Mitral regurgitation

Overview

Incompetent mitral valve allowing blood to flow back from the left ventricle into the left atrium during systole - one of the most common valvular heart diseases.

Causes

•Leaflet abnormality - mitral valve prolapse (most common in developed world), rheumatic heart disease, infective endocarditis

•Connective tissue disorders - Marfan syndrome, Ehlers-Danlos syndrome (valvular incompetence due to connective tissue pathology)

•Papillary muscle rupture - acute MR 2-7 days post-MI; presents with acute pulmonary oedema/cardiogenic shock

•Annular dilatation - secondary to LV dilatation (e.g. dilated cardiomyopathy)

Presentation

•Pansystolic, high-pitched 'blowing' murmur - loudest at the apex, radiates to the left axilla

•Louder on expiration and with patient rolled to the left lateral decubitus position

•Quiet/absent S1 - incomplete leaflet apposition

•S3 - rapid high-volume LV filling; sign of significant volume overload

•Displaced, hyperdynamic apex beat - LV dilatation from chronic volume overload

•Exertional dyspnoea, fatigue, palpitations - in chronic MR; AF common due to LA enlargement

⚠️

In acute MR post-MI, the murmur may be soft or absent because LA and LV pressures rapidly equalise, reducing the driving gradient for the regurgitant jet.

Investigations

🏆 Gold standard

•transthoracic echocardiography (TTE) - grades severity, assesses LV/LA size and function, pulmonary artery pressures

•ECG - P-mitrale (broad, bifid P wave), LVH, AF

•Chest X-ray - LA and LV enlargement, pulmonary venous congestion, Kerley B lines

•TOE - if TTE inadequate or pre-operative planning

Management

•Asymptomatic + preserved LV function - surveillance with serial echocardiography

•Symptomatic or LV dysfunction - refer for mitral valve repair (preferred over replacement)

•Heart failure symptoms - furosemide for symptomatic relief

•AF - anticoagulate (e.g. apixaban)

•Acute MR - emergency surgical intervention; high operative mortality

🎯

The EF paradox: in chronic MR, EF appears supranormal during compensation (LV ejects into low-pressure LA). An EF of ~48% in MR represents significant LV dysfunction - the threshold for concern is lower than in other conditions. Intervene before EF falls into the clearly abnormal range.

Complications

•Atrial fibrillation - LA dilatation; increases thromboembolism/stroke risk

•Pulmonary hypertension - chronically elevated LA pressure transmitted to pulmonary vasculature

•LV dysfunction/heart failure - chronic volume overload; often irreversible even after surgery

•Infective endocarditis - abnormal valve is a nidus for bacterial seeding

•Acute pulmonary oedema and cardiogenic shock - in acute MR; high mortality without emergency surgery