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Back to Cardiovascular Diseases
Aortic valve stenosis
Causes and risk factors
A number of conditions contribute towards aortic stenosis.
Three conditions that are known to cause aortic stenosis are:
Valvular causes
1. Calcification of a bicuspid valve
Bicuspid aortic valve is the most common cause of aortic
stenosis in patients under age 65. Normal aortic valves have
3 thin leaflets called cusps. About 2% of people are born
with aortic valves that have only 2 cusps (bicuspid valves).
Although bicuspid valves usually do not impede blood flow
when the patients are young, they do not open as widely as
normal valves with 3 cusps. The turbulent blood flow causes
excessive wear and tear leading to calcification, scarring,
and reduced mobility of the valve leaflets over time. About
10% of bicuspid valves become significantly narrowed,
resulting in the symptoms and heart problems of aortic stenosis.
2. Senile calcific aortic stenosis
The most common cause of aortic stenosis in patients 65
years and over is called "senile calcific aortic stenosis."
With aging, protein collagen of the valve leaflets is
destroyed, and calcium is deposited on the leaflets. Once
valve leaflet mobility is reduced by calcification,
turbulence across the valve increases, causing scarring,
thickening, and stenosis of the valve. Why this aging
process progresses to cause significant aortic stenosis in
some patients but not in others is not known.
3. Rheumatic fever
Rheumatic fever rarely causes isolated aortic stenosis. Rheumatic fever is a condition resulting from untreated
infection by group A streptococcal bacteria. Damage to valve
leaflets from rheumatic fever causes increased turbulence
across the valve and more damage. The narrowing from
rheumatic fever occurs from the fusion of the commissures of
the valve leaflets. Rheumatic aortic stenosis usually occurs
with some degree of aortic regurgitation. Under normal
circumstances, the aortic valve closes to prevent blood in
the aorta from flowing back into the left ventricle. In
aortic regurgitation, the diseased valve allows leakage of
blood back into the left ventricle as the ventricular
muscles relax after pumping. These patients also have some
degree of rheumatic damage to the mitral valve.
Subvalvular causes
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Subvalvular aortic stenosis
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Hypertrophic obstructive cardiomyopathy
Pathogenesis
Valvular aortic stenosis results in chronic left ventricular
pressure overloading. At any stage of life, however, the natural
history of aortic stenosis largely reflects the functional
integrity of the mitral valve. As long as adequate mitral valve
function is maintained, the pulmonary bed is protected from the
systolic pressure overloading imposed by aortic stenosis. In
contrast to mitral valve disease where the pulmonary circuit is
directly involved, compensatory concentric left ventricular
hypertrophy allows the pressure overloaded ventricle to maintain
stroke volume with modest increases in diastolic pressure, and
patients can remain asymptomatic for many years.Eventually, left ventricular hypertrophy results in either
diastolic dysfunction with the onset of congestive symptoms or
myocardial oxygen needs in excess of supply with the onset of
angina.
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