6th May 2025

Mitral Regurgitation

Pathology and Epidemiology

The mitral valve separates the morphological left atrium and ventricle and is composed of a narrow based but elongated anterior valve, and a broad based but shallow posterior valve. These are separated into three morphological regions termed scallops, delineated by two swallow indentations on the posterior leaflet. The subvalvular apparatus is comprised of the chordae which typically secure the valve leaflets to the anterolateral and posteromedial papillary muscles.

The mitral valve annulus is saddle shaped and comprised of a fibrous anterior portion in continuity with the aortic valve, while the posterior section is more loosely attached to adjacent tissue and is more mobile during the cardiac cycle.

Mitral regurgitation (MR) refers to retrograde flow of blood through the mitral valve during systole and can occur in the context of disease of any of the above components. As described earlier, primary valve disease occurs due to failure of either the valve leaflets or subvalvular apparatus, while secondary regurgitation is regurgitation through competent valve leaflets due to dilation or abnormalities of the annulus.

Trace or mild regurgitation is a common finding even in healthy hearts, and MR is the second most common valve disease after AS. 

Primary causes include infective endocarditis leading to valve perforation, degenerative or myxomatous valve disease, papillary muscle dysfunction or chordal rupture in the context of myocardial ischaemia.

Secondary causes include dilation of the left ventricle of any cause (such as a cardiomyopathy) and dilation of the left atrium of any cause (such as restrictive cardiomyopathies).

The distinction may seem arbitrary as it leads to the same process, but this difference is important as ultimately the treatment options for the two categories are markedly different.

Presentation – Symptoms

As with AR, the nature of the presentation depends on the acuity of the disease. In acute regurgitation there is little time for the heart to adapt to significant volume loading of the left ventricle which leads to increased diastolic filling pressures, wall stress and pulmonary congestion, and can lead to haemodynamic collapse. This can manifest as cardiogenic shock, with hypotension, diaphoresis, dyspnoea, reduced GCS, orthopnoea and peripheral oedema.  

 In chronic regurgitation, increased volume loading can be adapted for by dilation of both the left atrium and ventricle to accommodate an increased blood volume, and it is often only when these compensatory mechanisms have reached their limit that patients decompensate and present with typical symptoms of heart failure.

Presentation – Signs

Signs typical of severe MR include:

• Pansystolic murmur loudest in the apical region radiating to the axilla
• Displacement of the apex laterally due to LV dilation
• Crackles on auscultation of the lung if pulmonary congestion present
• If mitral valve prolapse is the cause, then a mid-systolic click can be heard

Signs typical of acute severe regurgitation are those of acute heart failure and cardiogenic shock, including:

• Hypotension
• Hypoxia
• Tachycardia
• Pulmonary congestion
• Reduced urine output
• Impaired cognitive function

Diagnosis / Investigations

Diagnosis should be considered in the context of the above findings. Patients will typically receive a chest Xray, ECG and TTE alongside blood tests which will normally include full blood count, urea and electrolytes and NT pro BNP levels.

Chest Xray can demonstrate a dilated cardiac shadow if chronic, while if symptomatic will often show pulmonary congestion with or without pleural effusions. ECG can show evidence of left atrial enlargement, P Mitrale, which manifests as a broad bifid P wave, otherwise may not show any specific signs for regurgitation.

TTE is the most useful test to make the diagnosis and severity criteria will be discussed below. Colour flow doppler can demonstrate the presence of MR visually, while a combination of spectral doppler and 2D measurements are used to grade severity. As with AR, transoesophageal echocardiography can be considered to better understand the underlying pathology and to help plan for intervention if required.

As with any cause of heart failure and increased wall stresses, NT Pro BNP levels will typically be elevated.

Once significant regurgitation is diagnosed, if a specific underlying cause is being considered then there may be additional tests directed at elucidating this; blood cultures will be relevant for those with infective endocarditis, while angiography may be necessary if ischaemia is the likely cause.

Grading Severity 

Echocardiography is the standard modality for assessment of severity. A number of parameters are typically used to adjudicate severity which are beyond what is required of you at MRCP, but regurgitation is likely severe if regurgitant volume is >60ml, regurgitant fraction is >50%, pulmonary vein flow is reversed in systole and the regurgitant jet takes up >50% of the left atrium on colour flow doppler.

Criteria for treatment 

Patients with severe symptomatic regurgitation typically need surgical intervention. For those with severe asymptomatic regurgitation, surgical intervention is typically recommended when the following criteria are met:

• LVEF <60% or LV end systolic diameter ≥40mm
• AF or pulmonary hypertension (systolic pulmonary artery pressure >50mmHg) secondary to the MR

Treatment options

The vast majority of patients with less than severe MR will need no specific treatment. 

In severe disease, medical therapy typically comprises of diuretics, and in acute disease nitrates can also be used if blood pressure is sufficient, in order to reduce filling pressures. In acute regurgitation with haemodynamic instability then inotropic agents and intra-aortic balloon pumps can also be considered to reduce afterload and improve preload thus increasing cardiac output.

For those patients who meet the above criteria for surgical intervention, repair of the mitral valve is normally preferred, but if not technically feasible then the valve can be replaced. Anticoagulation after repair is sometimes prescribed, though there is limited evidence for this.

As with aortic disease, both bioprosthetic and mechanical mitral valves are feasible. Regarding anticoagulation with vitamin K antagonists, due to lower velocity flow between the left atrium and ventricle, a higher INR is typically required in mechanical mitral prostheses and will typically be indicated in the surgical notes. 

For patients who are failing medical therapy and are not suitable for cardiac surgery then transcatheter options are now available, known as trans-catheter edge to edge repair or TEER. Their role is controversial however, with limited evidence of prognostic benefit and currently they are used largely with palliative intent.