Acute Severe Mitral Regurgitation

Acute severe mitral regurgitation is sudden, large regurgitant flow into a left atrium that has not had time to dilate, producing pulmonary oedema and low forward output. It differs from chronic regurgitation, in which compensation delays symptoms.

Epidemiology. It is uncommon but life threatening. Mortality is high without prompt valve intervention.

Causes and associations.

• Papillary muscle rupture or dysfunction after myocardial infarction.
• Chordal rupture: myxomatous degeneration (mitral valve prolapse), endocarditis, rheumatic disease, trauma and connective tissue disease.
• Leaflet perforation or destruction in infective endocarditis.
• Prosthetic valve dysfunction (dehiscence, leaflet failure, thrombosis).
• Stress cardiomyopathy, blunt chest trauma and acute left ventricular dilation.

Pathophysiology. A large regurgitant volume enters a small, non-compliant left atrium, so left atrial and pulmonary venous pressure rise sharply. Pulmonary oedema develops, while forward stroke volume falls. The left ventricle is of normal size and cannot compensate acutely.

Presentation is abrupt breathlessness, pulmonary oedema, orthopnoea, hypotension, tachycardia and shock. The murmur may be short and early, and may be soft or absent when pressures equalise. A third heart sound is present. The apex beat is not displaced.

Red flags.

• Pulmonary oedema with shock and a new murmur.
• Fever or recent infective endocarditis risk.
• Recent myocardial infarction or chest trauma.

Transthoracic echocardiography with Doppler (flail or perforated leaflet, eccentric jet, severity, left ventricular function), then transoesophageal echocardiography for mechanism and surgical planning. Chest radiograph (pulmonary oedema, sometimes unilateral), ECG, troponin, natriuretic peptide, cultures (three sets before antibiotics when endocarditis is possible) and lactate. Coronary angiography before surgery as indicated.

Differential diagnosis. Ventricular septal rupture, acute aortic regurgitation, acute pulmonary oedema of other cause, cardiac tamponade and myocardial infarction.

Stabilisation.

• Oxygen, non-invasive ventilation or intubation.
• Afterload reduction when systolic pressure allows (over 90 to 100 mmHg): nitroprusside 0.3 to 0.5 microgram/kg/min (maximum 10 microgram/kg/min, short term, with thiocyanate monitoring) or nitroglycerin 10 to 200 microgram/min.
• Intra-aortic balloon pump for hypotension.
• Inotrope (dobutamine 2.5 to 10 microgram/kg/min) or vasopressor (noradrenaline 0.05 to 0.5 microgram/kg/min) for shock.
• Furosemide 40 to 80 mg IV.
• Avoid beta blockers (which blunt compensatory tachycardia) and cardiac pacing to slow the rate.

Endocarditis. Take three sets of blood cultures, then start empirical antibiotics: vancomycin 25 to 30 mg/kg IV loading dose then 15 to 20 mg/kg every 8 to 12 hours (adjusted to level and renal function), plus gentamicin 3 mg/kg IV daily (for native valves), adjusted to renal function and levels, until organism is identified.

Definitive treatment. Urgent surgery (valve repair or replacement) for acute severe regurgitation with pulmonary oedema or shock, and early surgery for endocarditis with heart failure, uncontrolled infection or large vegetations. Transcatheter edge-to-edge repair is an option in patients who cannot have surgery.

Monitoring. Arterial pressure, pulmonary artery pressure, lactate, urine output, echocardiography and renal function.

Referral and escalation. Cardiac surgery, cardiology and cardiac intensive care at once.

Special groups. In pregnancy, manage with cardiology and obstetrics, and avoid nitroprusside if possible. In renal failure, adjust gentamicin and avoid nitroprusside accumulation.