Mitral stenosis
Etiology
Rheumatic fever and its sterile complications are almost a unique cause of MS. Even though the prevalence of rheumatic fever is declining in western countries, it is still the most common cause of MS worldwide.
Other etiologies represent a very small percentage of clinically significant MS.
Other aetiologies of MS:
- post-inflammatory processes – Systemic Lupus Erythematosus or Rheumatoid Arthritis
- annular calcification
- radiation induced valve disease
- mechanical obstruction – tumour, thrombus, vegetation
- degenerative and congenital MS
Pathophysiology
Stenosis develops typically decade/s after the episode of acute rheumatic carditis. Firstly, multiple inflammatory foci (Aschoff bodies) form in the endocardium and myocardium. Small vegetations along the border of the valves may also be observed.
After years, mostly due to abnormal flow dynamics, the valve damage progresses into commissural fusion with typically thickened rolled free edges, which is the main finding of rheumatic valve disease, but anatomical lesions may combine to varying degrees
- fusion of one or both commissures
- thickening, fibrosis and calcification of the valve
- chordal thickening
- restricted leaflet motion
- fusion of the subvalvular apparatus
This obstruction limits cardiac output and increases pressure in the LA, which, in turn, raises pulmonary circulation pressure (pulmonary oedema at mean capillary pressure >25 mmHg).
Normal mitral valve area is 4-6 cm2.
A diastolic transvalvular gradient between LA and LV appears if the area is <2cm2. Patients start to experience valve-related symptoms - exertional dyspnea during exercise or tachycardia.
Severe mitral stenosis occurs with a valve area of less than 1 cm2. The rising pressure in LA has many hemodynamic consequences summed up below (Image 1):
Moore RA, Flores S, Cooper DS. Critical care of patients with paediatric valvar cardiac disease. Cardiol Young. 2014 Dec;24(6):1071-6.
Consequences
- Left atrial dilatation and rheumatic insult of atria increases the risk for atrial fibrillation and subsequent thromboembolism.
- Pulmonary hypertension - initially reversible morphological changes > reactive pulmonary vasoconstriction or reduced lung compliance
- Right ventricular dilatation and tricuspid regurgitation – result of increasing pulmonary arterial pressure
- LV contractility is usually preserved, but 1/3 of chronic MS patients has decreased LV EF
Symptoms
Patients with known mitral stenosis may be asymptomatic or have mild symptoms for decade/s.
Most of the symptoms are a result of the congestion before the mitral valve and usually worsen with exercise or increased heart rate. Mitral stenosis symptoms may first appear in pregnancy, with infection or when patients develop AF.
- Shortness of breath, exertional dyspnoea
- Chest discomfort or pain
- Fatigue, dizziness or syncope
- Swollen feet or legs
- Palpitations, irregular rhythm - AF
Echocardiography of MS
Echocardiography is the most specific and sensitive method of diagnosing and quantifying the severity of mitral stenosis.
What is assessed?
- anatomic abnormalities of MV – mobility, thickening, motion, calcification, separation
- trans-valvular gradients and area of the MV
- involvement of the subvalvular apparatus – chordae, musculi papillares
- LA size and pressure
- pulmonary pressures
The two most important factors to determine severity of MS are mitral valve area (MVA) and mean MV gradient (MG).
Assessing the anatomy of MV
It is important to describe what anatomical changes affect MV. Both parasternal and apical windows are used, but the degree of leaflet restriction is best appreciated in PSAX and PLAX views.
You can see the degree and distribution of thickening, calcification and commissural fusion, along with the appearance and mobility of the leaflets. The subvalvular apparatus is best evaluated in apical views.
The following is a list of features characteristic for rheumatic mitral stenosis:
- Leaflet thickening and fibrosis is confined predominantly to the tips and commissures (MV degenerative calcification tends to spare the leaflet tips!), calcification comes after thickening.
- Chordal thickening, fusion and shortening
- “Hockey stick” or “elbowing” appearance of the MV – leaflet base has more mobility than the restricted and fused leaflet tips, the anterior leaflet then appears to ‘dome’ = bulges towards the LV as blood is caught in the leaflet. This also causes the opening snap heard during auscultation.
- Commissural fusion in the PSAX at the level of MV
The assessment of valve morphology is increasingly important for the selection of candidates for percutaneous mitral commissurotomy (PMC). Scores have been developed that take into account valve thickening, mobility, calcification, subvalvular deformity and, more recently, commissural areas (Image 2+3).
Camm AJ, Luscher TF, Serruys PW. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press, found on page 639
Baumgartner, Helmut, et al. "Echocardiographic assessment of valve stenosis: EAE/ASE recommendations for clinical practice." Journal of the American Society of Echocardiography 22.1 (2009): 1-23.
Video 1 Mitral stenosis, PLAX view - degenerative changes and calcification of both MV cusps, restricted movement of the leaflets centrally.
Video 2 Mitral stenosis, PLAX view - rheumatic changes of the MV - leaflet thickening (4mm), doming of the anterior leaflet, restricted movement of the posterior leaflet = Hockey stick appearace of the anterior leaflet.
Video 3 Mitral stenosis, PSAX view at the level of the valve - anterior and posterior leaflet and both commissures are visualized. Overall anatomy of the MV and planimetry of the stenotic orifice may be assessed in this view. Observe the rheumatic changes of the MV - leaflet thickening, anterolateral commissural fusion and reduced MV area (2D planimetry - 1-1,5 cm2)
Video 4 Mitral Stenosis, A4C view - note the significantly enlarged LA (LAVi 53.6 ml/m2)
Video 5 Mitral stenosis, A4C view with colour Doppler (increased flow velocities apparent in colour Doppler)
Video 6 Mitral stenosis, A4C view - heavily degenerated and calcified MV, the LA is also significantly dilated (LAVi 55.6 cm3/m2)
Grading severity of MS
Mitral valve stenosis severity is described by the mitral valve area (MVA) and the mean MV gradient (MG).
Both of these factors are heavily influenced by loading conditions and coexistent valvular disease. Heart rate and rhythm should always be reported. If the patient is in AF, estimation of MVA and MG should not be measured in extremes of HR and R-R interval.
Measurements should be averaged from five beats or made on matching R-R interval beats.
Image 4 Grading of MS severity
1) Trans-mitral pressure gradient
Leaflet restriction causes reduced MV opening and prevents complete LA diastolic emptying, which leads to volume and pressure overload of LA. When loading conditions are normal, the LA-LV pressure difference is proportional to the degree of valvular stenosis and can be considered a good indicator of MS severity.
How to measure transvalvular gradient ?
Continuous wave Doppler (CW) is used to measure transvalvular velocities that are derived to gradients, using the Bernoulli equation.
The Doppler line needs to be aligned parallel to mitral valve inflow, usually from the apical four chamber view, and go through the vena contracta (the narrowest part of the jet) (more in MR assessment).
First use Colour Doppler for better guidance of the sample line.
Maximal velocity is measured at the peak of E-wave (in sinus rhythm) and corresponds to the maximal gradient. This velocity is highly variable and does not represent the severity of MS.
The mean gradient is calculated from mean velocity of the tracing, it is easy to obtain and reproduce. The gradient can be measured by tracing the dense outline of mitral diastolic inflow and the mean pressure gradient is automatically calculated.
The mean gradient is more relevant, but is significantly dependent on heart rate and stroke volume. This makes it a bad parameter of MS severity where cardiac diseases coexist.
- Presence of aortic regurgitation or LV diastolic dysfunction reduces the LA-LV pressure difference, resulting in a reduction of the mean gradient and underestimating the MS severity.
- Opposite to that, coexistent mitral regurgitation increases LA pressure and therefore the LA-LV pressure difference as well, resulting in higher mean pressure gradient (overestimation of MS severity).
Image 5 CW Doppler measurement of transvalvular velocities in A4C view - the dense outline of mitral diastolic inflow is traced and pressure gradients calculated.
Image 6 CW Doppler measurement of transvalvular velocities, A4C view
2) Mitral Valve Area
Mitral valve area is an important measurement for the estimation of MS severity.
It can be measured directly (direct planimetry) or indirectly in 3 ways using transvalvular Doppler profiles – pressure half-time, PISA method and continuity equation.
a) Planimetry
Planimetry of mitral valve area is the most reliable method for grading the MS severity as it is not as influenced by loading conditions.
It is usually performed in a zoomed PSAX view at the level of the leaflet tips where the orifice is seen smallest.
When the leaflet tips are seen, you need to trace the stenotic orifice in a frozen frame where the valve is at a point of maximal opening, usually during early diastolic filling. The shape of the orifice may vary greatly and it is sometimes difficult to acquire a good image quality. Colour Doppler is a helpful tool to visualise the geometry and position of the orifice, but tracing the CFD contour is not recommended.
It may be impossible to perform this method in patients with heavily calcified valves, poor image quality in parasternal windows or when the plane alignment is inappropriate. Optimization of image gain, depth and compression to avoid flaring of the leaflet tips lessens the risk of under or overestimating the MVA.
Image 7 Planimetry of the Mitral Valve Area (MVA) in PSAX view - the stenotic orifice is traced in a frozen frame.
b) Pressure half-time (P½t, PHT)
Pressure half-time method is based on the assumption that the rate at which the gradient drops during diastole corresponds to the severity of mitral stenosis.
The bigger the orifice is, the faster will the LV fill and the more quickly the gradient will drop. In MS, the time it takes for early trans-mitral velocity to fall by half is prolonged and we can see a shallower deceleration of the MV E wave.
MVA is then calculated by dividing a LV relaxation constant value of 220 by the P½t.
How to measure PHT?
Acquire an apical four chamber view of the MV and use the CW Doppler. Measure the slope from the maximal inflow velocity at early diastolic filling, align the calipers to the curve and the scanner will automatically derive the pressure half-time.
The estimation of the MVA should be averaged in 3 consecutive beats. If the patient is in AF, you should use an average value from 5 beats.
Image 8 CW Doppler Pressure half-time (PHT) measurement, A4C view
- place the cursor through the centre of the orifice and enter CW mode.
- Ensure that the line is parallel with the trans-mitral flow
- Adjust the velocity scale to maximise the Doppler signal size
- Measure the deceleration slope from the peak (highest velocity) to the baseline of 0 cm/s
Image 9 CW Doppler measurement of PHT - Bi-modal E signal
PHT technique may be hampered and unreliable in:
a) Diastolic dysfunction (over estimation of MS severity)
b) Aortic regurgitation (under estimation of MS severity)
c) After valvuloplasty (unreliable)
d) Heavily calcified valves (unreliable)
c) PISA radius
This method is usually more time consuming and limited by the inability to measure the angle of MV leaflets on some machines, but may be a good alternative when other Doppler methods are inaccurate.
The PISA method assumes the flow convergence is hemispherical, but in rheumatic disease the atrial surface of MV is usually funnel shaped/conical and a correction factor must be used to eliminate overestimation. This factor is measured as an angle on the atrial surface of the leaflets in the diastole. Then multiplying the flow rate by the angle of the atrial surface of the leaflets divided by 180 corrects for the non-planar geometry and provides a more accurate estimate of MVA.
d) Continuity equation
Continuity equation assumes that all blood flowing through the MV also must flow through the LVOT. MVA is calculated as LVOT stroke volume (SV) divided by MV VTI.
This method cannot be used in the presence of mitral regurgitation and/or aortic regurgitation because of great over/underestimation of the MS severity. In patients with AF, SV varies significantly from beat-to-beat and needs to be measured in similar R-R intervals.
Other supportive parameters of severe mitral stenosis
3) LA volume
The presence of MS causes chronic pressure overload of the LA. This usually results in remodelling and dilatation of the LA.
The LA volume is best estimated using the Simpson’s biplane method – trace the whole LA endocardium in two orthogonal views, usually in apical 4 chamber and apical 2 chamber views at ventricular end systole (maximum LA size).
4) Pulmonary artery pressure
The increased LA pressure translates to increased pulmonary artery capillary wedge pressure and therefore systolic pulmonary artery pressure (PAP).
Alongside with the mean trans-valvular gradient, the PAP reflects the consequences of MS and has a prognostic value.
Estimation of PAP on TTE is important in severe MS for the appropriate timing of intervention.
Intervention
The timing and type of intervention should be decided on the basis of clinical appearance, mitral valve anatomy and local expertise.
Symptomatic patients with clinically significant mitral stenosis are candidates for either mitral valve replacement or balloon valvuloplasty.
Below is an algorithm for management of clinically significant mitral stenosis (Image 10):
Vahanian A, Beyersdorf F, Praz F, et al. ESC/EACTS Scientific Document Group. 2021 ESC/EACTS Guidelines for the management of valvular heart disease. Eur Heart J. 2021 Aug 28:ehab395. doi: 10.1093/eurheartj/ehab395. Epub ahead of print. PMID: 34453165.
1) Percutaneous mitral commissurotomy (PMC)
Percutaneous mitral commissurotomy (PMC), also known as percutaneous mitral balloon valvotomy, is the first-line therapy for managing rheumatic mitral stenosis in patients who have suitable mitral valve morphology on echocardiography – thickening confined to the tips, little chordal involvement, good mobility of anterior leaflet and no commissural calcification.
The Wilkins score assesses morphological criteria and determines the patient’s suitability for PMC - a score of 8 or less predicts a more favorable outcome than those with a higher score. However, a score higher than 8 does not exclude a patient from having a mitral valvuloplasty (Image 11).
European Heart Journal, Volume 38, Issue 36, 21 September 2017, Pages 2739–2791, https://doi.org/10.1093/eurheartj/ehx391
TOE is performed before the procedure to exclude LA thrombus as that is the most important contraindication to PMC. The PMC is performed via a femoral vein and transseptal catheterization with a unique balloon tip catheter (Image 12), which is then expanded with fluid. Pressure is applied to the mitral valve, resulting in separation along the plane of least resistance, which are the commissures.
The valve area usually increases over a 100% (>2cm2) in more than 80% of patients, the valve function improves and pulmonary pressures decrease, both at rest and during exercise.
https://www.mayoclinic.org/-/media/kcms/gbs/patient-consumer/images/2016/12/21/15/57/mcdc7_valvuloplasty-8col.jpg
The long-term outcome after PMC is mainly determined by the immediate procedural results. Failure rates range between 1% - 15% and severe mitral regurgitation is the most common immediate complication.
When the results are unsatisfactory, surgery is required in the following months.
Long-term results after successful PMC are good.
The table below sums up indications for PMC (Image 13):
Vahanian A, Beyersdorf F, Praz F, et al. ESC/EACTS Scientific Document Group. 2021 ESC/EACTS Guidelines for the management of valvular heart disease. Eur Heart J. 2021 Aug 28:ehab395. doi: 10.1093/eurheartj/ehab395. Epub ahead of print. PMID: 34453165.
Image 14 Contraindications of PMC
Vahanian A, Beyersdorf F, Praz F, et al. ESC/EACTS Scientific Document Group. 2021 ESC/EACTS Guidelines for the management of valvular heart disease. Eur Heart J. 2021 Aug 28:ehab395. doi: 10.1093/eurheartj/ehab395. Epub ahead of print. PMID: 34453165.
2) Surgery
If the PMC is not suitable, a surgical approach is the only alternative. An open-heart mitral commissurotomy may be considered, where the surgeon may not only correct commissural fusion, but also chordal and papillary fusion. Complete valve replacement is another option, mechanical valves are used for their durability at the expense of life-long anticoagulation and operative mortality of 3-10%.
3) Medical therapy
- symptomatic therapy – diuretics, beta-blockers, digoxin or verapamil/diltiazem
- anticoagulation – patients with new-onset or paroxysmal AF. In patients in sinus rhythm oral anticoagulation is indicated when there has been a history of embolism/thrombus in the LA. If the MS is severe, patients should not use NOACs and be kept on vitamin K antagonists.
- Cardioversion before procedure is not indicated as it does not durably restore sinus rhythm!
References
- CAMM, A. J., LÜSCHER, T. F., & SERRUYS, P. W. (2009). The ESC textbook of cardiovascular medicine. Oxford, Oxford University Press
- Understanding the role of echocardiography in the assessment of mitral valve disease. European Society of Cardiology [online]. Copyright © 2021 European Society of Cardiology. All rights reserved. [cit. 13.07.2021]. Accessible at: https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-16/Understanding-the-role-of-echocardiography-in-the-assessment-of-mitral-valve-disease
- Alec Vahanian, Friedhelm Beyersdorf, Fabien Praz, Milan Milojevic, Stephan Baldus, Johann Bauersachs, Davide Capodanno, Lenard Conradi, Michele De Bonis, Ruggero De Paulis, Victoria Delgado, Nick Freemantle, Martine Gilard, Kristina H Haugaa, Anders Jeppsson, Peter Jüni, Luc Pierard, Bernard D Prendergast, J Rafael Sádaba, Christophe Tribouilloy, Wojtek Wojakowski, ESC/EACTS Scientific Document Group, 2021 ESC/EACTS Guidelines for the management of valvular heart disease: Developed by the Task Force for the management of valvular heart disease of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS), European Heart Journal, 2021;, ehab395, https://doi.org/10.1093/eurheartj/ehab395
- Mitral Stenosis Workup: Laboratory Studies, Imaging Studies, Other Tests. Diseases & Conditions - Medscape Reference [online]. Dostupné z: https://emedicine.medscape.com/article/155724-workup#c5
- Omran AS, Arifi AA, Mohamed AA. Echocardiography in mitral stenosis. J Saudi Heart Assoc. 2011;23(1):51-58. doi:10.1016/j.jsha.2010.07.007
- 11.5 Quantification of Mitral Stenosis Severity | 123 Sonography. Online Echocardiography Course & Sonography Training | 123 Sonography [online]. Dostupné z: https://www.123sonography.com/ebook/quantification-mitral-stenosis-severity
- Nunes MCP, Nascimento BR, Lodi-Junqueira L, et al Update on percutaneous mitral commissurotomy Heart 2016;102:500-507.
