Congenital Aortic Valve Stenosis

Congenital aortic valve stenosis is obstruction at the aortic valve from a malformed valve. Bicuspid valve is the commonest cause and gives late stenosis, whereas unicuspid and dysplastic valves cause stenosis in infancy. Critical aortic stenosis in the neonate is duct dependent and fatal without treatment.

Bicuspid aortic valve is present in about 0.5 to 2% of the population and is the commonest congenital heart abnormality. About 9% of first degree relatives have a bicuspid valve. Valvular aortic stenosis forms about 5% of congenital heart disease, with a male to female ratio of about 4 to 1.

Bicuspid disease is associated with aortic dilatation and dissection, coarctation, and conditions such as Turner syndrome. Calcific stenosis appears 10 to 20 years earlier than in tricuspid valves, usually in the fifth to seventh decade.

Severity: severe stenosis is peak velocity of 4 m/s or more, mean gradient of 40 mmHg or more, or valve area of 1.0 cm2 or less (indexed 0.6 cm2/m2 or less). Very severe stenosis has peak velocity of 5 m/s or more.

Pathophysiology.

Valve leaflets are thickened, with fused commissures or a dysplastic structure. The left ventricle responds with concentric hypertrophy, which preserves ejection fraction at the cost of diastolic dysfunction, subendocardial ischaemia and arrhythmia.

In neonates with critical stenosis, the left ventricle may fail, giving endocardial fibroelastosis and systemic perfusion that depends on right-to-left flow through the duct. Closure of the duct causes shock.

Bicuspid valves are associated with abnormal aortic wall (medial degeneration, abnormal flow patterns), so aortic dilatation is independent of valve severity.

Neonates with critical stenosis present with heart failure, poor pulses and shock in the first days of life. Infants and children are usually asymptomatic, with an ejection systolic murmur and ejection click at the right upper sternal edge radiating to the neck. Symptoms in older children and adults are exertional dyspnoea, angina, syncope and heart failure, which appear late.

Signs: slow rising pulse, narrow pulse pressure, a soft or absent second heart sound, a sustained apex, a thrill and, with bicuspid valve, an early diastolic murmur of regurgitation.

• Echocardiography: valve morphology (number of cusps, raphe), peak and mean gradient, valve area by continuity equation, dimensionless velocity index, left ventricular size, wall thickness and function, aortic regurgitation, aortic root and ascending aorta diameter, and coarctation.
• ECG: left ventricular hypertrophy with strain. Chest radiograph: post-stenotic dilatation of the ascending aorta. Exercise testing in asymptomatic severe stenosis (a fall in blood pressure or symptoms indicates risk). Low dose dobutamine echocardiography for low flow low gradient disease. NT-proBNP.
• CT for calcium score (severe stenosis: women 1200 or more, men 2000 or more Agatston units) and aortic dimensions. MRI for the aorta and ventricular mass.
• Catheterisation is used mainly for balloon valvuloplasty, with a peak-to-peak gradient measured by catheter.
• First degree relative screening with echocardiography.

Differential diagnosis.

• Subvalvular (fibromuscular ridge, tunnel) and supravalvular aortic stenosis.
• Hypertrophic obstructive cardiomyopathy.
• Rheumatic and degenerative calcific aortic stenosis.
• Coarctation, mitral valve disease and hypoplastic left heart syndrome in neonates.

Critical neonatal stenosis (emergency).

• Alprostadil intravenously 0.05 to 0.1 microgram/kg/min to reopen the duct, then 0.01 to 0.03 microgram/kg/min. Watch for apnoea (intubate for transport), fever and hypotension.
• Support with dopamine 5 to 10 microgram/kg/min or adrenaline 0.05 to 0.3 microgram/kg/min, correct acidosis, and keep oxygen saturation 75 to 85%.
• Urgent balloon valvuloplasty in the first days of life, using a balloon-to-annulus ratio of 0.9 to 1.0. Surgical valvotomy is an alternative. Borderline left ventricles may need a single ventricle approach or a hybrid strategy. Hospital survival is about 80 to 90% in experienced centres.

Children and young adults.

• Balloon valvuloplasty when the catheter peak-to-peak gradient is 50 mmHg or more, or 40 mmHg or more with symptoms, ischaemic ECG changes at rest or on exercise, or planned pregnancy or competitive sport. Avoid it when moderate or severe aortic regurgitation is present. Complications are aortic regurgitation (moderate or more in about 10 to 15%), femoral artery injury, and restenosis. Give heparin 100 units/kg intravenously during the procedure.
• Surgery (valve repair, replacement, or the Ross procedure with pulmonary autograft) when balloon valvuloplasty is unsuitable or fails. The Ross procedure suits younger patients who wish to avoid anticoagulation, and carries a risk of autograft dilatation and homograft failure. Ross-Konno extends it to small annuli.

Adults. Replace the valve (surgical or transcatheter) for:

• Symptomatic severe stenosis.
• Asymptomatic severe stenosis with ejection fraction under 50%, abnormal exercise test (symptoms or fall in blood pressure), very severe stenosis (peak velocity 5 m/s or more) with low surgical risk, NT-proBNP over 3 times normal, or rapid progression (peak velocity rise of 0.3 m/s in one year).
• Severe stenosis at the time of other cardiac surgery.
• Surgical replacement is favoured under age 70 to 75 and in bicuspid disease with aortopathy. Transcatheter replacement suits older or high risk patients.
• Aortic surgery for the ascending aorta at 55 mm or more, or 50 mm or more with risk factors (family history of dissection, growth over 3 mm in a year, coarctation, hypertension), or 45 mm or more when undergoing valve replacement.

Medication.

• No drug slows progression, and statins do not alter it.
• Hypertension: ramipril 2.5 mg orally daily, titrated slowly to 10 mg (maximum 10 mg), with blood pressure, potassium and creatinine at 1 to 2 weeks; avoid hypotension. Beta blocker (metoprolol succinate 25 to 200 mg daily) for aortic dilatation or tachyarrhythmia.
• Congestion: furosemide 20 to 40 mg orally daily, used cautiously since the ventricle is preload dependent. Avoid nitrates and vasodilators in severe symptomatic stenosis.
• After mechanical valve replacement: warfarin to INR 2.5 (2.0 to 3.0) for a bileaflet aortic valve without risk factors, or 3.0 (2.5 to 3.5) with atrial fibrillation, previous thromboembolism, ejection fraction under 35% or thrombogenic valve design. After a bioprosthesis: aspirin 75 to 100 mg daily (warfarin for 3 months when surgically implanted in the mitral position, not applicable here).
• Endocarditis prophylaxis is not needed for the native bicuspid valve, but is given for prosthetic valves and after previous endocarditis: amoxicillin 2 g orally (children 50 mg/kg, maximum 2 g) 30 to 60 minutes before dental procedures; azithromycin 500 mg or doxycycline 100 mg with penicillin allergy.

Activity. Mild stenosis allows full activity. Moderate stenosis allows low to moderate sport after exercise testing. Severe stenosis or symptoms: avoid competitive and strenuous exercise.

Monitoring. Mild: echocardiography every 3 to 5 years. Moderate: every 1 to 2 years. Severe: every 6 months. Aortic imaging every 1 to 2 years when dilated. After balloon valvuloplasty or replacement: echocardiography before discharge and then yearly.

Referral and escalation. Refer neonates immediately to a paediatric cardiac centre. Refer children and adults with moderate or severe stenosis, aortic dilatation or symptoms to a valve or congenital heart service. Urgent referral for syncope, angina or heart failure.

Special groups.

• Pregnancy: mild and moderate stenosis is tolerated. Severe stenosis carries a high risk of heart failure and arrhythmia, and intervention before conception is advised for symptomatic or severe disease. During pregnancy, metoprolol is used for tachycardia, with balloon valvuloplasty for refractory heart failure. Avoid ACE inhibitors.
• Older adults: low gradient disease needs calcium scoring.
• Bicuspid valve relatives: echocardiography for first degree relatives.
• Region specific: rheumatic disease coexists as a cause of aortic stenosis, so check the mitral valve.