Regurgitant Flow Rate Estimation Using Doppler Color Flow Imaging in Children with Mitral

(1)

Tiirk Kardiyo/ Dem

Arş

1997; 25: 200-205

Regurgitant Flow Rate Estimation Using Doppler Color Flow Imaging in Children with Mitral

Regurgitation

Vedide TAVLI, MD, Yasser AL-KHATIB, MD, Roberta G. WILLIAMS, MD, FACC, Ah Lin WONG, RDMS

From the Department of Pediatrics, Division ofCardiology, UCLA School of Medicine, Ca/ifomia, Los Angeles

ÇOCUKLARDA MiTRAL YETERSİLLİK JETİ AKIM HIZININ RENKLi DOPPLER

EKOKARDİOGRAFİ İLE DEGERLENDİRİLMESİ

Mitral

yetersizliğinin

(MY) Doppler ekokardiografi ile de- recelendirilmesinde

çeşitli

kantitatif metodlar

önerilmiş

tir. In vitro

^şartlarda

yeni bir metod olan proksimal

^eş

htzlı

hemisfer/erin yüzey ala m ( PISA) kullamlarak ak tm htztmn

doğrulukla ölçiilebildiği gösterilmiştir.

Aym pren- sibin renkli Doppler ekokardiografi ile klinikte de ku/lam- larak, belirli bir kan haciminin aktnı Jui11mı (cnı31sn) = P!SA (

^cmı)

x aliasing

^hızı

(

^cnılcn)

formii/ii ile hesaplana-

bileceği düşüniilmiiştiir.

MY olan çocuklarda bu

metodım

klinik

kullanınımı

belirleyen ilk

çalışma olması

nedeni ile bu

araşttrnıa yaptlnuşltr. Yaşlan

sekiz ay ile 12 ytl ara- smda (ortalama ; 3.1 yt!) olan 37 hasta

çalışmaya

dahil

edilmiştir.

PISA-Dopp/er ölçümleri ile kateterizasyon so- nuç/an arasmda

anlamlı

bir

ilişki saptanmtşttr

(r=0.93, p<O.OOO/ ). MY jet

alanınlll

sol atrium alanma oranttst anjiografik derecelendirme ile

karşt!aşttrtldtğtnda

yine anlarnit bir

ilişki bulunmuştur

(r=0.92 , p<O .OOOJ ). Ancak, anjiogra fi ile

karştlaşttrtldtğmda

PIS A metodu ile elde edilen sonuçlann jet al am oranttstna ktyas/a daha iyi bir korre/asyon

gösterdiği saptannuşttr.

Sonuç olarak, mitral kapak

yetersizliğinin

noninvaziv kantitatif derece/endiril- mesinde PISA metodu ile elde edilen sonuçlamt hastala-

mı

takibinde kul/ammilllll güvenilir

olduğu

kanaatine va-

nlmtşttr.

Anahtar kelime/er: Mitral yetersiz/ik, jet aktm hiZI,

eş /m/ı

hemisferlerin yüzey alam.

Over the recent years Doppler echocardiography has e merged as the noninvasive method of choise for con firming the diagnosis and severity of mitral re- g urg itation. Color flow mapping and calculation of regurgitant fraction have been the most widely studi- ed methods (1-5). A new method, which quantitates the proximal isove locity surface area (PISA), more

Adress for correspondence: Dr. V ed ide

Tavlı,

17

ı4

sokak,

ı

S/6

Karşıyaka-ızmir,

Tel.:

0-90-232-38ı ı649

Dr.Tavlı

was suppor!ed by a grant from Dokuz Eylül University School of Medic ine, I zmir.

The paper was prese nted at the 8th Nat.ional Congress of Cardiology.

Septeınber

27 - October

ı,

1 992, Istanbul

recently addressed as the flow convergence region (FCR), on

tl'ıe

left ventricular side has been invcsti- gated in only a few elinical studies

(6-ı ıı.

According to the hydrodynamic theory, flow approaches an ari - fice in a series of concentric hemispheric shells of increasing velocity known as the FCR. Doppler co- lar flow mapping of FCR may be accomplishcd once the blue-red aliasing radius is identified on the left ventricu lar side. Volume flow rate (ml/see) can be calculated as PISA (cm2) x aliasing velocity (cm/see). Flow calculations with this technique has been examined in vitro studies and seem to be lcss influe nced by technical factors and arifice shape which alter jet appearance

(ı2-ı8).

Recently the tech- nique was shown to allow in understanding the pat- hophysiology of the regurgitation

^(ll).

The purpose of this study is to carreiate the results of the PT SA and jet area methods to angiographic gradin g in a elinical setting.

MATERIALS and METHODS

Thi rty-seven patients, aged from eight months to 1 2 years (mean: 3. 1 years) w ith varying degrees of mitral regurgita- tion were included in the study. All of the patie nts wcrc in sinus rythm. The etiologly of the mitral regurg itation inc- lu ded residual mitral regurgitation present in Iate post-opc- rative pe riod following mitral annuloplas ty in 18

paticııts,

dilated congestive cardiomyopathy in nine patients, mitral valve prolapse in four patients, rheumatic carditis in s ix patients. Patients with arrhythmias, aortic valve disease, mitral stenosis, intra-cardiac shunts and eccentric rcgurgi- tant jets were excluded.

Angiographic grading was avai lable in all of t he

paticııts.

Cardiac catheterization was carried out a fter obtaining a

wriıten

consent a nd within 1-2 hours of the echocardiog-

raplıic

examination. Left

ventriculograplıy

was imal}ed in 60 degrees left anterior oblique and 20 degrees cranial and 45 degrees right anterior oblique projectian using lopro-

nıid

ata maximum total dose of 5 ml/kg. Qualitative a ng i-

ograplıic

grading was done into fo ur grades by an observcr

(2)

V.

Tavlı

ve ark.: Regurgitam

Floıv

Ra te Esrimation Us ing Doppler

ColorFioıv

lmaging in Children

wir/ı

Mitral Regurgirarion

blinded to the echocardiographic results. 1 + was regurgi- tant jet with minimum opacification of the

lefı

atrium which deared rapidly. 2+ w as regurgitant jet w ith m adera- te opacification of the left atrium which deared rapidly.

3+ when the left atrium was as intense as that of the left ventride and aorta on Iate films. 4+ when left atrium was more intense than that of the left ventride and aorta, and intense opacification persisted throughout the entire series of

fılms (19).

Echocardioraphic studies were done with Acuson XP-1 28 and 3 or 5 MHz transducers. The Nyqui st limit ranged from 43 to 64 cm/see. The gain !eve! was kept just below that which produced a noise in the color signal. The results were obtained in the apical four chamber and

parasterııal

long axis views. The radius of the proximal flow canver- gence region was measured at a point in

nıidsystole

from the first aliasing Iimit to the ventricular edge of the mitral leaflets ncarest to the regurgitant arifice and staying as pa- rallel as possible to the directian of the transducer in the apical four chamber view. The

measurenıents

were analy- zed using the Freeland computer system. The following equat ion was used to calculate the instantaneo us regurgi- tant flow where r= radius of the aliasing surface, NL=

Nyquist limit, Q= instantaneous flow in L/min

(7).

2nR

²

x NL x 60 Q=

1000

The

resultanı

value was subsequently indexed for body surface area.

Principle: S ince color Doppler is capable of showing spati- al relations of

lanıinar

flow reliably, the area of canver- gence region can be quantified. The aliasing boundary with a known velocity and a measurable radial distance from the cen ter of the arifice to the color change can be used to determine an isovelocity hemisphere. The zone of

proxinıal

flow acceleration is

nıade

up of concentric he-

nıispheric

shells of equal and accelerating velocities, the

snıallest henıisphere

being near the arifice having the hig- hest velocity. Fluid

dynanıics

theory states that the flow through any of these isovelocity surfaces is identical and equal to the velocity multiplied by the surface area. The velocity at which aliasing occurs multiplied by the calcula- ted first isovelocity surface area yields the instantaneous regurgitant flow rate.

Mitral regurgitation was also quantified by

nıeasuring

the jet area at its maximum turbuleni area both in the apical four chamber and parasternallong axis views. The results were expressed as an average of the ratio of jet area to the area of the left atrium in two orthogonal planes.

Fifteen randamly selected patients were analyzed by two observers blinded to the results. lnterobserver variability was meas ured for regurgitant flow rates. The radius of the proximal isovelocity surface was

nıeasured

by the same abserver on two

consecuıive

days to calculate the intraob- server variabi lity.

Statistics

Data are expressed as m ean± 1 SD. Differences

beıween

angiographic grades were expressed

wiıh

the use of

sıu

den t's

ı

test for unpaired data.

Spearnıan's

rank corrclation method was used to assess the assodation between the co- lor Doppler results and the

lefı venıricular angiograplıic

degree of mitral regurgitation. A comparison between ins-

tanıaneous

regu rg itant flow rate and jet area percentage was done by means of linear regrcssion analysis.

Conıpari

sons of

measurenıenıs

of

hearı

rates and blood pressures were made with student's t test for paircd valucs. The lcvcl of statistical signifi cance was defined at p<O.OS.

RESULTS

By angiog raphy, nine

patienıs

had 1+, ll had 2+, 14 had 3+ and four had 4+ mitral

regurgitaıion.

Thcrc was no statistically

significanı

differenccs in hcart rate or blood pressure obtained during the noninvasi- ve measurements and at the time of the

caıheıerizati

on (p>0.05). Regurgitant jet arca perccntagc, flow rate index, m ean aliasing radius and mcan Nyquist limit values obtained in the four angiographically- determined severity degrees of MR are

presenıed

in Table 1.

The relationship between the calculated

regurgitanı

flow rate us ing the PISA me thod

correlaıed

highly

Tab le 1. Regurgitant jet area percentage, fl ow ra te indices,

nıean

aliasing radius and

ınean

Nyquist li m i ts according to

angiognıphi·

cally

deternıined

degrees of severity of mitral

insuffıciency.

Angiograplıic

grading

1+ 2+ 3+ 4+

(n=9) p (n= ll ) p (n= l4) p (n=4)

Area%: 6.2±2.3 <0.001 9.04±2 <0.00 1 13.4±2.1 < 0.001 32±8.8

Regurgi tant

flow rate 3±1.3 <0.05 6.7±3.6 < 0.0001 14.9± 1.6 < 0.0001 34± 1 3.7

index:

(L/ınin/m2)

Mean aliasing

radius

(nı nı)

1.38±3.4 <0.05 3.5±1 < 0.05 7.5±2.4 < 0.05 11 .8±4.6

Mean Nyquist

liınit

(cm/see) 57±7 >0.05 53±7 > 0.05 52±0.8 >0.05 50±4.9

(3)

Tiirk Kareliyol Dem

Arş

1997; 25:200-205

Regurgilant jel area(%)

so _1-

r-=0.95 ₍

40~ p<0.0001 y=O Bx •2 ?5

30

20;¹

10~

o}-

o

¹⁰ ²⁰ ³⁰

PISA

Fig ı.

Correlation between

rcgurgitant flow ratc using the proxi-

mal isovelocity surface area (PISA) method on the x axis and ra-

tio

of color Doppler regurgitant jet arca on the y axis. (r: 09.95, p<O.OOOI)

significantly with the ratio of regurgitant jet area to left atrial area (Fig. 1).

\Vhen measures of instantaneous regurgitant flow ra- te were corrclated with an giographic grade of mitral regu rgitation, a correlation coefficient of r=0.93 (p<O.OOOl) was obtained with a

nıild

overlap betwe- en the groups (Fig. 2). The correlation between the ratio of jet area to left atrial area and the angiograp- hic grade of mitral regu rgitation w as significant w ith a correlation coefficient of r=0.92, {p<O.OOOI). The- re was mild overlap between the groups (Fig. 3).

The interobserver variability was 1.4 o/o± 3.9 o/o for calculated regurgitant flow rates. The intraobserver variability for the radius measurements was 0.6 ± 2.9 o/o (mean difference ± SO).

60·

50· r=0.93

40· p < 0.0001

p

ı 30·

s

A 20·

10·

GW

1 angiographic gradin~

Fig

2.

Boxplot showing comparison of color-tlow Doppler ima-

gcd instantaneous regurgitant tlow rate calculation for cach angi-

ographic grade of mitral regurgitation in

37 paticnts

. Standard de- viati

on values for each angiographic g

roup are slıown. Black are- as represent values between 25th and 75tlı

percentile

Angiographic grading

Fig 3. Corn~laıion showing comparison of the ratio of color now

Doppler rcgurgitant jet arca to left atrial arca calculatio

n w ith an- giograplıic grade of mitral rcgurgitation in

37 patients. Standani dcviation values for each angiographic group are

shown. 131ack arcas represent v;ılues

between 25th and 75th percent ile.

DISCUSSION

With the introduction of

two-dinıensional

color Doppler flow imaging, measu reme nts of jet

lcııgth,

width and area were used for the quantification of valvular regurgi tation ( 1,2). S ome authors have esri - mared I+ mitral regurgitation by echocardiography when the jet was located immedinrely posrerior to the mitral valve and 4+ when the flow was prcsent diffusely all over the atrium

(3),

Th is sort of grading faces problems when the regurgitan t jet is narrow and reaches the roof of left atrium. To minimize such problems, some authors have choscn to grade regurgitation as a fract ion of regurgitant a rca to lcft at ri al area ( 1.2).

Unfortunately , mcchanica l factors such as ga in, transmitted frequency, wall filter and pulsc rcpctiti- on frequency interfe re with accuracy of mitral regur- gitation quantification (20-40). Hemodynanıic factors including blood vi scosity, afrerload, preload, arifice area, regurgitant flvw ve locity and flow duration ha- ve been shown to effect Doppler color jet arca

(1,2,25,26). Analysis of the conve.·ging t1ow proxirnal to a restrictive arifice has been proposed as an a lter- native method in the quantification of fl ow ratc in regurgitant lcsions (13,14).

Ynınamura

et al. have previously reported that mini-

mum color encoded velocity area proximal ro the rc-

guritan t or ifice correlates well with angiographic se-

verity of m itral regurgitation

(27).

Later, minimum

(4)

V. Tavli ve ark.: Regurgitant Flow . '?at e Esrimation Us ing Doppler Co/or Flow lmaging in Children wir h Mitral Regurgitation

color encoded velocity area was s hown to be affec- ted by ultrasound machine factors , unlike the proxi- mal isovelocity aliasing surface (22). In vitro studies, the color aliasing radius was shown to correlate ext- remely well with the actual flow rate (r=0.99)

(14,1 7, 18).

In addi tion, this approach has the ad vanta- ge over other color Doppler methods in th at the PI- SA is apparently not affected by c hanges in machine factors

(7, 14-16).

In this study, PISA method was applied clinically for estimating regu rgitant volume flow in children with mitral regurgitation. The correlation of in stantaneous flow rate us ing the PISA method to the jet area-to- left atrial area ratio was significant with a correlation coefficient of r=0.95

(9)

(p<0.0001, Fig. 1). In our study population, a good correlation was observed between the jet area and angiographic degree of mit- ral regu rgitation (r=0.92, p<O.OO

ı,

Fig. 3). Helmcke et al

(ı)

have rcported a modest correlation (r=O. 78) in a nons imultaneous comparison bet ween angiog- raphi c grading and je t/left atrial area ratio. Later Spain et al

(2)

reported si milar results with a modcst correlatio n (r=0.76) betwee n maximal jet area and ani ographic grading, but in contrast to Helmcke et al

(1)

found no improv\!me nt in correlation when a ratio of jet size to left atrial area w as u sed (r=O. 7 1 ). The limitation regarding these s tudies was nons imultane- ity of color Doppler and angiography. The results observerd in our s tudy is better ( r=0.92), probably owing to the study design in which the patients were examined using diff erent techniques with close pro- ximity in timing.

Factors contributing to the disparity between

coıor

Doppi'er je t area and ang iography are technical fac- tors such as gain setting, depth and pul se repetition frequency

(28).

The distribution of jet area w ithin the le ft atrium is not uniquely dependent on the amount of regurgitation , but also on the

pı:c~Jsure

gradient between the chambers

(26).

Anather limitation in the analysis of jet area is eccentricit y of the jet which I e- ads to the unde restimation of the degree of the mitral regurgitation

(29).

Because the FCR is located in the hig h pressure chamb er, PlSA tec hnique appears to be independent of the directi on of the j et allowing for an accurate prediction of the severity of the re- gurgitation

(8).

The proximal FCR method has been s tudied several

times in compute r simulations and in in-vitro fl ow models

(12,14,17,18).

Until now elinica l experi ence with the PISA method has been limited

(8-1 1).

The principle of flow convergence was al so used in the assessme nt of shunt t1ow across a ventricular septal defect (6). In this study, s imilar to prev ious elinical studies there was a s ig nificant correla tion betwcen PISA-Doppler and cathe terization resu lts (r=0.93, p<O.OO

ı,

Fig. 2) . Bargiggia et al

(8)

have fo und a close conelation between the Doppler derived regur- g itant flow rate and angiographic degree of mitral regurgitation in 52 adults (r=0.9 1, p<O.OO 1). They also found a significant corrclation betwccn ang iog- raphic regurgitant- volume and flow calculated by Doppler (r=0.93, SEE: 123 ml/see)

(8).

Among seve- ral co mparis ons made in thci r study, Uts unomiya ct al

(7)

found s ignificant corrclation betwcen the mit ral regu rgitan t stroke volume us ing the PISA method and regurgit-ant jet area rat i o (r=0.84, p<O.OO

ı).

The formula they used was dcrivcd from prcv ious in- vit- ro studies, such that reg urgitant stroke volumc = 8.05 x r2, where r is the maximum alias ing radius and 8.05 is the constant. The authors have concluded that the constant 8.05 may not be a pplicable to all cases of mitral regurg itation

(7).

W e have u sed a sc- parate formula and found a better

coı-relation

bc twc- en th e instantane ous reg urgitant fl ow rate a nd jet area ratio (r=0.95, p<O.OOO

ı).

However, our number of patients were smaller.

Rivera et al (9) compared proximal FCR method to the regurgitant stroke volumc and regurgitant

fracıi

on calcul ated by pu lsed Doppler and found vcry go- od co rrelations for both compariso ns , r=0.93 and r=0.89, respectively.

Lowe r aliasing velocities using zero-baseli ne s hift

technique allows to detect the aliasing radius in pati-

ents with mild mitral regurgitation. Hence, care must

be taken to avoid inappropriate use of low alias vc lo-

cities whjch result in elongation of the a lias ing con-

tuor. Zero shi fting below 50 % of the Nyquist I im it

must be avoided

(1 1)_

The aliasing velocities in this

study ranged from 43 c m/see to 64 cm/see wh ich a l-

lowed for adequate visualizat ion of the proximal

FCR in all of the patients. Measuring the FC R radius

in the directian of the transducer wou ld execute ma-

jor problems in the cakulation of flow rates w ith co-

ni cal s haped aliasing zones. The size of the rcgurgi-

tant jet area was sho wn to vary during the regurgi-

(5)

Tiirk Kardiyol Dem

Arş

/997; 25:200-205

tant period

(1 1).

This fact may account for discrepan- cies between the Doppler and angiographic data. In our opinion, the good agreement between the instan- taneous regurgitant flow rate and angiographic gra- ding demonstrate that the limitations do not pose a major problem.

Despite its various limitations, left ventricular angi- ography is stili the most often used method of asses- sing the severity of mitral regurgitation. The sensiti- vity and specifity for the diagnosis of mitral valve repair or replacement of mitral regurgitat ion, using angiography as the gold standa rt were 100% and 93% by Doppler echocardioraphy as compared to 95% and 85% by elinical evaluation (3,30).

In conelusion, calculating mitral regurgitant flow ra- te from PISA provides excellent agreement wirh an- giography and has the advantage of being a non-in- vasive elinical method.

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(6)

V.

Tavlı

ve ark.: Regurgiwm Flow Ra re Esrimation Using Doppler Co/or

Floıv

lmaging in Children

wir/ı

Mitral Regurgirarion

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Düzeltme

26. Simpson JA, Valdez-Cruz LM, Sahn DJ, et al:

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25 . cilt 108- 11 3. sa yfal arında yayınlanan "Konjenit al Aort Darlıklarında Balon Valvüloplasti: Er- ken ve Orta Dönemli Sonuçlar" isimli yazıda , aşağıdaki düzeltmeleri yaparız.