Lucan · Conditions

Mitral regurgitation

Australian guidance: CSANZ Valvular Heart Disease

1. Definition and epidemiology

Mitral regurgitation (MR) is the pathological backflow of blood from the left ventricle into the left atrium during systole, caused by incompetence of the mitral valve apparatus. It is the most common valvular abnormality in Australia and worldwide, with clinically significant MR estimated to affect approximately 2 to 3% of the general population. Prevalence increases markedly with age, and both primary and secondary (functional) forms contribute to the burden of disease encountered in Australian hospitals.

2. Pathophysiology

MR is classified as primary or secondary. In primary (degenerative) MR, the structural defect lies within the valve apparatus itself: myxomatous degeneration in mitral valve prolapse causes leaflet billowing and chordal redundancy; rheumatic disease causes fibrosis and leaflet retraction; infective endocarditis produces leaflet perforation or chordal rupture; and acute MI can rupture a papillary muscle, precipitating sudden severe MR. In secondary (functional) MR, the leaflets are structurally normal but the annulus dilates and the papillary muscles are displaced outward because of left ventricular dilatation or inferior wall infarction, preventing leaflet coaptation. Regurgitant volume reduces forward stroke volume and causes volume overload of the left atrium and left ventricle. In chronic compensated MR, eccentric hypertrophy and left atrial dilatation accommodate the added volume at near-normal filling pressures. When compensation fails, left ventricular end-systolic dimension rises, ejection fraction declines, and elevated left atrial pressure causes pulmonary venous congestion and eventually pulmonary hypertension. In acute severe MR, there is no time for compensatory dilatation; abrupt pressure transmission to a non-compliant left atrium causes acute pulmonary oedema and haemodynamic collapse. (Robbins Ch 12)

3. Clinical presentation and diagnostic criteria

Chronic compensated MR is often asymptomatic for years or decades. Symptoms develop insidiously and include dyspnoea on exertion, fatigue, reduced exercise tolerance, and eventually orthopnoea and paroxysmal nocturnal dyspnoea as left ventricular function deteriorates. Palpitations suggest atrial fibrillation (AF), which is a frequent complication of chronic left atrial dilatation.

On auscultation, primary MR produces a holosystolic (pansystolic) murmur best heard at the apex, radiating to the axilla, and graded according to the Levine scale. In posterior leaflet prolapse the murmur may radiate anteriorly toward the sternum. Mitral valve prolapse produces a mid-systolic click followed by a late systolic murmur that moves earlier with standing and later with squatting. A third heart sound and soft first heart sound are features of severe MR. The apex beat is displaced laterally in left ventricular dilatation. Acute severe MR may present with acute pulmonary oedema and cardiogenic shock; the murmur may be short and decrescendo rather than holosystolic due to rapid pressure equalisation.

The diagnosis is established by transthoracic echocardiography (TTE), which provides valve morphology, leaflet motion, regurgitant volume, effective regurgitant orifice area (EROA), and left ventricular and atrial dimensions. Severity grading is based on integrated criteria: severe primary MR is defined by EROA 40 mm2 or greater, regurgitant volume 60 mL or greater per beat, regurgitant fraction 50% or greater, and vena contracta width 7 mm or greater on TTE.

4. Investigations and AU-specific cutoffs

The investigation sequence in suspected MR proceeds as follows.

Transthoracic echocardiography is the first-line and most important investigation. It confirms MR, defines aetiology (degenerative, rheumatic, functional), grades severity by quantitative Doppler parameters, and assesses left ventricular systolic function (left ventricular ejection fraction, LVEF) and size, left atrial volume, and the presence of pulmonary hypertension. TTE should be repeated every one to two years in moderate MR and six to twelve monthly in severe asymptomatic MR to track left ventricular dimensions and function.

Transoesophageal echocardiography (TOE) is performed when TTE image quality is suboptimal, when surgical repair is planned (to define repair anatomy and guide intraoperative assessment), or when infective endocarditis is suspected as the cause of acute MR.

A 12-lead ECG may show left atrial enlargement (broad notched P waves in lead II, negative terminal deflection of P in V1) and AF. Chest X-ray demonstrates left ventricular and left atrial enlargement and, in decompensated disease, pulmonary venous congestion and interstitial oedema. Cardiac MRI is used when echocardiographic quantification is discordant or when accurate regurgitant fraction measurement is needed for surgical planning. Exercise stress testing can unmask exertional symptoms and provide objective functional data in apparently asymptomatic patients. Brain natriuretic peptide (BNP) or N-terminal pro-BNP (NT-proBNP) should be measured when symptoms are equivocal; elevated levels correlate with disease severity and predict adverse outcomes.

5. Management

Management is guided by symptom status, severity, and left ventricular systolic function. CSANZ Valvular Heart Disease guidance aligns with ESC 2021 valve guidelines; thresholds below are consistent with that framework.

Indications for intervention in primary MR: symptomatic severe MR with LVEF greater than 30% warrants prompt intervention. Asymptomatic severe MR with LVEF 60% or less or left ventricular end-systolic diameter (LVESD) 45 mm or greater is an indication for surgery, as these cutoffs mark the threshold of impending decompensation. Asymptomatic severe MR with new-onset AF or resting pulmonary systolic pressure above 50 mmHg also warrants early intervention. Mitral valve repair (leaflet reconstruction, annuloplasty ring) is strongly preferred over replacement when durable repair is achievable, as it preserves left ventricular geometry and avoids long-term anticoagulation; experienced centres achieve repair in over 95% of posterior leaflet prolapse cases.

Transcatheter edge-to-edge repair (TEER, for example MitraClip) is an alternative for high-surgical-risk primary MR and is an increasingly used option for selected patients with symptomatic secondary MR despite optimal medical therapy.

In secondary MR, the priority is optimal medical therapy of the underlying heart failure. Guideline-directed medical therapy (GDMT) for heart failure with reduced ejection fraction (ACE inhibitor or ARB or ARNI, beta blocker, mineralocorticoid receptor antagonist, SGLT2 inhibitor) reduces left ventricular volume overload and frequently reduces secondary MR severity, sometimes averting the need for valve intervention. Cardiac resynchronisation therapy should be offered when QRS duration is 130 ms or greater and LVEF is 35% or less, as it improves left ventricular synchrony and can reduce secondary MR.

6. Pharmacology and AU PBS notes

Medical therapy does not halt progression in chronic primary MR and is not a substitute for timely surgery.

Vasodilators (ACE inhibitors, ARBs) are indicated when hypertension coexists or when surgery is not feasible; they have not been shown to delay surgery in normotensive chronic primary MR. In acute severe MR with haemodynamic compromise, nitroprusside reduces afterload and improves forward output; an intra-aortic balloon pump may bridge to emergency surgery.

In secondary MR the full heart-failure drug regimen applies. Frusemide is the preferred loop diuretic in Australia (not furosemide) and is used to manage congestion. Spironolactone 25 to 50 mg daily (PBS authority available for heart failure with LVEF 40% or less) is first-line among mineralocorticoid receptor antagonists. Sacubitril/valsartan (Entresto) is PBS-listed with streamlined authority for HFrEF with LVEF 40% or less after failure or intolerance of ACE inhibitor/ARB.

Anticoagulation: when AF complicates MR, long-term anticoagulation is indicated to prevent thromboembolism. Direct oral anticoagulants (DOACs) are appropriate for AF with native MR; warfarin with a target INR of 2 to 3 is required for AF with mechanical mitral prostheses, as DOACs are contraindicated in this setting.

7. Complications and monitoring

Key complications include:

Irreversible left ventricular systolic dysfunction develops insidiously if intervention is delayed beyond the thresholds above; surgery after LVEF falls below 30% carries high risk and incomplete functional recovery.

Atrial fibrillation occurs in up to 30% of patients with longstanding severe MR due to chronic left atrial pressure and volume overload; onset of AF is an indication to reassess the timing of intervention.

Pulmonary hypertension is an adverse prognostic marker and may complicate post-operative recovery.

Infective endocarditis: patients with native mitral valve disease are at moderate risk; antibiotic prophylaxis is no longer routinely recommended by Australian guidelines for native valve disease except for high-risk populations (prior endocarditis, prosthetic valve, or certain congenital conditions). Patients should be counselled on dental hygiene and prompt medical review for unexplained fever.

Heart failure with progressive left ventricular dilatation and reduced ejection fraction is the end-stage complication of untreated or late-treated severe MR.

Surveillance schedule: mild MR requires TTE every three to five years; moderate MR every one to two years; severe asymptomatic MR every six to twelve months with clinical review. Patients with mechanical prostheses require lifelong warfarin monitoring with target INR 2.5 to 3.5 and annual TTE.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.