Any of the four heart valves may become diseased, but the most
commonly involved are the mitral and aortic valves. Only one valve may
be involved, but not infrequently two valves and occasionally three valves
may be affected. When a valve is diseased, it may become narrowed
(stenosed) or become leaky (incompetent or regurgitant); quite often the
valve will be both narrowed and leaky.
Obviously, if a valve is narrowed, this provides an obstruction to the
normal flow of blood and puts an extra strain on the heart. In the case of the
mitral valve this will cause the blood to dam up and fluid will collect in the
lungs causing congestion and shortness of breath. Obstruction of the aortic
valve will cause the pumping chamber to the body (left ventricle) to thicken
and increase its muscle bulk in response to the obstruction (left ventricular
hypertrophy). Only after some time will there be symptoms, usually
shortness of breath when the ventricle is unable to cope with the obstruction
any more, chest pain because there is not sufficient blood to supply the
greatly thickened muscle of the heart of dizziness because the obstruction is
so severe that the pumping chamber cannot eject enough blood to supply
adequate oxygen to the brain. Narrowing of the other two valves is rare in
adults.
If the valves are leaky this will also involve the heart in extra work
since in addition to pumping forward, as it is supposed to do, the heart is
wasting energy because some of the blood is going backwards as well.
Leaking of the mitral and aortic valves will cause the left ventricle to thicken and become enlarged; initially there will be no symptoms but later,
owing to the long-standing extra work, the pumping chamber will fail and
shortness of breath will occur. The back pressure on the lungs will mean
extra work for the right ventricle. If the right ventricle is unable to cope with
this it will fail and fluid will collect in the body causing swelling of the
ankles and abdomen. Leaking of the tricuspid valve will also cause the right
ventricle to be thickened and enlarged, and may lead to right ventricular
failure causing swelling of the ankles and abdomen.
The commonest cause of serious valve disease today is still rheumatic
fever that occurred 20-30 years ago. Rheumatic fever is now extremely rare
so that in years to come we would expect rheumatic heart valve disease to
become less common. Some people are born with an abnormal aortic valve.
Whilst it may never cause problems for most patients in some, particularly if
the valve becomes infected, stenosis and/or incompetence may develop over
the years.