Aortic Stenosis (cont.)
What causes aortic stenosis?
In adults, three conditions are known to cause aortic stenosis.
- Progressive wear and tear of a bicuspid valve present since birth (congenital).
- Wear and tear of the aortic valve in the elderly.
- Scarring of the aortic valve due to
rheumatic fever as a child or young adult.
Bicuspid aortic valve is the most common cause of aortic stenosis
in patients under age 65. Normal aortic valves have three thin leaflets
called cusps. About 2% of people are born with aortic valves that
have only two 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 three cusps. Therefore,
blood flow across the bicuspid valves is more turbulent, causing
increased wear and tear on the valve leaflets. Over time, excessive
wear and tear leads to calcification, scarring, and reduced mobility
of the valve leaflets. About 10% of bicuspid valves become
significantly narrowed, resulting in the symptoms and heart problems of aortic
stenosis.
The most common cause of aortic stenosis in patients 65 years of age 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. Turbulence across the valve increases causing scarring, thickening, and stenosis of the valve once valve leaflet mobility is reduced by calcification. Why this aging process progresses to cause significant aortic stenosis in some patients but not in others is unknown. The progressive disease causing aortic calcification and stenosis has nothing to with healthy lifestyle choices, unlike the calcium that can deposit in the coronary artery to cause heart attack.
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 (melting together) of the edges (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. Rheumatic heart disease is a relatively uncommon occurrence in the United States, except in people who have immigrated from underdeveloped countries.
Next: How does aortic stenosis affect the left ventricle pump? »
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