Congenital Mitral Valve Disease

Congenital mitral valve disease is malformation of the mitral leaflets, chordae, papillary muscles or annulus present from birth. It causes stenosis, regurgitation or both, and presents from infancy to adult life.

Stenosis types: supravalvular mitral ring, typical (commissural fusion), hypoplastic annulus, parachute mitral valve (a single papillary muscle), double orifice valve and arcade (hammock) valve. Regurgitation types: cleft anterior leaflet (isolated or in atrioventricular septal defect), leaflet dysplasia or prolapse, elongated or absent chordae, and annular dilatation.

Isolated lesions are uncommon and account for under 1% of congenital heart disease. Most coexist with other left sided obstruction, such as subaortic stenosis, aortic stenosis or coarctation (Shone complex), or with atrioventricular septal defect, particularly in Down syndrome.

Pathophysiology.

Stenosis raises left atrial and pulmonary venous pressures, which cause pulmonary congestion, pulmonary hypertension and right ventricular failure, and can lead to irreversible pulmonary vascular disease if untreated. Left atrial dilatation causes atrial fibrillation.

Regurgitation causes left atrial and ventricular volume overload, ventricular dilatation and eventually dysfunction.

Severity guides timing: rapid progression is common with a hypoplastic annulus or multiple levels of obstruction, and early repair prevents pulmonary vascular disease.

Infants: tachypnoea, feeding difficulty, sweating, failure to thrive, recurrent chest infections, wheeze, irritability, and a loud second heart sound. Children and adults: exertional dyspnoea, fatigue, palpitations, haemoptysis and atrial fibrillation. Murmurs: a low pitched mid-diastolic rumble with a loud first sound (stenosis), or an apical holosystolic murmur radiating to the axilla (regurgitation). Right sided signs appear with pulmonary hypertension.

• Echocardiography (two- and three dimensional): annulus size (z-score), leaflet mobility and thickness, commissures, papillary muscle number and position, chordal length, supravalvular ring, cleft and jet direction. Doppler: mean diastolic gradient, pressure half time (valve area is about 220 divided by half time), left atrial size, left ventricular size and function, and pulmonary pressure.
• Look for associated lesions: subaortic stenosis, aortic valve and arch obstruction, septal defects and pulmonary vein anomalies.
• Cardiac MRI or CT for complex anatomy and pulmonary veins.
• Cardiac catheterisation when gradient, pulmonary vascular resistance or reversibility needs measurement.
• ECG: P mitrale, right ventricular hypertrophy, atrial fibrillation. Chest radiograph: left atrial enlargement and pulmonary venous congestion.
• Genetic assessment when syndromic.

Differential diagnosis.

• Cor triatriatum sinister and pulmonary vein stenosis.
• Rheumatic mitral stenosis in an older child.
• Hypoplastic left heart variants, subaortic obstruction and left atrial myxoma.
• Infective endocarditis causing acute regurgitation.

Medical therapy (symptoms and bridging to repair).

• Furosemide 1 to 2 mg/kg orally every 8 to 12 hours (maximum 6 mg/kg daily); monitor electrolytes, creatinine and urine output; reduce frequency in renal impairment.
• Spironolactone 1 to 3 mg/kg orally daily in 1 to 2 doses; check potassium at 1 and 4 weeks.
• Stenosis with tachycardia or atrial fibrillation: propranolol 0.5 to 1 mg/kg orally every 8 hours (maximum 4 mg/kg daily, or 160 mg daily in adults) to lengthen diastole; monitor heart rate, blood pressure and glucose in infants; avoid in asthma. Adult regimens: metoprolol succinate 25 to 200 mg daily.
• Regurgitation with ventricular dilatation: enalapril 0.05 to 0.1 mg/kg orally daily in 1 to 2 doses, increased gradually to a maximum 0.5 mg/kg daily (adults ramipril 2.5 to 10 mg daily); monitor blood pressure, potassium and creatinine at 1 to 2 weeks. Avoid afterload reduction when subaortic obstruction coexists.
• Atrial fibrillation: anticoagulate (warfarin to INR 2.0 to 3.0) and control rate; avoid direct oral anticoagulants when stenosis is moderate or severe.
• Endocarditis prophylaxis only for prosthetic material, previous endocarditis or unrepaired cyanotic disease; maintain dental hygiene.

Intervention.

• Indications: symptoms, pulmonary hypertension, progressive left atrial or ventricular dilatation, or ventricular dysfunction (ejection fraction under 60% in regurgitation).
• Stenosis: surgical resection of the supravalvular ring (excellent results), papillary muscle splitting, commissurotomy and chordal fenestration. Balloon valvuloplasty is seldom suitable except for pliable fused commissures. Replacement is a last resort in infants because of annular size and anticoagulation needs.
• Regurgitation: repair is preferred (cleft closure with annuloplasty, chordal procedures, leaflet augmentation); replacement for failed repair.
• Mechanical valves require warfarin to INR 3.0 (2.5 to 3.5); in infants, enoxaparin 1.5 mg/kg subcutaneously every 12 hours is a bridge, with anti-Xa monitoring 0.5 to 1.0 units/mL at 4 hours. Bioprosthetic valves: warfarin for 3 to 6 months, then aspirin 3 to 5 mg/kg daily in children (75 to 100 mg in adults).
• Treat associated lesions at the same operation.

Monitoring. Clinical review and echocardiography every 3 to 6 months in infants with significant disease, every 6 to 12 months in children, and yearly in adults; INR as directed; ECG for atrial arrhythmia; pulmonary pressure estimates at each review.

Referral and escalation. Refer every suspected case to paediatric cardiology and congenital cardiac surgery. Urgent referral for heart failure, rising pulmonary pressure, or any infant with feeding failure.

Special groups.

• Pregnancy: stenosis with a high gradient causes pulmonary oedema in the second and third trimesters; use beta blockade, diuretics and bed rest; avoid warfarin from 6 to 12 weeks (low molecular weight heparin instead); deliver in a specialist centre.
• Relatives: echocardiography for first degree relatives, since familial clustering occurs.
• Children: weight based dosing; growth and development monitoring; plan valve choice with growth in mind.