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4D Imaging of the Aortic Valve: Aortic Valvular Stenosis

Aortic valvular stenosis is narrowing of the aortic valve orifice that occurs when the valve leaflets do not open normally. Flow through the valve becomes turbulent and increases left ventricular work leading to concentric left ventricular hypertrophy.

Normal valve area is 3-4 cm2 in adults. An aortic valve area less than 2 cm2 is clinically important and a valve area less than 0.8 cm2 results in critical aortic stenosis.

Symptoms of aortic stenosis are angina, effort syncope and congestive heart failure. The presence of symptoms is associated with a poor prognosis and valve replacement is usually required.

Causes of aortic valvular stenosis include tricuspid valve degeneration, bicuspid aortic valve, congenital stenosis, rheumatic fever, systemic lupus erythematosus, and severe familial hypercholesterolemia.

Bicuspid valves occur in 2% of the population. One-half of patients with bicuspid valves develop at least mild aortic stenosis by the age of 50 years.

On imaging, the valve leaflets are thickened and have reduced mobility with narrowing of the orifice. The left ventricle is concentrically thickened. On echocardiography, valve orifice area is calculated from the velocity with the equation A2 = (A1 x V1) / V2 where A2 is the aortic valve area, A1 is the aortic outflow tract area, V1 is the velocity at the outflow tract and V2 is the velocity at the valve.

Therapy for critical aortic stenosis is to decrease the obstruction to left ventricular outflow by widening the orifice or replacing the valve. Percutaneous catheterization with aortic balloon valvuloplasty is a temporary palliative procedure for patients who cannot have valve replacement surgery. Replacement of the aortic valve is the definitive procedure and can result in improved left ventricular function.

In the Ross procedure, the patient’s pulmonic valve is used to replace the aortic valve and a prosthetic valve is used to replace the pulmonic valve (pulmonic valve transplantation). Using a native valve in the high pressure aortic system improves durability.

Alternatively, a heterograft bioprosthesis from porcine aortic valve leaflets or bovine pericardium is used to replace the aortic valve. These have limited durability after 10 years. Cryopreserved homografts from human donors are another possible source but are in limited supply.

Mechanical valves are durable but require anticoagulation. Bileaflet valves are the most common type currently used. Caged-ball and tilting-disk are the other types of prosthetic valves.

Source: Carabello BA, Crawford MH. Aortic Stenosis. In: Current Diagnosis and Treatment in Cardiology, 2nd edition. The McGraw-Hill Companies.