnged from 1. to 2.3 cm 2 (men 1.6 ±.31). Although individul Doppler vlve re clcultions vried considerbly mong ptients with identiclly sized vlves nd there ws substntil overlp between groups with different vlve sizes, there ws significnt correltion between Dopp :er vlve re determintions nd externl vlve dimeters (r =.35 ; p =.3). A significnt inverse reltion existed between men trnsvlvulr grdient nd vlve size (r =.43 ; p =.8) ; miniml correltion ws found between ccelertion time nd vlve size (r =.19 ; p NS). Stenotic vlves. The 12 ptients with prosthetic ortic vlve stenosis proved by crdic ctheteriztion hd n ortic root dimeter of 1.6 to 2.2 cm (men 1.9 ±.8) nd left ventriculr outflow trct velocity of.68 to 1.7 m/s (men 1.2 ±.29), vlues similr to those observed in ptients with norml vlve (1.6 to 2.2 cm [men 2. ±.61 nd 1. to 1.8 m/s [men 1.3 ±.21, respectively). However, pek nd men grdients of 7 ± 21 nd 43 ± 12 mm Hg, respectively, in the ptients with stenotic ortic vlve gretly exceeded.nesurements in ptients with norml vlve (26 ± 1 nd 14 ± 5 mm Hg, respectively ; p =.1 for both comprisons) (Fig. 3). Accelertion time ws significntly longer (116 ± 15 versus 8 ± 13 ms ; p =.1) nd Doppler ortic vlve re considerbly smller (.82 ±.2 versus 1.63 ±.28 cm 2 ; p =.1) in the ptients with prosthetic vlve stenosis. If the Doppler grdients, ccelertion times nd vlve

4 82 ROTHBART ET AL. BIOPROSTHETIC AO".TIC VALVE AREA JACC Vol. 15, No. 4 Mrch 15,199: z W 2 z x 29 cc 3 1 W F 9 6 o 8 e t 8 -- fi I I VALVE EXTERNAL DIAMETER Figure 2. Doppler men grdient, ccelertion time nd ortic vlve re for 37 normlly functioning prosthetic vlves of different sizes s mesured by vlve externl dimeter (mm). Group mens re indicted by n open dimond. res recorded in our 37 norml ptients re considered to represent the norml rnges for these vribles, then 75% of exmintions in the 12 ptients with bioprosthetic vlve stenosis would hve yielded n bnorml ccelertion time or n elevted pek grdient, nd n incresed men grdient or decresed vlve re would hve been recorded in 92%. For every ptient with stenosis, t lest two of these four vribles were bnorml. I An lterntive strtegy wou?.j be to select criteri so s to minimize the totl number of errors in ssigning ptients to the norml group or the group with stenosis. Pursuing this course leds to identifiction of norml pek grdient s <48 mm Hg, norml men grdient s <26 mm Hg, norml ccelertion time s 51 ms nd norml Doppler vlve re s >1.1 cm2. Tble 1 presents the sensitivity, specificity nd totl predictive ccurcy for bnormlities of individul Doppler mesurements in identifying ptients with prosthetic ortic vlve stenosis. Although both ccelertion time nd pek grdient provide excellent seprtion of ptients with norml vlve from those with stenosis, men grdient nd Doppler vlve re re superior vribles, ech misclssifying only I of the 49 ptients. Effect of ortic regurgittion. Mild ortic regurgittion ws detected during the Doppler exmintion in 42% of our ptients with norml vlve. Erlier studies (6,15) indicted tht systolic flow velocity in the left ventriculr outflow trct my increse in ptients with substntil ortic regurgittion. Averge pek velocity mesured immeditely proximl to the ortic vlve in the 17 ptients with norml vlve nd ortic regurgittion (1.32 ±.22 m/s) did not differ significntly from the velocity obtined in those with norml vlve without regurgittion (1.38 ±.22 m/s), lending support to our judgment tht regurgittion ws mild. In 8 (36%) of the 22 ptients who underwent crdic ctheteriztion, ortic root ngiogrphy reveled ortic regurgittion?2+. In these ptients, verge left ventriculr outflow trct velocity exceeded the men vlue recorded in the 14 ptients with or I + regurgittion (1.41 ±.18 versus 1.2 ±.24 m1s ; p =,5). Contribution of left ventriculr outflow trct mesurement to vlve re determintion. Two-dimensionl imging generlly provided unmbiguous nd reproducible identifiction of the mximl inner dimeter of the left ventriculr outflow trct. Consequently, this mesurement ws used in the continuity eqution for the clcultion of vlve re. In some lbortories the left ventriculr outflow trct is not mesured ; rther, the externl dimeter of ech vlve s specified by the mnufcturer is employed to determine vlve re. For five of our ptients, whose vlve replcement surgery hd occurred mny yers erlier, records specifying the size of the device implnted could not be locted. In the Tble 1. Sensitivity, Specificity nd Totl Predictive Accurcy of Doppler Vribles in the Dignosis of Prosthetic Vlve Aortic Stenosis Prmeter Norml Vlue Sensitivity Specificity TPA Accelertion time <1 ms Pek grdient <48 mm Hg.75 Ion.96 Men grdient <26 mm Hg Doppler ortic vlve re >1.1 em TPA = totl predictive ccurcy.

5 JACC Vol. 15, No. 4 Mrch 15,199 : ROTHBART ET AL me Figure 3. Doppler pek nd men grdients, ortic vlve re nd ccelertion time for ptients with norml (n = 37) nd stenotic (n = 12) vlves. Group mens re indicted by n open dimond. The dshed horizontl lines denote the vrible vlues used in the nlysis of sensitivity nd specificity. remining 5 ptients, there ws wek but sttisticlly significnt correltion between our mesurement of left ventriculr outflow trct dimeter nd the mnufcturer's vlve size (r =.31 ; p =.25). This unimpressive correltion cn be explined if one considers the distribution of vlve sizes in our ptients, 43 (8) of whom hd 23, 25 or 27 mm devices. With n expected mesurement error of I to 2 mm (6), the bility to correctly ctegorize vlve size in these ptients is limited. When the prosthetic vlve dimeter is substituted for the left ventriculr outflow trct mesurement in the continuity eqution, there is respectble correltion between the noninvsively nd the invsively determined vlve re in the 22 ptients with ctheteriztion (r =.78 ; p =.1). However, this correltion is inferior to the result obtined when the ctul mesured outflow trct dimeter is used (r =.93 ; p =.1 for comprison of the two correltion coefficients). In fct, when we neglected subvlvulr re nd considered only the remining term from the continuity eqution, nmely, the rtio of the left ventriculr outflow trct velocity time integrl to trnsvlvulr velocity time integrl, the correltion with the ctheteriztion vlve re ws high (r =.87 ; p =.1). Thus, the outflow trct mesurement contributes little to the ccurcy of our noninvsive vlve re determintions bsed on the continuity eqution. In Figure 4 the reltion between the velocity time integrl rtio nd ctheteriztion vlve res is grphiclly presented. The distribution of rtios for ptients with nd without prosthetic vlve stenosis is lso shown. There is complete seprtion between these two groups ; ll ptients with stenosis hd rtio <.35, wheres lrger rtio ws recorded for ll those with norml vlve. Discussion Accurte determintions of trnsvlvulr ortic grdient nd vlve re hve been chieved by Doppler techniques (1-6). The fesibility of pplying these methods to ptients with bioprosthetic ortic vlve is much less certin. Verifiction of Doppler findings by pressure mesurements in substntil number of ptients with normlly functioning bioprosthesis hs not been reported. Sequentil or simultneous Doppler nd ctheteriztion dt re vilble for <2 ptients with bioprosthetic ortic stenosis (7-9) ; noninvsive ssessment of ortic vlve re ws not performed in ny of these cses. We restricted our study to bioprosthetic vlves for two resons. First, the centrl pttern of flow through these devices is similr to tht of stenotic ntive vlves for which the ccurcy of vlve re determintions from echocrdiogrphic nd Doppler mesurements hs been verified. See-

6 822 ROTHBART ET AL. JACC Vol. 15, No. 4 Mrch 15, 199 : A N r 7 I-. 5 Z w.5 1. y.4 N O.3 r W M -o VELOCITY TIME INTEGRAL RATIO NORMAL STENOTIC Figure 4. Anlysis of the reltionship between the velocity time integrl rtio (i.e., the rtio of the re under the left ventriculr outflow trct pulsed Doppler velocity curve to the re under the continuous wve Doppler trnsvlvulr flow spectrum) nd prosthetic ortic vlve re mesured t crdic ctheteriztion. In the left pnel, liner regression nlysis revels correltion coefficient of.87 for this comprison mong the 22 ptients with ctheteriztion dt. The regression line is shown. In the right pnel, velocity time integrl rtios re presented for the 37 ptients with cliniclly norml vlve nd the 12 with stenosis proved by ctheteriztion. The ptients with norml vlve hd rtio in excess of.35, wheres lower vlues were recorded in the 12 ptients with stenosis. ond, becuse the vst mjority of cses of prosthetic vlve stenosis occur in ptients with bioprosthesis, normtive dt for this type of vlve re cliniclly importnt. No ortic bioprosthetic vlves. Evlution of ortic vlve re by the continuity eqution requires mesurement of subortic dimeter from prsternl echocrdiogrphic imges, pulsed Doppler recordings obtined from the picl trnsducer position nd continuous wve Doppler evlution from the pex or right prsternl region. Although cquiring this informtion requires high degree of technicl skill, fesibility in the current study ws excellent, with dequte dt obtined from 98% of our study cohort of 56 ptients. The pek nd men grdients recorded by Doppler study in our group with norml bioprosthetic vlve were similr to vlues previously reported from both noninvsive (7-9) nd invsive (16,17) studies in ptients without pprent bioprosthetic ortic vlve dysfunction. Although reltively high grdient ws present in ptients with vlve of the smllest dimensions nd substntilly lower grdient ws recorded from ptients with vlve of the lrgest dimensions, there ws considerble overlp cross vlve size groups nd no difference t ll in vlve grdient between ptients with the two most commonly implnted sizes, 23 nd 25 mm. Nevertheless, moderte nd significnt inverse correltion between pek or men grdient nd externl vlve dimeter ws demonstrted. This is consistent with observtions from other lbortories (18). Becuse vlve grdient is relted to both effective vlve orifice nd trnsvlvulr flow, the mrked heterogeneity in mesured grdients my reflect, t lest in prt, differences in crdic output mong ptients. Our mesurements of Doppler ccelertion time for the norml bioprosthetic vlves re in the rnge of erlier reports for ntive ortic vlves without stenosis (19,2). There ws no significnt reltion between externl vlve dimeter nd ccelertion time in our norml group. The wide rnge of Doppler ortic vlve res (ll >-1 cm2) recorded in our ptients with norml vlve is similr to the vlues previously reported from ctheteriztion studies (16,17). Although substntil frction of the vribility in the clculted noninvsive vlve re is undoubtedly ccounted for by mesurement errors in velocity nd distnce determintions, portion is relted to ctul differences in vlve size, which ws significntly correlted with the Doppler-determined re. Moreover, studies (21,22) in which the re of norml prosthetic vlves ws mesured by the Gorlin eqution t rest nd during exercise hve suggested tht the effective orifice of these devices is not constnt. Increses in crdic output re ssocited with greter clculted vlve

7 JACC Vol. 15, No. 4 Mrch : ROTHBART ET AL. 823 re. Thus, differences in Doppler vlve re determintions mong ptients with single vlve size my be prtilly genuine, resulting from differences in trnsvlvulr flow. The clculted Doppler vlve res for the norml group nd the group with bioprosthetic stenosis overlpped only once. The ptient hd 23 mm Hncock vlve without clinicl evidence for dysfu,,-.tion tht hd been implnted 12 months before his echocruiogrphic nd Doppler study, t which vlve re of 1. cm2 ws determined. Mild ortic regurgittion ws present. Velocity mesurements in the left ventriculr outflow trct nd t the vlve level were within I SD of the group men vlue, however, the mesured dimeter of the outflow trct (1.6 cm) ws 2 SD below the men, the lowest vlue recorded in ny ptient with norml bioprosthesis. Although this mesurement could hve been in error, the outflow region of the left ventricle my ctully hve been nrrowed, either by postopertive tissue ingrowth, improper suture plcement or other problems relted to vlve implnttion. Becuse the ptient ws symptomtic, determintion of subvlvulr nd vlve res by crdic ctheteriztion ws not deemed cliniclly pproprite ; consequently, it is uncertin whether the noninvsive findings re erroneous or reflect mild subvlvulr stenosis. As ws the cse in erlier studies (8,23), mny (42%) of our ptients with cliniclly norml nd recently implnted prosthetic vlve hd mild ortic regurgittion by Doppler study. Our mesurements of left ventriculr outflow trct velocities demonstrted no difference between ptients with nd without regurgittion, thus confirming tht the volume of regurgitnt flow ws smll. Accurcy of noninvsive ortic bioprosthetic vlve re determintions. Prosthetic vlve res computed from echocrdiogrphic nd Doppler mesurements by ppliction of the continuity eqution were ccurte nd highly correlted with re determintions bsed on crdic ctheteriztion dt. Of the two terms tht contribute to the continuity eqution computtion, the rtio of subvlvulr to trnsvlvulr velocity time integrls ws considerbly more importnt in the reltion between noninvsive nd invsive vlve res thn ws the left ventriculr outflow trct dimeter, which dds only mrginlly to the correltion. Otto et l. (6) reched similr conclusion in their study of ntive ortic vlve stenosis, reporting tht velocity time integrl rtio of :so.3 (similr to our vlue of.35) ccurtely identified ptients with n ortic vlve re!5 1. cm 2. Two fctors ccount for the limited Woortnce of outflow trct mesurements. First, these vlues re squred in vlve re clcultions, considerbly mgnifying the mesurement error of 1 to 2 mm inherent in two-dimensionl echocrdiogrphic distnce determintions. Second, these mesurements would not be expected to ccurtely differentite mong the >85% of our ptients who hd prosthetic vlve with dimeter differing from tht of other ptients by ±2 mm. As result, the subvlvulr re term could be neglected without mterilly impiring our bility to estimte prosthetic vlve re noninvsively. Use of the mnufcturer's specified vlve dimeter in the continuity eqution impired the correltion between invsive nd noninvsive determintions of prosthetic vlve re. This finding implies tht the size of the subvlvulr region in ptients with prosthetic ortic vlve is not dequtely estimted by the sewing ring dimeter. The re proximl to the vlve my be nrrowed by the ortic nulus, fibrosis or grnultion tissue in some ptients, wheres subvlvulr diltion my be present in others. Of the eight ptients in our ctheteriztion cohort with moderte or severe ortic regurgittion by ngiogrphic estimte, six (75%) hd concomitnt prosthetic vlve stenosis. Left ventriculr outflow trct velocity ws significntly greter in these 8 ptients thn in the remining 14 ptients with to I+ regurgittion, reflecting the incresed systolic flow required to mintin dequte forwrd crdic output in the fce of substntil regurgittion. The impct of ortic regurgittion on the ccurcy of the continuity eqution, if ny, could not be determined becuse of the smll number of ptients with significnt regurgittion. Aortic bioprosthetic vlve stenosis. Echocrdiogrphic imging lone ws reltively insensitive in its bility to suggest dignosis of bioprosthetic ortic stenosis. In only 4 of our 12 ptients were thickened leflets with obviously restricted motion identified. Addition of continuous wve Doppler dt improved our bility to ident : fy the ptients with vlvulr sten6is. Accelertion time nd pek grdient tended to be greter in ptients with prosthetic vlve stenosis thn in ptients with norml vlve, but there ws imperfect seprtion between the two groups. Computtion of men pressure grdient improved the overll dignostic ccurcy to 98%. Although men pressure grdient ws n excellent predictor of prosthetic ortic stenosis in this study. this vrible will tend to be insensitive in ptients with depressed crdic output. Accordingly, estimtion of vlve re by the continuity eqution or by the rtio of left ventriculr outflow trct to trnsvlvulr velocity time integrls is preferble. This ltter Doppler vrible identified ll ptients in our study with nd without prosthetic vlve stenosis. Study limittions. Appliction of the continuity eqution to the clcultion of ortic vlve re from echocrdiogrphic nd Doppler mesurements demnds high degree of technicl skill. Use of this technique by investigtors without dequte trining might seriously compromise ccurcy. Becuse the left ventriculr outflow trct dimension is squred in the clcultion of ortic vlve re-_ smll errors in this mesurement cn produce substntil inccurcy in vlve re estimtes. A mesured difference of only 2 mm in n ortic nullis with dimeter of 2 mm will result in 19% difference in the vlve re clcultion.

8 824 ROTHBART ET AL. JACC Vol. 15, No. 4 Mrch 15, 199: Becuse few vlves with n externl dimeter <23 mm re implnted in ptients in our institutions, our experience with smller bioprosthetic vlves is limited. Were more such ptients vilble, we might hve observed greter overlp of Doppler vribles between normlly functioning smll prosthetic vlves nd lrger stenotic vlves. The Doppler criteri optimizing differentition between the norml group nd the group with stenosis were selected retrospectively. A prospective evlution will be needed to dequtely evlute the ccurcy of the techniques described here. Finlly, in this study, we compred Doppler findings in two types of ptients selected to mximize the differences between them : those with n pprently norml vlve nd those with proved stenosis ; symptomtic ptients whose ortic vlve replcement occurred >2 yers before their echocrdiogrphic studies were excluded. Hoffmn et l. (24) serilly exmined such ptient's with Doppler ultrsound nd reported progressive increses in trnsvlvulr grdient, which my reflect grdul decrese in vlve re over time. Such ptients should be included in future studies to ssess the bility of these noninvsive techniques to differentite mild from criticl prosthetic vlve stenosis. We express our pprecition to Mrie Prdo for ssistnce in preprtion of this mnuscript nd to Dine Amos for rtwork nd photogrphy. References I. Stmm RB. Mrtin RP. Quntifiction of pressure grdients cross stenotic vlves by Doppler ultrsound. J Am Coll Crdiol 1983 :2: Currie PJ, Sewrd JB. Reeder GS. et l. Continuous-wve Doppler echocrdiogrphic ssessment of severity of clcific ortic stenosis : simultneous Doppler-ctheter correltive study in 1 dult ptients. Circultion 1985 :71 : Kelly TA, Rothbrt RM, Cooper CM, Kiser DL, Smucker ML, Gibson RS. Comprison of outcome of symptomtic to symptomtic ptients older thn 2 yers of ge with vlvulr ortic stenosis. Am J Crdiol 1938 :61 : Teirstein P, Yeger M. Yock PG, Popp RL. Doppler echocrdiogrphic mesurement of ortic vlve re in ortic stenosis : noninvsive ppliction of the Gorlin formul. J Am Coll Crdiol 1986 :8 : Skjerpe T, Hegrenes L, Htle L. Noninvsive estimtion of vlve re in ptients with ortic stenosis by Doppler ultrsound nd twodimensionl echocrdiogrphy. Circultion 1985 :72 : Otto CM, Perlmn AS. Comess KA, Remer RP, Jnko CL, Huntsmn LL. Determintion of stenotic ortic vlve re in dults using Doppler echocrdiogrphy. J Am Coll Crdiol 1986 :7 : Gross CM, Wrm LS. Doppler echocrdiogrphic dignosis of porcine bioprosthetic crdic vlve mlfunction. Am J Crdiol l984;53: Sgr KB, Wnn LS, Pulsen WHJ, Romhilt DW. Doppler echocrdiogrphic evlution of Hncock nd Bjork-Shiley prosthetic vlves. J Am Coll Crdiol 1986 ;7 : Willims GA, Lbovitz AL Doppler hemodynmic evlution of prosthetic (Strr-Edwrds nd Bjork-Shiley) nd bioprosthetic (Hncock nd Crpentier-Edwrds) crdic vlves. 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Circultion 1985 ;72 : Johnson A, Thompson S, Viewig WVR, Dily P, Oury J, Peterson K. Evlution of the in vivo function of the Hncock porcine xenogrft in the ortic position. J Thorc Crdiovs Surg 1978 ;75 : Morris DC, King SB, Dougls JS, Wickliffe CW, Jones EL. Hemodynmic results of ortic vlvulr replcement with the porcine xenogrft vlve. Circultion 1977 ;56: Reisner SA, Meltzer RS. Norml vlues of prosthetic vlve Doppler echocrdiogrphic prmeters : review. J Am Soc Echo 1988 ;1 :21-1. '.9. Agtston AS, Chengot M. Aswth R, Hildner F, Smet P. Doppler dignosis of vlvulr ortic stenosis in ptients over 6 yers of ge. Am I Crdiol 1985 :56 : Htle L. Angelsen BA, Tromsdl A. Noninvsive ssessment of ortic stenosis by Doppler ultrsound. Br Hert J 198 ;43 : Czer LSC, Gry RJ, Btemn TM, et l. Hemodynmic differentition of pthologic nd physiologic stenosis in mitrl porcine bioprostheses. J Am Coll Crdiol 1986 ;7 : Ubgo JL, Figuero A, Colmn T, Ochteco A. Durn CG. Hemodynmic fctors tht ffect clculted orifice re in the mitrl Hncock xenogrft vlve. Circultion 198 ;61 : Goldrth N, Zimes R, Vered Z. Anlysis of Doppler-obtined velocity curves in functionl evlution of mechnicl prosthetic vlves in the mitrl nd ortic positions. J Am Soc Echo 1988 ;1 :21 ` Hoffmn A, Dubch P, Burckhrdt D. Evlution of ioprosthetic degenertion by Doppler echocrdiogrphy (bstr). Circ.?dtion 1987 ;76(suppl IV) :IV-45.