6th May 2025

Mitral stenosis

Pathology and Epidemiology

Mitral stenosis (MS) refers to narrowing of the mitral valve orifice. When severe, this leads to elevation of pressures in the left atrium and backwards into the pulmonary circulation. Historically it was more prevalent, typically caused by rheumatic fever as a delayed manifestation of group A streptococcal infection, but its incidence and prevalence is falling in the western world. As a consequence, an increasing proportion of cases are caused by calcific degenerative stenosis, seen in elderly patients. In both cases the mitral valve itself stiffens, leading to narrowing of the mitral orifice. 

Rheumatic disease leads to thickening of the mitral valve leaflet and commissural fusion with notably restricted motion at the leaflet tips. Shortening, calcification and fusion of the mitral chordae is also seen.

In calcific disease calcium deposits build up on the valve itself leading to thickening and calcification at the base of the leaflets impairing motion.

Other less common causes include mitral annular calcification, side effects of radiotherapy and congenital stenosis such as is seen in the Shone complex.

Presentation – Symptoms

Symptoms are typically related to either the presence of atrial fibrillation or elevated pulmonary pressures. In severe disease, significant elevation of pressures within the left atrium leads to atrial dilation which is a potent substrate for atrial fibrillation. This can thus lead to palpitations, dyspnoea and chest discomfort.

Alongside this, elevated pressures in the left atrium can lead to elevated pulmonary pressures. This can lead to exertional dyspnoea, cough, haemoptysis, chest pain due to elevated right ventricular pressures. These symptoms can be worse in the context of atrial fibrillation, as impaired atrial pump function can reduce forwards flow and further increase left atrial and thus pulmonary pressures.

Due to the high risk of atrial fibrillation and stasis within the left atrium they are at a markedly elevated risk of cerebrovascular accident which may be the first presenting feature. 

Significant MS is incredibly poorly tolerated in pregnancy. The haemodynamic changes of pregnancy include significant volume expansion, which becomes an issue when faced with a fixed obstruction between the left atrium and ventricle, typically leading to signs of heart failure in the second trimester which may be its first point of diagnosis.

Presentation – Signs

When severe there are a number of typical signs:

• Cutaneous vasodilation (mitral facies)
• Pulmonary congestion – rales
• Evidence of right sided heart failure – right parasternal heave, elevated jugular venous pressure, ascites, peripheral oedema
• Diastolic murmur heard best at the apex on expiration

Diagnosis and Investigations

As with previous diseases, the above constellation of symptoms and signs should suggest a differential of MS. They will typically undergo the same battery of tests as other potential valve disease cases including ECG, Chest Xray, Echocardiogram and routine blood tests.

ECG may demonstrate atrial fibrillation, P mitrale due to left atrial enlargement if in sinus rhythm and evidence of pulmonary hypertension such as right axis deviation and a tall R wave in V1 and V2.

Chest Xray may show signs of pulmonary congestion but is typically non-specific.

As with other valve disease, echocardiogram is the mainstay of diagnosis. Colour flow doppler will demonstrate turbulent anterograde mitral flow, while 2d views may show an echobright thickened base in calcific disease, while in rheumatic disease the leaflets themselves become thickened and may demonstrate a domed ‘hockey-stick’ type appearance. The left atrium is typically markedly dilated on 2d views and there may be evidence of spontaneous echo contrast within it, suggesting sluggish flow. Spectral doppler will demonstrate elevated trans mitral pressures, while a short axis view of the mitral valve leaflets tips is imperative.

Grading Severity 

Echocardiographic criteria are commonly used for grading MS. MS is classified as clinically significant when the mitral valve area is <1.5cm2. This encompasses moderate and severe MS. 

Other features suggestive of significant stenosis include a mean pressure gradient of >10mmHg, diastolic pressure half time of <220ms and systolic pulmonary artery pressure of >50mmHg.

Criteria for interventional treatment 

Intervention is typically reserved for symptomatic patients with moderate-severe rheumatic MS. Intervention can be considered in asymptomatic patients with either high thromboembolic risk (defined as previous systemic embolism, dense spontaneous echo contrast in the left atrium or new atrial fibrillation) or high risk of haemodynamic compensation (defined as systolic pulmonary artery pressure of >50mmHg at rest, need for a major non cardiac surgery or desire for pregnancy).

For those with degenerative disease, evaluation of severity is difficulty and many of the above parameters lack validation in this cohort. Mean transmitral gradient has been shown to have prognostic value but a holistic assessment of the patient is required.

Treatment options

Percutaneous mitral commissurotomy is typically first line in symptomatic rheumatic valve patients with favourable characteristics. Unfavourable characteristics which would preclude PMC include old age, previous commissurotomy, NYHA class IV, permanent AF, severe pulmonary hypertension, very small valve area, more than mild MR or a left atrial thrombus. Where alternative surgery is to be performed (such as in CABG or if concomitant valve disease requiring intervention) then surgery is likely to be preferred to PMC.

Mitral valve replacement surgery can be performed for symptomatic patients who are not suitable for PMC due to the above unfavourable characteristics.

Intervention in degenerative MS is performed less commonly. Degenerative MS is not amenable to transcatheter intervention and surgery is both challenging and without good outcome data.

Medical therapy typically includes anticoagulation in all patients with significant mitral stenosis with atrial fibrillation, irrespective of CHADS-VaSC score. These patients will require vitamin K antagonists not DOACs which have been shown to be less effective. Aside from this, diuretics and rate control medications (such as beta blockers, calcium channel blockers and ivabradine) can help with symptom control. The former helps to offload the heart, while the latter slows the heart rate, allowing for a longer time in diastole for blood to move through the stenotic valve, both ultimately aiming to help improve dyspnoea.