British Heart Journal, 1977, 39, 839-843

Mitral valve closure indexEchocardiographic index of severity of mitral stenosisM. F. SHIU

From the Cardiac Department, St. Thomas's Hospital, London

A new echocardiographic index of mitral valve diastolic closure, based on the rate of diastolic apposition ofthe anterior and posterior mitral leaflet echoes, was measured in 40 patients with mitral stenosis. This mitralvalve closure index correlated highly significantly with the mitral valve orifice area (calculated from theGorlin formula) (r= 0.87). Correlation between the diastolic closure rate (based on the EF slope) and thecalculated valve area was poor (r=0.37).

It is proposed that the mitral valve closure index excludes movement extraneous to the mitral apparatusand expresses the actual rate of valve closure, thus asoiding some of the factors known to contribute to thepoor specificity of the diastolic closure rate. The better correlation of the mitral valve closure index with thecalculated valve orifice area makes it possible to assess the severity of mitral stenosis by echocardiogram withgreater accuracy and confidence.

The echocardiogram provides substantive evidenceof organic mitral valve disease when its presence isonly suspected or clinically undetected. It alsoprovides surgically important information on thethickness and pliability of the valve leaflets and sizeof the left ventricular outflow tract. In the assess-ment of the functional severity of mitral stenosis theechocardiogram has so far made no definite contri-bution. Several investigators (Edler, 1967; Effert,1967; Gustafason, 1967) proposed that the diastolicclosure rate based on the EF slope of the anteriorleaflet of the mitral valve reflects the severity ofmitral stenosis but, like others (Mary et al., 1973;Cope et al., 1975), we found it to be insensitive andoften misleading in individual patients. We reporthere a new index of mitral valve closure, derivedfrom the rate at which the anterior and posteriorleaflet echoes approximate, which correlates withthe severity of the mitral stenosis sufficiently wellto be of clinical value.

Methods

Forty patients with dominant mitral stenosis werestudied by cardiac catheterisation and echocardio-graphy. The mitral valve area was calculated usingthe Gorlin formula (Gorlin and Gorlin, 1951).Cardiac output was estimated by duplicate indo-cyanine green dye dilution curves. Direct left atrialReceived for publication 3 December 1976

pressure by the transeptal technique was obtainedin all cases and the mean mitral gradient over 10cycles was measured by planimetry of simultaneousleft atrial and left ventricular pressure recordings.Left ventriculography excluded significant mitralregurgitation in all cases.Echocardiograms were obtained with a Smith-

Kline Ekoline 20 Ultrasonoscope and a 7-5 cmfocused transducer with a frequency rate of 2-25MHz and recorded on a Cambridge Multichannelphotographic strip chart recorder. Particular carewas taken to record the mitral echo where theanterior leaflet excursion was maximal and wherethe posterior leaflet echo was continuously present.The diastolic closure rate (DCR) of the anteriormitral leaflet was measured by the standard method(Feigenbaum, 1972). The EF slope is generally asingle measurement when the anterior mitral leafletis recorded at the level of maximum excursion(Rodger and Sumner, 1975). Where biphasic move-ment is seen, we have taken the earlier slope assuggested by Ross (1972). The distance between theanterior and posterior mitral leaflet echoes wasmeasured at early (X1), and at end diastole (X2) inatrial fibrillation or at the point of minimal separa-tion in mid diastole in the presence of sinus rhythm.A mitral valve closure index (MVCI) was obtainedby dividing X1-X2 by the time (t) over which closurehad occurred and expressing it as a percentage of

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the initial leaflet separation, i.e.

MVCI= X ' x 100%t xX1

(Fig. 1). When the diastolic descent of both anteriorand posterior mitral leaflet echoes are strictly linear,the MVCI can be simply expressed as the differencetween the two diastolic closure rates divided by theinitial mitral leaflet separation i.e.

DCRa-DCRp

Results

In the 40 patients studied, the age ranged from 28to 69 years, with 31 women and 9 men. Twelvepatients were in sinus rhythm, and the remainderwere in atrial fibrillation. All degrees of severity ofmitral stenosis were encountered-the calculatedmitral valve area ranging from 04 cm2 to 3-8 cm2.The diastolic closure rate (EF slope) correlatedpoorly with the calculated valve area (MVA)(r=0-37) (Fig. 2). In the same patients, the correla-tion between the mitral valve closure index and thecalculated valve area was much better (r= 0-87(Fig. 3). The regression equation was MVCI=33MVA-12 (P<0-001). The patients were assignedinto three groups of severe, moderate, and mildstenosis in the same way as has been done byprevious investigators (Cope et al., 1975), withcalculated valve areas of < 13 cm2, 1'3 to 1 8 cm2,and > 1 8 cm2, respectively (Fig. 4). The mean

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Fig. 2 Relation between diastolic closure rate (DCR)and calculated mitral valve area in 40 patients withdomninant mitral stenosis. The correlation was poor withr= 0-37.

values of the mitral valve closure index for the threegroups were 13, 49, and 74, respectively, withhighly significant differences between the means:P < 0.001 both between severe and moderate, andsevere and mild, and P < 0 005 between moderateand mild stenosis.None of the patients with a mitral valve closure

index above 40 had severe stenosis. All the patientswith mild stenosis had a mitral valve closure indexover 50, though 6 of them could have been mis-diagnosed as severe mitral stenosis with diastolicclosure rates below 25 mm/s. This more sensitive

l ~-_'------~-_DCR-DCR

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Fig. 1 The mitral valve closureindex (MVCI) is calculated as

Xl-X2MVCI = x 100 %

Where X1 and X2 representanterior and posterior mitral leafletseparation in early (X,) and end(X2) diastole (or before atrialcontraction in cases of sinus rhythm,as here), and t-time, in seconds,between X1 and X2. Alternatively

MVCI DCRa - DCRp x100%x1

where DCRa and DCRp are thediastolic closure rate of the anteriorand posterior leaflet echo, respectively.

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Mitral valve closure index

0

0

Fig. 3 Relation between the mitralvalve closure index (MVCI) and mitralvalve area in the same 40 patients as inFig. 2. The correlation is highlysigmficant (r=0-87), the regressionequation being MVCI=33 MVA-12.

n=40r =0-87

0 lMitral valve area (cm2)

discrimination by the mitral valve closure index isalso seen in Fig. 5, which shows the echocardio-grams of 3 patients with severe, moderate, and mildstenosis (MVA 1.0 cm2, 1P5 cm2, and 2-0 cm2, re-

spectively), all of whom also had a diastolic closurerate below 20 mm/s. Their mitral valve closureindex were clearly different, being 10, 43, and 80,respectively, reflecting the different rates of truevalve closure.

Discussion

In the normal heart, the anterior and posteriormitral valve leaflets reach maximum separation in

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20-10- 13Fb gtLp<0.005JOJ_

Lp< 0.00IJMV area <l13cm2 1l3-1b8cm2 >1.8cm2

Fig. 4 Distribution of the mitral valve closure index(MVCI) in severe, moderate, and mild mitral stenosis.Mean values are shown in figures and bars, together withthe standard error. The P values of the differencesbetween the means are shown.

early diastole after which rapid closure occurs sothat they are virtually apposed in mid-diastole(Rushmer et al., 1956). This yields a mitral valveclosure index value of the order of several hundred(Fig. 6). By contrast, in mitral stenosis, a persistentgradient of pressure across the valve results in de-layed closure (Zaky et al., 1968). The reduction inthe rate of valve closure would be expected toreflect the severity of the mitral obstruction. In verysevere stenosis, the valve would remain fully openthroughout diastole, giving a mitral valve closureindex of zero.The diastolic movement of the anterior mitra

leaflet echo is thought to reflect both valve move-ment and movement of the ring, the latter beingprofoundly influenced by cardiac output, heart size,and left ventricular filling (Zaky et al., 1968). Withincreasing stenosis, diastolic closure rate reflectsleaflet movement less and ring movement more(Chakom et al., 1972), a fact which certainly con-tributes to the poor correlation between diastolicclosure rate and mitral valve area (Cope et al.,1975). Zaky et al. (1968) suggested that a reasonableestimate of valve closure can be made by sub-tracting the ring excursion from the diastolicclosure rate, but this presents practical difficultiesbecause with single beam echocardiograms simul-taneous recording of the two structures is notpossible. On the other hand, simultaneous anteriorand posterior mitral leaflet echoes can be obtainedin the majority of patients with mitral stenosis, andmeasurement of the rate of approximation of thetwo echoes would be expected to give actualclosure movement of the valve. The exclusion ofany movement extraneous to the mitral valveapparatus by this method of measurement may wellexplain the better correlation of the mitral valveclosure index with the calculated mitral valve area

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M. F. Shiu

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Fig. 5 Echocardiogram from 3patients with mitral valve areasof A, 1-0cm2, B, 1.5 cm2, andC, 2-0 cm2. The diastolic closurerate was below 20 in eachinstance, but the mitral valveclosure indices were A, 10, B,43, and C, 80, clearly denotingsevere, moderate, and mildstenosis respectively.

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compared with that of the diastolic closure rate.The effect of extraneous movement on the diastolicclosure rate is shown in the echocardiogram of apatient with severe stenosis (Fig. 7) in whom thediastolic closure rate varied 0 to 15 mm/s withsuccessive beats. The mitral valve closure indexwas zero in every beat because the posterior leafletecho was parallel to that of the anterior. The poorspecificity of the diastolic closure rate is particularlyimportant in patients with mild mitral stenosis.For example, a diastolic closure rate of less than25 mm/s has been suggested as indicating moder-ately severe mitral stenosis (Feigenbaum, 1972),yet 6 of our patients with calculated mitral valve area

ranging from 2-0 cm2 to 3-8 cm2 had a diastolicclosure rate below that value. A correct assessmentwas possible with the mitral valve closure indexsince this was above the severe stenosis range in allsix.We have found the mitral valve closure index to

be a reliable index of the mitral valve area through-out the whole range of mitral stenosis. A mitralvalve closure index of 20 or less was invariablyassociated with severe mitral stenosis, and mitralvalve closure index of over 80 excluded significantstenosis (mitral valve area > 1-8 cm2).

In conclusion, previous attempts to correlateechocardiographic indices with the severitv of

Fig. 6 Normal mitral echogramshowing rapid combined diastolicclosure movement of the anterior andposterior leaflets, giving a mitralvalve closure index of 500.

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Mitral valve closure index

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P . .j..fWW. -.*-.. -. ,. wu79hAb..t..L* 'U,' I-- .p.-w. . %b. .Ij.%J. h.

Fig. 7 Echocardiogram from apatient with severe mitralstenosis (MVA = 06 Cm2).The diastolic closure rate variedfrom 0 to 15 mm/s betweensuccessive beats despite no truevalve closure movement (i.e.MVCI=0) in each beat.

mitral stenosis have been unsuccessful and have notjustified the substitution of echocardiography forthe cardiac catheterisation in the preoperativeassessment of patients. In the study, we haveestablished that an index derived from the rate ofapposition of the mitral leaflet echoes expresses thefundamental haemodynamic disturbance in mitralstenosis. The index correlated highly significantlywith the calculated mitral valve area suggestingthat this non-invasive method of quantifying mitralstenosis is accurate and reliable.

I thank Dr. M. M. Webb-Peploe and Dr. B. S.Jenkins for their encouragement and advice on thepreparation of this paper.

References

Chakorn, S. A., Siggers, D. C., Wharton, C. F. P., andDeuchar, D. C. (1972). Study of normal and abnormalmovements of mitral valve ring using reflected ultrasound.British Heart Journal, 34, 480-486.

Cope, G. D., Kisslo, J. A., Johnson, M. L., and Behar, V. S.(1975). A reassessment of the echocardiogram in mitralstenosis. Circulation, 52, 664-670.

Edler, I. (1967). Ultrasoundcardiography in mitral valvestenosis. American J'ournal of Cardiology, 19, 18-31.

Effert, S. (1967). Pre- and post-operative evaluation of mitral

stenosis by ultrasound. American Jrournal of Cardiology19, 59-65.

Feigenbaum, H. (1972). Echocardiography. Lea and Febiger,Philadelphia.

Gorlin, R., and Gorlin, S. G. (1951). Hydraulic formula forcalculation of the area of the stenotic mitral valve, othercardiac valves, and central circulatory shunts. I. AmericanHeart Journal, 41, 1-29.

Gustafson, A. (1967). Correlation between ultrasoundcardio-graphy haemodynamics and surgical findings in mitralstenosis. American J7ournal of Cardiology, 19, 32-41.

Mary, D. A. S., Pakrashi, B. C., Wooler, G. H., and Ionescu,M. I. (1973). Study with reflected ultrasound of patientswith mitral valve repair. British Heart J'ournal, 35, 480-487.

Rodger, J. C., and Sumner, D. J. (1975). Measurement ofdiastolic dosure rate of normal mitral valve. British HeartJournal, 37, 504-513.

Ross, F. G. M. (1972). Ultrasonic investigation of the heart.In Ultrasonics in Clinical Diagnosis, p. 120. Ed. by P. N. T.Wells. Churchill Livingstone, Edinburgh and London.

Rushmer, R. F., Finlayson, B. L., and Nash, A. A. (1956).Movements of the mitral valve. Circulation Research, 4,337-342.

Zaky, A., Nasser, W. K., and Feigenbaum, H. (1968). Study ofmitral valve action recorded by reflected ultrasound and itsapplication in the diagnosis of mitral stenosis. Circulation,37, 789-799.

Requests for reprints to Dr. M. F. Shiu, CardiacDepartment, St. Thomas's Hospital, LondonSE1 7EH.

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