Accurate measurement of mitral annular area by ... - Semantic Scholar

European Heart Journal – Cardiovascular Imaging (2012) 13, 605–611 doi:10.1093/ejechocard/jer300

Accurate measurement of mitral annular area by using single and biplane linear measurements: comparison of conventional methods with the three-dimensional planimetric method Eiichi Hyodo 1*, Shinichi Iwata 1, Aylin Tugcu 1, Yukiko Oe1, Agnes Koczo 1, Kenei Shimada 2, Takashi Muro2, Junichi Yoshikawa3, Minoru Yoshiyama 2, Linda D. Gillam 1, Rebecca T. Hahn 1, Marco R. Di Tullio 1, and Shunichi Homma 1 1 Department Cardiology Division, Columbia University Medical Center, 622 West, 168th Street, PH3-133, New York, NY 10032, USA; 2Internal Medicine and Cardiology, Osaka City University Medical School, 1-4-3 Asahimachi, Abenoku, Osaka 545-8585, Japan; and 3Department of Cardiology, Nishinomiya Watanabe Hospital, 3-25 Ikedacho, Nishinomiya, 662-0911, Japan

Received 12 October 2011; accepted after revision 6 December 2011; online publish-ahead-of-print 30 December 2011

Aims

The planimetry method using three-dimensional (3D) echocardiography is useful for providing an accurate mitral annulus area (MAA) value. However, this method is relatively unavailable. Therefore, we evaluated the accuracy of conventional methods for MAA measurement compared with that of 3D planimetry. ..................................................................................................................................................................................... Methods Two-dimensional (2D) and 3D transoesophageal echocardiography (TEE) were performed in 70 patients. The mitral annulus diameter (MAD) was measured using four standard TEE imaging planes: four-chamber (4Ch), two-chamber and results (2Ch), anterior –posterior (LAX), and commissure–commissure (CC). MAA was calculated using a single diameter based on that of a circle and using two diameters based on that of an ellipse. MAA measurements using the single 4Ch MAD method (r ¼ 0.84, P , 0.001), and two anatomically orthogonal MAD method in 4Ch/2Ch (r ¼ 0.93, P , 0.001) and LAX/CC (r ¼ 0.97, P , 0.001) planes correlated with 3D planimetric MAA measurements. Further analysis with Bland–Altman plots revealed that the LAX/CC MAD measurement exhibited the closest limits of agreement with the 3D planimetric MAA measurement. Notably, in patients showing an elliptical annulus shape, only LAX/ CC MAD, but not 4Ch or 4Ch/2Ch MAD, provided results comparable with those of 3D planimetric MAA measurements. However, in patients with a circular annulus shape, reliable MAA measurements can be achieved using either single 4Ch MAD or any biplane MAD. ..................................................................................................................................................................................... Conclusion Conventional LAX/CC MAD can be recommended for MAA measurements in a diverse patient population. This method is applicable as an alternative to the 3D planimetric method, regardless of the mitral annulus shape.

----------------------------------------------------------------------------------------------------------------------------------------------------------Keywords

Mitral annulus diameter † Mitral annulus area † Three-dimensional echocardiography

Quantification of mitral regurgitation (MR) by using echocardiography has prognostic significance in a variety of patient populations. In patients with functional/ischaemic MR1,2 as well as in those with degenerative MR,3 the effective regurgitant orifice area is an independent risk factor for cardiac and overall mortalities. Quantitative Doppler calculation of relative stroke volume can provide an

accurate assessment of the effective regurgitant orifice area in MR patients. However, this calculation is strongly dependent on the accuracy of determining the mitral annular area (MAA).4 – 6 Furthermore, precise knowledge of MAA is important for developing better annuloplasty ring prostheses, which are routinely used in mitral valve repair.7 Hence, it is crucial to measure MAA accurately.

* Corresponding author. Tel: +1 212 305 2267; fax: +1 212 342 3718, Email: [email protected] Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2011. For permissions please email: [email protected]

606 Three-dimensional (3D) echocardiography using the 3D planimetric method can be used to measure MAA accurately8 – 10 and to improve understanding of the shape of the mitral annulus in patients with and without mitral valve disease.11 – 14 However, because of limited accessibility and financial constrains, conventional methods of MAA measurements that are as efficient as 3D planimetry should be explored. Kaplan et al.15 showed that the conformation of the mitral annulus is more elliptical than circular. However, the American Society of Echocardiography Guidelines advocate the use of single four-chamber (4Ch) mitral annulus diameter (MAD) based on that of a circle to estimate the MAA;6 this can lead to oversimplification.6,16 Therefore, the complex shape of the annulus should be taken into account when conducting single plane measurements for determining MAA.5 We aimed to elucidate which conventional methods have similar efficiency to that of the 3D planimetric method for MAA measurement and whether the conventional methods are affected by the mitral annulus shape.

Methods Study population Between July 2009 and July 2010, a total of 78 consecutive patients who have undergone both 2D and 3D transoesophageal echocardiography (TEE) were selected as study subjects. Clinical indications for TEE included aortic valve stenosis (n ¼ 24), mitral valve regurgitation (n ¼ 24), cerebral infarction (n ¼ 14), aortic valve insufficiency (n ¼ 9), atrial septal defect (n ¼ 5), and myxoma (n ¼ 2). Written

E. Hyodo et al.

consent was obtained from all subjects. This study was approved by the institutional ethics committee of our hospital.

TEE and transthoracic echocardiography Images were acquired using an iE 33 ultrasound system (Philips Medical System, Andover, MA, USA) equipped with a fully sampled 3D matrixarray transducer for TEE and a high-frequency transducer (S5-1) for 2D transthoracic echocardiography. The 4Ch, two-chamber (2Ch), anterior – posterior (LAX), and commissure– commissure (CC) axis measurements of the mitral annulus were obtained using 2D TEE from mid-oesophageal views. The 4Ch axis measurement of the mitral annulus was made in the 4Ch view at the hinge-point of the leaflets and the left atrium (Figure 1) such that the aorta was not visible from this view. The 2Ch axis measurement of the mitral annulus was made in the 2Ch view at the hinge point of the leaflet and left atrium such that the right side of the heart or the aorta was not visible (Figure 1). The CC diameter was measured from the CC view that shows three ‘humps’ (P1, A2, and P3) of equal sizes, which can be easily attained at a transducer rotation plane of 55708 (Figure 1).17 The MAD was measured at the hinge-points of the P3 and P1 scallops. The LAX view of the mitral annulus was obtained by rotating the beam angle clockwise to 908 from the CC view (Figure 1) to an imaging plane ranging from 145 to 1608; this producing a clear image of the aorta and the aortic valve opening. The location of the mitral annulus was defined at the hinge-point of the mitral leaflet and left atrium posteriorly, and the mitral leaflet and intervalvular fibrosa anteriorly. MAA with 2D diameters was calculated using the following equation: MAA = p

r 2 2

,

Figure 1 Reference image showing four-chamber (4Ch), two-chamber (2Ch), commissure– commissure (CC), and anterior– posterior (LAX) axes in relation with the mitral annulus (upper) and measurements of the 4Ch, 2Ch, CC, and LAX axes diameters using two-dimensional transoesophageal echocardiography (lower). Ao, aorta; A1, anterolateral segment; A2, anteromiddle segment; A3, anteromedial segment; noncoronary, non-coronary cusp of aortic valve; left, left coronary cusp of aortic valve; P1, posterolateral segment; P2, posteromiddle segment; P3, posteromedial segment; right, right coronary cusp of the aortic valve.

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Accurate measurement of mitral annular area

where r is the diameter of the circle; or MAA =

pr1 r2 , 4

where r1 and r2 are the diameters of the ellipse. To obtain images of entire mitral annulus, 3D images of the mitral valve were acquired using either the full-volume acquisition method or real-time 3D zoom mode (Figure 2). The images were acquired at a median volume rate of 22 Hz (range, 14 – 30 Hz) and analysed using the QLAB Mitral Valve Quantification software (MVQ version 7.0; Philips Medical System, Andover, MA, USA). In a series of 2D sections obtained from the 3D data, the operator defined both the annulus and commissures and traced the leaflets. The MVQ program then generated the valve model. Standard 3D planimetric MAA was quantified automatically by using this software (average measuring time, 22 + 5 min). According to the guidelines of the American Society of Echocardiography,6 all 2D and 3D TEE data were measured in early to mid diastole, one frame after the leaflets began to close. The MAA calculated using 2D diameters, including anatomically orthogonal imaging, was compared with those measured using the 3D planimetric method. Standard transthoracic 2D echocardiogram of the left ventricle was acquired using the parasternal long-axis view. The ejection fraction was

calculated using the modified Simpson’s method of discs.18 The severity of MR was evaluated as trivial, mild, moderate, and severe by using the ratio of the colour flow jet area relative to the left atrial size, according to the recommendations of the American Society of Echocardiography.19 The average values for both TEE and transthoracic echocardiographic measurements over three cardiac cycles were calculated. All analyses were performed by an experienced operator blinded to the clinical data. Inter-observer and intra-observer variabilities for MAD values using 2D images were determined for 15 randomly selected patients. Interobserver variability was calculated as a standard deviation of the differences in measurements done by two independent observers who were blinded to the patient data. Intra-observer variability was calculated as a standard deviation of the differences between the first and second measurements (2-week interval) done by a single observer.

Statistical analysis Continuous variables were expressed as mean value + SD values. Comparisons of the continuous variables between the two groups were performed using the unpaired t-test. Intra-group comparisons of MAA measurements were made using the paired t-test. Correlations between 3D planimetric MAA and MAA estimated using 2D diameters were assessed using linear regression analysis and Pearson’s correlation

Figure 2 Three-dimensional (3D) morphological analysis of a patient with mitral regurgitation. Mitral annulus is manually initiated in one plane (upper left) and then repeated in multiple rotated planes and interpolated (lower left). The resultant 3D-rendered valve model is shown in the lower right. The mitral annulus area was 11.7 cm2, according to the MVQ software.

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Table 1

Calculation of mitral annular area

MAA (cm2) measurement

All patients (n 5 70)

EMA group (n 5 36)

CMA group (n 5 34)

P-value

............................................................................................................................................................................... 3D planimetry LAX and CC diameter ratio Circle-based

7.5 + 2.1

7.7 + 1.8

7.2 + 2.3

0.25

0.84 + 0.11

0.76 + 0.06

0.93 + 0.09

,0.001

4Ch diameter

7.4 + 2.5

7.6 + 2.0

7.2 + 2.9

2Ch diameter LAX diameter

8.0 + 2.6* 6.1 + 1.9*

8.3 + 2.3* 5.7 + 1.4*

7.8 + 3.0* 6.6 + 2.2*

0.40 ,0.05

CC diameter

9.0 + 2.9*

10.0 + 2.4*

7.8 + 3.1*

,0.001

0.48

Ellipse-based Orthogonal planes 4Ch/2Ch diameters

7.6 + 2.4

7.8 + 2.0

7.4 + 2.8

0.45

LAX/CC diameters Non-orthogonal planes

7.4 + 2.2

7.6 + 1.8

7.1 + 2.5

0.45

4Ch/CC diameters

8.1 + 2.6*

8.8 + 2.1*

7.4 + 2.8

0.02

4Ch/LAX diameters 2Ch/CC diameters

6.7 + 2.0* 8.5 + 2.7*

6.6 + 1.6* 9.1 + 2.2*

6.8 + 2.4 7.8 + 3.0*

0.62 0.04

2Ch/LAX diameters

7.0 + 2.2*

6.9 + 1.8*

7.1 + 2.5

0.68

Data expressed as mean + SD values. *P , 0.05, compared with MAA obtained by 3D planimetry. CC, commissure– commissure; CMA, circular mitral annulus shape; EMA, elliptical mitral annulus shape; 4Ch, four-chamber; LAX, anterior –posterior; MAA, mitral annulus area; 3D, three-dimensional; 2Ch, two-chamber.

coefficient. Differences in correlation coefficients were evaluated using the conventional-dependent sample test.20 Comparisons between the MAA measurements obtained using 3D planimetry and 2D methods were assessed using the Bland – Altman plots. Differences were considered significant when the P-value was ,0.05.

Results Patient characteristics Out of the 78 patients selected for this study, those with mitral annular calcification (n ¼ 2), non-sinus rhythm (n ¼ 2), left bundle branch block (n ¼ 1), and technically inadequate echocardiographic images (n ¼ 3) were excluded from the study. The study was then performed using 70 patients (38 men; mean age, 72 + 18 years).

Comparison of the accuracy of various MAA measurements and 3D planimetric MAA measurement in all patients Among all the conventional methods used for MAA measurements, only three, namely, the single 4Ch plane and the paired 4Ch/2Ch and LAX/CC planes, were found to provide MAA values similar to that obtained using the 3D planimetric method (Table 1). Linear regression analysis showed that the LAX/CC planes based on an ellipse yielded the best correlation (LAX/ CC . 4Ch/2Ch . 4Ch, P , 0.01) (Table 2). Furthermore, Bland –Altman plots revealed that LAX/CC MAD values showed the closest limits of agreement for the MAA measurements (Figure 3).

Comparison of the accuracy of various MAA measurements and 3D planimetric MAA measurement in patients with elliptical and circular mitral annulus shapes To elucidate whether the mitral annulus shape is important for determining MAA, the patients were classified according to the mitral annulus shape, with an average LAX to CC diameter ratio of 0.84. Patients with a ratio ≤0.84 were classified into the elliptical group (EMA, n ¼ 36), and those with a ratio .0.84 were classified in the circular group (CMA, n ¼ 34). There were no significant differences in the age, gender, body surface area, or clinical comorbidities between the two groups (Table 3). Compared with the EMA group, the CMA group showed lower left ventricular (LV) ejection fraction, larger LV end-diastolic volume, and more severe MR. Both groups showed similar standard 3D planimetric MAA measurement values (Table 1). In the EMA group, the MAA values obtained using the single plane of 4Ch or the anatomically orthogonal 4Ch/2Ch and LAX/CC planes were significantly correlated with those obtained using the 3D planimetric MAA method in the order of LAX/CC planes, 4Ch/2Ch planes, and 4Ch plane (Table 2). Correlation of LAX/CC planes with the standard method showed that LAX/CC planes are applicable, regardless of the mitral annulus shape. However, 4Ch alone or the 4Ch/2Ch planes were clearly shape-dependent. Any other single plane measurement, except that of the 4Ch plane, resulted in MAA values that were either larger (2Ch and CC planes) or smaller (LAX plane) than that obtained using the 3D planimetric method. Similarly, MAA measurement

609


Table 2 Correlation between mitral annulus area (MAA) obtained using three-dimensional planimetry and MAA values obtained using different two-dimensional diameters MAA measurements (cm2)

All patients (n 5 70)

Ellipse shape (n 5 36)

Circle shape (n 5 34)

3D planimetry MAA Circle-based 4Ch diameter

R ¼ 0.84, P , 0.001

R ¼ 0.78, P , 0.001

R ¼ 0.87, P , 0.001

R ¼ 0.93, P , 0.001 R ¼ 0.97, P , 0.001

R ¼ 0.88, P , 0.001 R ¼ 0.97, P , 0.001

R ¼ 0.95, P , 0.001 R ¼ 0.97, P , 0.001

4Ch/CC diameters 4Ch/LAX diameters

— —

— —

R ¼ 0.95, P , 0.001 R ¼ 0.95, P , 0.001

2Ch/LAX diameters

—

—

R ¼ 0.93, P , 0.001

.............................................................................................................................................................................

Ellipse-based orthogonal planes 4Ch/2Ch diameters LAX/CC diameters Non-orthogonal planes

CC, commissure–commissure; 4Ch, four-chamber; LAX, anterior –posterior; MAA, mitral annulus area; 3D, three-dimensional; 2Ch, two-chamber; 2D, two-dimensional.

Figure 3 (A) Bland – Altman plots for comparing the mitral annulus area (MAA) values obtained using the three-dimensional (3D) planimetry and four-chamber (4Ch) axis mitral annular diameter (MAD) method. (B) Bland– Altman plots for comparing MAA values obtained using the 3D planimetry and 4Ch/2-chamber (2Ch) axes MAD method. (C) Bland– Altman plots for comparing MAA obtained using the 3D planimetry and anterior– posterior (LAX)/commissure– commissure (CC) axes MAD method. The closest limits of agreement were observed in the LAX/ CC axes for the MAA measurements, compared with those for other axes. using non-orthogonal pairs also resulted in significantly larger (4Ch/CC and 2Ch/CC planes) or smaller (4Ch/LAX and 2Ch/ LAX planes) MAA values. In the CMA group, only the 4Ch plane provided useful results with respect to single plane MAA measurement. Interestingly, all

biplanes, except for the 2Ch/CC planes, yielded values similar to those obtained using the 3D planimetric method. MAD measurements were confirmed to be reproducible and reliable with mean absolute differences of 4.9 + 3.0% (interobserver) and 4.6 + 2.8% (intra-observer).

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Table 3

Patient characteristics

Variable

EMA group (n 5 36)

CMA group (n 5 34)

P-value

................................................................................ Clinical characteristics Age (years)

73 + 19

72 + 17

0.74

Men Body surface area (m2) Hypertension

20 (56%) 1.9 + 0.3

18 (53%) 1.9 + 0.2

0.34 0.90

23 (64%)

22 (61%)

0.94

Diabetes mellitus

8 (22%)

9 (26%)

0.68

Hyperlipidaemia Known coronary artery disease Echocardiography

17 (47%) 13 (36%)

13 (38%) 14 (41%)

0.60 0.50

LV end-diastolic volume (mL)

124 + 30

117 + 36

0.42

LV end-systolic volume (mL)

49 + 16

60 + 27

0.04

49 + 11

,0.01

LV ejection fraction 61 + 8 (%) Mitral regurgitation grade Trivial

23 (64%)

10 (30%)

,0.01

Mild Moderate and severe

10 (27%) 3 (8%)

12 (36%) 12 (35%)

0.41 ,0.01

Data are expressed as mean + SD or number (percentage) values. CMA, circular mitral annulus shape; EMA, elliptical mitral annulus shape; LV, left ventricular.

Discussion Three-dimensional echocardiography using the 3D planimetric method can be used to measure MAA accurately8 – 10 and to improve the understanding of the shape of the mitral annulus in patients with and without mitral valve disease.11 – 14 Despite the advantages of 3D TEE, issues such as accessibility and financial issues still exist. Therefore, to re-evaluate the conventional methods that could measure up with the 3D planimetric MAA method is to be explored. Evaluation of all the conventional methods for MAA measurement revealed that only the orthogonal imaging planes of LAX/ CC and 4Ch/2Ch and the single plane of 4Ch could yield MAA measurements similar to that obtained using the 3D planimetric MAA method, regardless of the shape of the mitral annulus. Interestingly, among the three methods, LAX/CC planes were found to be the most accurate method for measuring MAA without the influence of the annular shape. This could be attributed to the low LAX/CC diameter ratio of the orthogonal plane; the LAX plane yielded a short axis and the CC plane yielded a long axis, representing the true anatomic major and minor axes of the mitral annulus. These findings suggest that conventional LAX/CC plane measurements are the best alternative to standard 3D planimetric MAA measurements in the general population. Sadik et al.21 showed that, in healthy subjects, the mitral stroke volume measured using LAX/CC MAD values based on an ellipse correlated

with the LV stroke volume to a greater extent than that measured using the 4Ch MAD value. Likewise, using 4Ch/2Ch and 4Ch MAD for healthy subjects, Pu et al.22 showed that 4Ch/2Ch MAD value based on an ellipse provides a more accurate MAA than the circular method that used 4CH MAD value with the thermodilution method as a standard. Although these studies emphasized that the elliptical shape of the annulus is critical for determining MAA calculation, whether such calculations can be applicable to patients with altered annulus shapes still remains to be explored. In fact, extending these studies by including all possible measurements of MAA, we had proven that elliptical-based orthogonal-imaging planes but not circular-based, particularly the LAX/CC MAD method, are better alternatives of the 3D planimetric MAA irrespective of whether patients have cardiovascular disease. The mitral annulus is a complex, saddle-shaped structure that can be closely described as an ellipse.15 Accordingly, the current recommendation of the American Society of Echocardiography for using single 4Ch MAD based on that of a circle to calculate MAA is an over-simplification; this was observed when patients in our study were segregated according to the mitral annulus shape (Table 2).6,16 Analysis performed according to the mitral annulus shape inferred that the accuracy of single or biplane measurements is greatly influenced by annular shape, particularly when the measurements are performed using the 4Ch/2Ch or 4Ch alone MAD. It is noteworthy that MAA measurements using 4Ch/2Ch or 4Ch MAD are applicable only for circular mitral annuluses. A clear definition of the imaging planes in patients with elliptical mitral annuluses will help in the accurate measurement of MAA through the use of a conventional method. The approach presented in this study, i.e. the assessment of MAA using anatomically orthogonal LAX and CC imaging planes, can be used in several clinical conditions. Because of the prognostic significance of the calculations of MR volumes and effective regurgitant orifice area,1 – 3 the conventional method using LAX/CC planes offers the most accurate differentiation of the risks for patients with MR, when the standard 3D planimetric measurement method is not accessible. Moreover, MAA measurement can be obtained with this conventional method by using 2D imaging techniques, such as transthoracic echocardiography, TEE, multidetector cardiac CT, and cardiac magnetic resonance imaging. The simplicity of the conventional 2D method in calculating MAA grants further advantage against the 3D planimetric method, which required about 22 min shown in this study. Although this study paved the way to accurate MAA calculation, further large-scale studies are required to confirm our results to attest the generality of the LAX/CC plane method for MAA measurement. In addition, the timing of MAA measurement should be evaluated. Although MAA was measured in early to mid-diastole in this study, the annulus shape varies during the cardiac cycle, which may affect the accuracy of MR severity quantification by using the calculated MAA value. However, the elliptical shape is maintained relatively well during diastole,15 and this may not be a significant issue for the assessment of MR severity. The standard 3D planimetric MAA was measured by using QLAB Mitral Valve Quantification software, which does not take into account the saddle shape of the mitral annulus in all its complexity. Whether or not the LAX/CC MAD method can be applicable to the saddle-


shaped mitral annulus is another issue that need to be attended.23 Nevertheless, the standard 3D method used in this study is so far the best among currently available methods in the clinical settings.

Conclusions The present study shows that among all the conventional methods evaluated, the elliptical-based MAA measurements obtained using the LAX/CC method provides the value most similar to the standard MAA value obtained using the 3D planimetry method in a diverse patient population. Therefore, the use of LAX and CC MAD values based on that of an ellipse can also be recommended as a standard method for MAA measurement. Moreover, patients with heart disease can have mitral annuluses of varying shapes; therefore, appropriate determination of imaging planes is important for MAA measurement. Conflict of interest: none declared.

Funding This research was funded by the Columbia University Cardiology Division Research Fund.

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