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Cardiac
Main Page
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.
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