Echocardiography in mitral stenosis

Abstract

Echocardiography plays a major role in diagnosis, etiology and severity of Mitral Stenosis (MS), analysis of valve anatomy and decision-making for intervention. This technique has also a crucial role to assess consequences of MS and follow up of patients after medical or surgical intervention. In this article we review the role of conventional echocardiography in assessment of mitral stenosis and future direction of this modality using 3D echocardiography.

1. Introduction

In normal cardiac physiology, the mitral valve opens during left ventricular diastole, to allow blood to flow from the left atrium to the left ventricle. This flow direction will be maintained as long as the pressure in the left ventricle is lower than the pressure in the left atrium and the blood flows down the pressure gradient.

Mitral stenosis (MS) is a mechanical obstruction in blood flow from the left atrium to the left ventricle. Obstruction happens due to thickening and immobility of the leaflets, thickening and fusion of the chorda tendinae or mitral annular and commissural calcification. The normal area of the mitral valve orifice is about 4–6 cm² when the mitral valve area goes below 2 cm², the valve causes an impediment to the flow of blood into the left ventricle, creating a pressure gradient across the mitral valve. This gradient may increase by the rise in heart rate or cardiac output. When the mitral valve area becomes less than 1 cm², there will be an increase in the left atrial pressure to overcome the valve gradient. This rise in the left atrial pressure is then transmitted to the pulmonary vasculature and causes pulmonary hypertension and eventually pulmonary congestion and edema.

Mitral stenosis consists of 12% of all valvular heart disease in Euro Heart Survey. Etiology of MS in adult patients in the great majority of cases (more than 90%) is the rheumatic involvement of the mitral valve. Other etiologies such as infective endocarditis, mitral annular calcification in elderly patients, congenital malformation (parachute mitral valve), systemic lupus erythematosis, carcinoid heart disease, endomyocardial fibrosis and rheumatoid arteritis are representing less than 10% of adult cases.

2. Diagnosis of MS-

2.1. Transthoracic 2D – echocardiography

Mitral valve assessment with echocardiography should include the pattern of valve involvement and calcification, severity of stenosis, associated mitral regurgitation and other co-existent valve lesions and atrial chamber dilatation and function. Mitral stenosis can be assessed in parasternal, apical or subcostal views. As with any stenotic valve the main diagnostic feature in the parasternal long axis view (Fig. 1) as in rheumatic MS, the anterior mitral leaflet (AMVL) shows diastolic doming or hockey-stick shape. And the posterior mitral leaflet (PMVL) has restricted motion or is totally immobile. This doming is due to the reduced mobility of the valve tips compared to the base of the leaflets.

Figure 1.

Parasternal long axis view in diastole, showing diastolic doming (hockey-stick shape) of anterior mitral valve leaflet (AMVL) and thickened, restricted posterior mitral valve leaflet (PMVL). RV = right ventricle, LV = left ventricle, LA = left atrium.

Echocardiography can also adequately assess the Subvalvular apparatus changes such as thickening, shortening, fusion of chordal and calcification (Fig. 1). Color Doppler in this view with diastolic turbulence across the mitral valve confirms the diagnosis. On the other hand, Parasternal short axis view of the mitral valve is used to assess the leaflets thickening and fusion of commissures. The parasternal short axis view is also used to assess the mitral valve orifice area by planimetry of the mitral leaflets at the level of tips (Fig. 2).

Figure 2.

Parasternal short axis view of the mitral valve at the level of the tips to measure mitral valve area (MVA) by planimetry. (A) Prior to percutaneous balloon mitral valvuloplasty (PBMV), showing fused both commissures with MVA = 1.2 cm². (B) Same patient after PBMV, showing complete opening of the anterolateral commissure and partial opening of the posteromedial commissure. MVA = 2.0 cm².

3. Indices of stenosis severity

The Following are different means of measurements by echocardiography to assess the severity of MS, which are mandatory in all patients:

Planimetry of mitral valve at the level of the leaflets tips in parasternal short axis view (Fig. 2). This method is a very familiar technique by 2D echocardiography but the same method can also be used in 3D echocardiography en-face view of mitral valve (Fig. 9). However, newly developed QLAB software in 3D echo is now available for calculation of mitral valve orifice area which requires further validation (Fig. 10).

Figure 9.

3D TEE zoom-mode of mitral valve with severe rheumatic MS. (A) Left atrial (LA) view or surgical orientation, as surgeon will see the mitral valve in the operating room after opening the left atrium. Aorta is located anterior to the MV and left atrial appendage is oriented at the left side of surgeon. (B) LV view of mitral valve showing fish mouth of mitral orifice. Surgeon will not see this side of mitral valve except opening from aortic root. Note grid in the screen which can be used for measurements but still should be validated.

Figure 10.

Calculation of mitral valve area (MVA) by QLAB software implemented in the 3D echo machine. (A) Two orthogonal views of mitral valve are derived from a 3D zoom-mode acquisition of the mitral valve. After proper alignment of lines representing x, y and z axis, mitral valve orifice will appear and MVA can be traced. (B) MVA was traced in same patient of Fig. 9 and showed 1.1 cm². This software still needs validation.

Calculation of mitral valve area (MVA) by pressure half-time (P_1/2 t) should be done in an apical four chamber view using continuous wave Doppler (Fig. 3). Pressure half-time method is not valid immediately after percutaneous balloon mitral valvuloplasty (PBMV). MVA should be averaged in 3 consecutive beats and in case of atrial fibrillation in it should 5 beats.

Figure 3.

Calculation of the mitral valve area (MVA) by the method of pressure half-time (P_1/2t).

Mean pressure gradient across the mitral valve can be measured in apical views. Modal Doppler (most dense portion of the Doppler curve) should be used for calculation (Fig. 4). The gradient can be measured by tracing the dense outline of mitral diastolic inflow and the mean pressure gradient is automatically calculated. The severity can be assessed as mild (<5), moderate (5–10) and severe (>10).

Figure 4.

Continuous wave Doppler parallel to the mitral inflow in apical 4 chamber view to measure mean peak gradient (Mean PG) across the mitral valve. Measurements should be done in 3–5 consecutive beats and averaged.

Estimation of pulmonary artery systolic pressure and the right ventricular systolic pressure (RVSP) is necessary. It can be measured from tricuspid regurgitation velocity by Bernoulli equation (Fig. 5). RVSP can also be assessed during exercise in borderline cases.

Figure 5.

(A) Estimation of pulmonary artery systolic pressure (right ventricular systolic pressure) using TR velocity and gradient in short axis view in a patient with severe MS and severe pulmonary hypertension (B) Calculation of left atrial volume using method of discs (MOD) in apical 4 chamber view in same patient, showing severe increase of LA volume.

Consequences of mitral stenosis on other cardiac chambers such as left atrial dilatation, tricuspid regurgitation and also right ventricular function should be evaluated by echocardiography. Left ventricular function is usually intact in uncomplicated mitral stenosis.

4. Grading of mitral stenosis

In grading the severity of MS based on echocardiographic evaluation, the following recommendations by the EAE/ASE (Baumgartber et al., 2009) are the used standards of practice. Please refer to Table 1.

Table 1.

EAE/ASE recommendations for classification of mitral stenosis severity.

	Mild	Moderate	Severe
Specific findings
valve area (cm2)	>1.5	1.0–1.5	<1.0
Supportive findings
Mean gradient (mmHg)a	<5	5–10	>10
Pulmonary artery pressure (mmHg)	<30	30–50	>50

^aAt heart rates between 60 and 80 bpm and in sinus rhythm.

5. Percutaneous balloon mitral valvuloplasty (PBMV)

Percutaneous valvuloplasty was introduced by Inoue in 1984 and revolutionized the treatment of selected patients with MS. Suitability of mitral valve for PBMV is based on echocardiographic findings. Wilkins score (Wilkins et al., 1988 – Table 2) and Cormier score (Lung et al., 1996 – Table 3) are the most widely accepted criteria for pre-procedure selections. Transesophageal echocardiography (TEE) is a great tool to assess anatomy and morphology of mitral valve leaflets, commissures, chorda and subvalvular apparatus (Figs. 6 and 7). Pre-op TEE is mandatory to rule out left atrial clot prior to PBMV (Fig. 8). In short, the following are the factors which favor a successful PBMV; Thickening confined to valve tips, good mobility of anterior mitral valve leaflet, little chordal involvement, no more than ++mitral regurgitation, no left atrial thrombus and no commissural calcification.

Table 2.

Assessment of mitral valve anatomy according to the Wilkins score (Boston score).

Grade	Mobility	Thickening	Calcification	Subvalvular thickening
1	Highly mobile valve with only leaflet tips restricted	Leaflets near normal in thickness (4–5 mm)	A single area of increased echo brightness	Minimal thickening just below the mitral leaflets
2	Leaflet mid and base	Midleaflets normal, considerable thickening of margins (5–8 mm)	Scattered areas of brightness confined to leaflet margins	Thickening of chordal structures extending to one-third of the chordal length
3	Valve continues to move forward in diastole, mainly from the base	Thickening extending through the entire leaflet (5–8 mm)	Brightness extending into the mid-portions of the leaflets	Thickening extended to distal third of the chords
4	No or minimal forward movement of the leaflets in diastole	Considerable thickening of all leaflet tissue (>8–10 mm)	Extensive brightness throughout much of the leaflet tissue	Extensive thickening and shortening of all chordal structures extending down to the papillary muscles

Table 3.

Assessment of mitral valve anatomy according to the Cormier score.

Echocardiographic group	Mitral valve anatomy
Group 1	Pliable non-calcified anterior mitral leaflet and mild subvalvular disease (i.e. thin chordae >10 mm long)
Group 2	Pliable non-calcified anterior mitral leaflet and severe subvalvular disease (i.e. thickened chordae <10 mm long)
Group 3	Calcification of mitral valve of any extent, as assessed by fluoroscopy, whatever the state of subvalvular apparatus

Figure 6.

TEE long axis view of a patient with severe mitral stenosis, diastolic doming and hockey-stick shape of the anterior mitral valve leaflet (AMVL) and restricted posterior leaflet (PMVL). Subvalvular apparatus is thickened but is not calcified. Wilkins score of this valve is calculated about 8, indicating suitability for PBMV.

Figure 7.

Extensive calcification of mitral annulus and leaflets in a patient with severe rheumatic MS. (A) 2-D TEE view showing calcification on the leaflets and annulus extending to the base of left atrial appendage (LAA). (B) 3-D TEE, zoom-mode, surgical view of same patient, confirming these calcifications shown as bright echo densities.

Figure 8.

Pre-op TEE assessment done for a patient with severe MS, prior to percutaneous balloon mitral valvuloplasty (PBMV), showing severe smoke in left atrium (LA) and large clot in left atrial appendage (LAA). PBMV was canceled and medical treatment started.

6. 3D echocardiography

3D echocardiography, especially 3D TEE is a merging tool and is very promising to assess anatomy of mitral valve due to excellent location of mitral valve in relation with esophagus. 3D TEE can show en-face view of the mitral valve from left atrial and left ventricular side. Morphology of the mitral valve, degree of fusion of the commissures, area of mitral valve by QLAB software, result of the balloon valvuloplasty and mechanism of possible post balloon mitral regurgitation are the information which can be driven from 3D TEE (Figs. 9–12). This technique can be used in Catheterization Laboratory during PBMV and in the operation room during surgical correction of mitral stenosis.

Figure 11.

3D TEE zoom-mode acquisition of a patient with severe rheumatic mitral stenosis, viewing from LV side. (A) Prior to balloon valvuloplasty, mitral valve area (MVA) calculated by the grid and 3D QLAB was 0.7–0.8 cm². (B) Same view, 2 days after successful PBMV, both commissures are fully split. MVA calculated by same methods showed increasing to 2.1 cm².

Figure 12.

3D TEE, full volume color acquisition of mitral valve of patient with history of severe mitral stenosis who underwent balloon valvuloplasty one year ago and now presented with severe mitral regurgitation. (A) Full volume acquisition of mitral with color suppressed, showing over-spliting of both commissures . Anterolateral commissure (ALC) showed line of avulsion of this commissure towards A1 segment of anterior mitral leaflet. (B) Same view with color showed severe mitral regurgitation (MR) jet origination mostly from that avulsion and second jet from over-spliting posteromedial commissure (PMC).