|Year : 2017 | Volume
| Issue : 3 | Page : 197-205
How to assess mitral stenosis by echo - A step-by-step approach
Institute of Cardiology, Madras Medical College and Rajiv Gandhi Government General Hospital, Chennai, Tamil Nadu, India
|Date of Web Publication||12-Dec-2017|
Dr. Gnanavelu Ganesan
No. 7, Kanakkar Street, Tiruvottiyur, Chennai - 600 019, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Rheumatic mitral stenosis is the commonest valvular heart disease in developing countries. Other causes include congenital abnormalities and degenerative mitral valve disease. Mitral stenosis when it is due to rheumatic process, can be managed by percutaneous transvenous mitral commissurotomy. Echocardiography remains the most important investigation in diagnosing and planning the managemnt of mitral stenosis. This review highlights stepwise approach for comprehensive assessment of mitral stenosis by echocardiography.
Keywords: Mitral stenosis, pressure half time, rheumatic valve disease
|How to cite this article:|
Ganesan G. How to assess mitral stenosis by echo - A step-by-step approach. J Indian Acad Echocardiogr Cardiovasc Imaging 2017;1:197-205
|How to cite this URL:|
Ganesan G. How to assess mitral stenosis by echo - A step-by-step approach. J Indian Acad Echocardiogr Cardiovasc Imaging [serial online] 2017 [cited 2018 May 23];1:197-205. Available from: http://www.jiaecho.org/text.asp?2017/1/3/197/220534
| Introduction|| |
Mitral stenosis (MS) is the most common valvular heart disease encountered in developing countries. The cause of MS is almost always chronic rheumatic heart disease. Rarely, MS could be due to degenerative mitral annulus calcification and congenital abnormalities like single papillary muscle, mitral arcade, parachute mitral valve [Table 1] and [Figure 1]. Some of the extremely rare causes of MS include systemic lupus erythematosus, mucopolysaccharidosis, large vegetation, left atrial (LA) myxoma, and ball valve thrombus. The incidence of isolated MS is about 25%. Combined MS and mitral regurgitation (MR) account for 40% of cases. Associated aortic valve involvement is seen in 35% of cases.
|Figure 1: Upper panel: Parasternal long-axis view; Middle panel: Parasternal short-axis view; Lower panel: A4C view. Rheumatic mitral stenosis: Typical doming of pliable anterior mitral leaflet, fish mouth orifice, dilated left atrium with doming leaflets. Congenital mitral stenosis: Anterior mitral leaflet domes with eccentric location of orifice, Bulging interatrial septum to right; both leaflets attached to single-papillary muscle. Degenerative mitral stenosis: Dense calcification with restricted opening, spared commissures from calcification; dilated left atrium|
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| Objectives of Echocardiographic Assessment|| |
Echocardiography is the single most important diagnostic tool in the evaluation of MS. The objectives are:
- To confirm the etiology
- To assess the severity of stenosis
- To recommend the type and timing of intervention
- To assess other valvular lesions, presence of thrombus, and vegetation.
Chronic rheumatic activity results in commissural, cuspal, chordal, and combined changes in the form of fusion, thickening, and mobility restriction. All the modalities such as M-mode, two-dimensional (2D) echo, and Doppler evaluation should be used in the assessment.
Wilkins score [Table 2] and Padial score are particularly useful to assess the suitability for balloon mitral valvotomy (BMV) and predict MR following valvotomy.
|Table 2: Wilkins scoring system for mitral valve characteristics by echocardiography|
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| Step 1: Two-Dimensional Echocardiography|| |
The following parameters need to be assessed about the valve morphology:
- Subvalvar fusion
- Commissural fusion
Thickness of valve leaflet
Rheumatic activity increases the thickness and restricts mobility of mitral leaflets. Commissural fusion leads to doming of the anterior leaflet which gives “hockey stick appearance” [Figure 2]a.
|Figure 2: (a) Measuring thickness of the tip of anterior leaflet in diastole. (b) Objective measurement of leaflet mobility (ab/xy)|
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The normal thickness of mitral leaflet is 2–4 mm. Usually, thickness of mitral leaflets increases at the margins in MS and extend toward body and whole leaflet is thickened in severe cases. Depending on the thickness, four grades are given in Wilkins score. Mitral leaflet thickness can be compared to posterior aortic wall thickness, and the ratio gives an objective assessment. Normally, the ratio of valve thickness/posterior aortic wall thickness is <1.4. The ratio between 1.4 and 2.0 indicates mild thickening, the ratio between 2 and 5 indicates moderate thickening, and ratio >5 indicates severe thickening.
Mobility of the valve
The mobility of leaflets is assessed in both parasternal long axis (PLAX) and apical four-chamber views. The extent of doming of anterior leaflet can be assessed objectively by Reid grading system. A line is drawn from the junction of the posterior wall of aortic root and anterior mitral leaflet to the tip of the mitral leaflet (xy-H). A perpendicular line is drawn to the leading edge of the maximum dome (ab-L). Mobility is expressed as a slope by dividing the height of the dome by the length of the dome – H/L [Figure 2]b and [Table 3].
Rheumatic process although affects the whole mitral apparatus, it is the subvalvar pathology that carries a significant impact on the outcome of BMV. Chordae undergo thickening, fusion, shortening, and calcification. 2D echo assessment of subvalvar structures is essential. Usually, visual assessment is sufficient to make a decision regarding management. However, objective assessment can be done using Iung et al. score [Table 4]. The chordal length is measured in four-chamber or two-chamber view. Mild subvalvar disease is indicated by chordal length more than 10 mm. Severe subvalvar disease is diagnosed by thickened chordae measuring <10 mm [Figure 3]. Calcification of valve of any extent by fluoroscopy carries high risk of MR following BMV. Wilkins score also helps assess subvalvar pathology-vide table. Modified long axis and four-chamber views are used to properly visualize the chordae and their abnormalities.
Calcification is identified by bright echogenic spots over the leaflets. The presence of calcium over commissures is an absolute contraindication for BMV; however, some experienced operators do perform BMV when only one commissure is calcified. Calcium restricted to the body of the leaflets is not a contraindication for BMV.
| Step 2: Severity of Mitral Stenosis|| |
MS is graded as mild, moderate, and severe depending on valve area, mean gradient across mitral valve and tricuspid regurgitation (TR) peak gradient [Table 5] as per the guidelines laid down by the European Association of Echocardiography and American Society of Echocardiography (ASE). There are other parameters to assess the severity of MS such as mitral leaflet separation and valve area estimation by Doppler pressure half time and continuity equation.
|Table 5: European association of echocardiography/American society of echocardiography classification of severity of mitral stenosis*|
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Assessment by planimetry
Mitral valve area (MVA) measured by planimetry in short-axis view of mitral valve correlates best with explanted valves and is the reference standard. This measurement is not affected by flow conditions, compliance of LA, and presence of associated valve lesions.
Smallest orifice is the maximum opening in mid-diastole at the tips of mitral leaflets. This is identified while scanning from LA to left ventricular (LV) apex and frozen for planimetry in short axis of mitral valve [Figure 4].
Gray-scale gain should be lowered since increased gain leads to blooming of echoes and underestimates the area. Inner contour of mitral orifice is planimetered and commissures are to be included if open. Three measurements on an average are taken when the patient has sinus rhythm and five to ten measurements while the patient has atrial fibrillation. Calcification makes the tracing difficult.
Mitral leaflet separation index
It is measured in PLAX view and apical four-chamber view. The distance between the tips of both leaflets when widely separated in diastole is measured for at least three cardiac cycles, and then, the average is taken. An index of 0.8 cm or less predicts severe MS. 1.1–1.2 or more indicates mild MS.
Continuous wave Doppler and color-guided parallel alignment of Doppler beam in apical four-chamber view are necessary to achieve maximum velocity across mitral valve. Pulse wave Doppler or high pulse repetition frequency can be of value and give better spectral Doppler waveform because of better signal to noise ratio.
Maximum and mean gradients are calculated by tracing the diastolic flow waveform. Mean gradient is hemodynamically more relevant than peak gradient because maximal gradient depends on LA compliance, LV diastolic function, and associated MR. Mean gradient more than 10 mmHg indicates severe MS [Figure 5]a.
|Figure 5: (a) Measuring peak, mean gradients, and pressure half time. Mean gradient measures 14 mmHg and P1/2t of 264 ms suggesting severe mitral stenosis. (b) In this spectral Doppler waveform, only gradients can be measured. P1/2 t cannot be measured|
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Pressure half time
Pressure half time (P1/2t) is the time interval between the maximum mitral gradient in early diastole and the time point where the gradient becomes half of the peak initial value, expressed in milliseconds.
Valve area is inversely related to the decline of the velocity of diastolic transmitral blood flow. MVA is derived using an empirical formula: MVA = 220/P1/2t cm2. P1/2t is derived by tracing the slope of deceleration of E wave on Doppler spectral display of transmitral flow, and the valve area is calculated automatically by the software [Figure 5]a.
When the contour of deceleration slope has two slopes, usually the slope in mid-diastole is traced to derive the P1/2t. In atrial fibrillation, slope of longer diastole and an average of five cycles should be taken. Sometimes, mid diastolic flow is higher than early diastole, then P1/2 t method cannot be used to assess MS [Figure 5]b.
P1/2t depends mainly on mitral valve orifice. However, diastolic compliance of LA and LV, initial gradient across mitral valve, and contractile force of LA also contribute to P1/2t.
P1/2t is less dependent on heart rate, and flow across mitral valve and can be used in varying R-R intervals such as atrial fibrillation.
Pitfalls of P1/2 t:
- If significant aortic regurgitation (AR) coexists, increase in LV end-diastolic pressure decreases the late diastolic gradient between LA and LV, leading to decrease in P1/2t thus overestimating MVA
- If atrial septal defect (ASD) coexists, left to right shunt decompresses LA and decreases gradient between LA and LV, leading to decrease in P 1/2t, thus overestimating MVA
- If LV relaxation is abnormal, for example, LV hypertrophy, then deceleration time and P1/2t are both prolonged, leading to underestimation of MVA.
When transmitral flow does not have homogeneous deceleration, the initial part of the slope can be ignored ( first 300 ms) and P1/2t can be obtained from the slope in mid-diastole.
Mitral valve area by continuity equation
Continuity equation is based on the law of conservation of mass and assumes that volume of blood flow through the mitral annulus should be equal to flow across the mitral orifice. LV outflow tract (LVOT) can be substituted for mitral annulus. This substitution is valid only if there is no significant AR [Figure 6].
|Figure 6: Mitral valve area by continuity equation (a) parasternal long-axis view to measure the left ventricular outflow tract diameter (b) A4C view to measure mitral stenosis velocity time integral (c) A5C view to measure left ventricular outflow tract velocity time integral. Left ventricular outflow tract diameter = 1.96 cm, left ventricular outflow tract velocity time integral = 17.4 cm, mitral stenosis velocity time integral = 74.9 cm, mitral valve area = 1.96 × 1.96 × 0.785 × 17.4/74.9 = 0.7 cm2|
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Flow across LVOT = LVOT area (LVOT diameter2 × 0.785) × LVOT velocity time integral (VTI).
Then MVA = LVOT flow/MS VTI.
| Step 3: Size of Left Atrium and Spontaneous Echo Contrast|| |
LA size should be assessed in PLAX view. The widest dimension anteroposteriorly is measured. Although the American Society of Echocardiography does not recommend this dimension as a standard measure of LA, it is an important parameter for BMV. LA size <5 cm predicts better procedural success of BMV. Aneurysmally dilated LA (>6 cm), however, predicts unfavorable results after BMV and procedural failure.
Spontaneous echo contrast (SEC) may be present within LA. Objective assessment of SEC is available and may be used. LA should be carefully examined along its free wall, roof, near appendage, and near pulmonary veins for the presence of thrombus [Figure 7]a-e].
|Figure 7: (a) Ball valve thrombus (Type V). (b) Transesophageal echocardiography mid esophageal 90° 2 chamber view – pectinate muscle in the left atrial appendage. (c) Transesophageal echocardiography mid esophageal 60° short-axis view showing clear left atrial appendage. (d) Transesophageal echocardiography mid esophageal 60° short-axis view showing spontaneous echo contrast in the left atrial appendage. (e) Transesophageal echocardiography mid esophageal 60° short-axis view showing Type IIb thrombus in the left atrial appendage|
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LA appendage should be carefully visualized in parasternal short-axis view and apical two-chamber view. Size of the appendage and presence of thrombus should be assessed. LA appendage (LAA) thrombus confined within the appendage not protruding into LA is usually not considered a contraindication for BMV.
LA thrombus is classified by Prabhavathi into five types [Table 6].
|Table 6: Manjunath classification of the left atrial and left atrial appendage thrombus|
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Experienced operators perform BMV when there is Ia; Ib and IIa thrombus in LA, using over the wire modification of the procedure. IIb, III to V are absolute contraindications for BMV.
| Step 4: Interatrial Septum|| |
Interatrial septum should be carefully assessed for the presence of patent foramen ovale or ASD (Lutembacher's syndrome). Interatrial septal aneurysm or bulging septum toward the right atrium should be noted and reported because this feature may give rise to difficulty in septal puncture. The presence of thrombus over interatrial septum is a contraindication to BMV.
| Step 5: Mitral Regurgitation|| |
The presence and severity of MR should be assessed by color Doppler echocardiography and Doppler interrogation. Semi-quantitative estimation is made by the ratio of MR jet area and LA area. Dense spectral Doppler signals indicate at least moderate MR. Patients can undergo BMV if the MR is less than Grade II and MR with central jets [Figure 8]a and [Figure 8]b without significant calcification of the valve. However, BMV is a relative contraindication in patients with heavily calcified valve with more than Grade II MR or MR with eccentric jets [Figure 9]. Corroborative evidence of significant MR is suggested by enlarged LV. MR echocardiographic score by Padial et al. is useful to predict significant regurgitation after BMV with high sensitivity and specificity. Three characteristics predict significant MR after BMV. They are uneven mitral leaflet thickening, severe subvalvar disease, and commissural calcification. However, the occurrence of MR after BMV is highly unpredictable. Already existing MR with central jet may sometimes decrease after BMV because of altered coaptation points.
|Figure 8: (a and b) Mild mitral regurgitation, central jet – not a contraindication for balloon mitral valvotomy|
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|Figure 9: Eccentric moderate mitral regurgitation – balloon mitral valvotomy may result in severe mitral regurgitation|
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| Step 6: Assessment of Pulmonary Hypertension|| |
Pulmonary arterial hypertension ensues whenever the pulmonary venous pressure raises due to increased LA pressure. The severity of pulmonary hypertension should be assessed. Right ventricular (RV) systolic pressure is estimated by Bernoulli equation using TR peak gradient [Figure 10]. There is no correlation between the severity of TR and RV systolic pressure. Organic tricuspid valve disease may coexist with MS, and if significant tricuspid stenosis (TS) is noted, that can also be managed by balloon valvotomy. However, if more than moderate TR is present along with TS then surgical management is indicated. Tricuspid annulus diameter more than 4 cm is an indication for tricuspid annuloplasty. Commonly right atrium and right ventricle enlarge depending on the severity of pulmonary hypertension, and paradoxic septal motion may be seen. In case of poor TR signal, then pulmonary artery mean and diastolic pressures can be estimated using pulmonary regurgitation Doppler signal.
|Figure 10: Tricuspid regurgitation peak gradient measures 77 mmHg suggesting severe pulmonary artery hypertension|
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In recent times, 2D echo and Doppler echo have taken over M-mode echocardiography in the diagnosis and assessment of severity of MS. Some of the M-mode features used are given below.
Diastolic excursion (DE) amplitude and EF slope can indicate pliability and severity of MS, respectively. DE amplitude more than 18 mm indicates pliable anterior leaflet. EF slope is decreased proportionately to the severity of MS. Usually, EF slope 10–20 mm/s indicates severe MS. In the presence of MR without significant MS, M-mode feature of the anterior motion of posterior leaflet indicates restricted mobility and suggests rheumatic etiology.
Wilkins et al. proposed a scoring system to predict the outcome after BMV. The four important mitral valve characteristics, namely, leaflet mobility, valve thickening, subvalvar thickening, and calcification are given a score of 1–4 depending on their severity.
Total echocardiographic score is 16. A score of <9 gives optimal results after BMV; score >11 gives suboptimal results after BMV.
Mitral regurgitation echocardiographic score
Uneven mitral leaflet thickening, severe and extensive subvalvular deformation, and commissural calcification are the three characteristic anatomic features associated with the development of significant MR after BMV.
The combination of Wilkins score and Padial MR echocardiographic score predicts the success of BMV and occurrence of significant MR.
| Step 7: Assessment of Other Valves|| |
Commonly aortic valve pathology coexists with rheumatic mitral valve disease. The presence and severity of aortic stenosis and regurgitation should be carefully assessed by 2D and Doppler examination. Mild degrees of aortic stenosis and regurgitation are not contraindications for BMV. Age and sex of the patient should be taken into consideration when aortic valve disease coexists. For example, young female with severe MS, mild-to-moderate AR with or without mild aortic stenosis may undergo BMV safely to relieve her symptoms, so that she may complete her family before she requires another intervention. Rarely, congenital bicuspid aortic valve may coexist with rheumatic mitral valve disease.
The rheumatic process affects tricuspid valve in about 7%–10% of patients, resulting in TS [Figure 11] and/or organic TR. Functional TR is almost always seen in significant MS. The severity of TS is usually assessed by Doppler gradients of TS velocity curve. An empiric constant of 190 is used for tricuspid valve instead of 220 while calculating valve area by pressure half time method.
|Figure 11: Apical 4 chamber view showing doming of both mitral and tricuspid valves|
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Pulmonary valve involvement is extremely rare in rheumatic heart disease.
| Step 8: Ventricular Function|| |
Assessment of LV systolic function is an important part of echocardiographic assessment of valvular heart disease. LV function in MS is usually normal. LV dysfunction may be due to myocarditis, part of active rheumatic process, or primary muscle disease. LV dysfunction may adversely affect the outcome after intervention.
| Step 9: Contraindications for Balloon Mitral Valvotomy|| |
Finally, the contraindications for BMV should be looked for specifically and reported. Features such as LA thrombus, especially in the body or attached to interatrial septum, bicommissural calcification, nonfusion of commissures, severe subvalvar thickening, more than mild MR, significant aortic valve, or tricuspid valve involvement are absolute contraindications for BMV. Associated coronary artery disease which requires coronary artery bypass surgery is another contraindication for BMV. Sequelae of coronary artery disease may be inferred by regional wall motion abnormality.
| Rhythm|| |
Atrial fibrillation is not uncommon in MS. It is more likely related to age and has poor correlation with the size of LA and severity of MS. Doppler assessment of severity of MS in atrial fibrillation requires averaging of at least five beats. Long-diastolic period should be selected to estimate Doppler gradients and pressure half time.
| Transesophageal Echocardiography|| |
Transesophageal echocardiography (TEE) is useful in certain situations, especially before BMV.
- To rule out LA and LAA thrombus
- To assess MR
- To assess interatrial septum.
TEE may be used to aid septal puncture, especially during BMV.
Mid esophageal aortic short-axis view and two-chamber view are used to visualize the LAA. Sometimes, pectinate muscle within appendage is mistaken for thrombus. Usually, pectinate muscle has the same echo texture as LAA wall.
| Three-Dimensional Echocardiography|| |
Real-time transthoracic and transesophageal three-dimensional (3D) echocardiography may be useful in enhancing the objective assessment of mitral valve morphology, especially to visualize the narrowest orifice of mitral valve for planimetry. Subvalvar fusion is better appreciated by 3D echocardiography. 3D estimation of MVA correlates better with catheter-derived values. The advantage of 3D echocardiography is that mitral valve morphology is assessed in its entirety from single-imaging plane. Real-time 3D echo (RT3DE) scoring system for MS objectively assess mitral valve morphology. Each scallop of both leaflets is given a score taking into account, thickness, mobility, and calcification. Subvalvar apparatus is divided into three segments – proximal, middle, and distal third and given score based on thickness and separation. All the score points are summed to calculate total RT3DE score ranging from 0 to 31 points. Score more than 14 indicates severe mitral valve involvement.
| Conclusion|| |
Echocardiography remains an invaluable tool in the assessment of valvular heart disease. In MS, all possible echocardiographic modalities and views [Table 7] are used to evaluate its severity and assess suitability for BMV [Box 1].
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]