Anatomy of the Heart Valves.
The pumping chambers of the heart are separated by valves
that open and close in sequence as blood flows through the
heart. Essentially this is to ensure blood flows forward through
the heart. As blood returns from the veins to the heart it
enters the right atrium from the large veins the superior
an inferior vena cava. The right atrium is separated from
the right ventricle by the tricuspid valve and blood is then
ejected in to the lung arteries (pulmonary arteries) through
the pulmonary valve. After picking up oxygen the blood returns
to the heart entering the left atrium which is separated from
the left ventricle by the mitral valve. The left ventricle
is the main pumping chamber and blood is ejected into the
aorta and then round the body through the aortic valve.
 |
|
Blood
flow through the heart during heart contraction |
Blood
flow through the heart during filling |
| |
|
| Click Images to Enlarge |
|
back to top
Heart Valve Disease
Heart valves may become narrowed (stenosed) and not let enough
blood through or may leak (regurgitant, incompetent) allowing
blood to go backwards. There are a number of causes of valve
disease including previous rheumatic fever (an inflammatory
disease of childhood), degeneration of the valve with age,
stretching of the valve with enlargement of the heart, infections
of the valve tissue during a disease called endocarditis o
occasionally as a complication of other heart disease such
as a heart attack. While any of the heart valves can be affected
it is more common for disease to affect the mitral and aortic
valves.
Mitral stenosis (narrowing) is invariably due to previous
rheumatic fever. Mitral regurgitation is often due to mitral
valve prolapse syndrome where the valve is too stretched and
prolapses backwards. This is a common condition in the population
at large but only severely affects a small proportion of people
with prolapse. Mitral regurgitation may also occur due to
stretching of the left ventricle after a heart attack or due
to heart failure.
Aortic stenosis may occur in young people as a congenital
abnormality but most frequently is due to degeneration and
calcification in older life. Aortic regurgitation is often
as a result of rheumatic fever and may be congenital or a
result of endocarditis.
back to top
Symptoms/Signs and Investigation
of Heart Valve Disease
There may be no symptoms for many years if valve disease is
mild and the heart adapts well to the extra strain. The commonest
symptom is breathlessness particularly on exercise or exertion.
Patients may also complain of palpitation and sometimes chest
pain. If the valve disease progresses heart failure may develop.
On examination patients frequently have a 'murmur' when doctors
listen to the heart with a stethoscope. This is a sound made
by turbulent blood flowing across an abnormal valve. A variety
of tests can be used to confirm valve disorders and to measure
progress. These include the ECG, a Chest X-ray and an Echocardiogram
(heart ultrasound scan). The latter is very useful in measuring
the extent of valve disease and any strain on the heart. Cardiac
catheter studies are done if there is any uncertainty or if
any form of surgery is planned.
Echocardiogram of aortic valve stenosis (calcified leaflets
arrowed)
LV: left ventricle. AO: aorta. LA: left atrium
LVOT: Left ventricular outflow tract AML: anterior mitral
leaflet
back to top
Treatment of Valve Disease
The appropriate treatment varies from patient to patient and
depends on the severity of the valve disease, the severity
of the symptoms and the findings of the various tests. Initially
if symptoms become more severe a variety of tablet treatments
may allow patients a full recovery. These include diuretics
(water tablets), digoxin (to steady the heart rhythm) and
vasodilator or ACE inhibitor drugs (to take the strain off
the heart.
back to top
Balloon Mitral Valvotomy (PTMC,
Mitral Valvuloplasty)
This is a way of treating Mitral Valve stenosis by splitting
the valve without major open heart surgery. Not all patients
are suitable for the procedure but it is highly successful
in patients with valves that can be stretched. It is done
in a similar way to a catheter test under local anaesthetic
usually via the artery and vein in the right groin. A tube
is passed up from the leg to the right atrium and then crossed
into the left atrium. A balloon is then steered across the
mitral valve which is gradually stretched and split open to
allow near normal flow of blood through the heart. The risks
of this procedure are low but may cause some leaking of the
mitral valve if it is over stretched. There is close monitoring
using echocardiography scans and catheter pressure measurements
throughout to avoid complications. If a suitable degree of
stretching is achieved the symptoms usually resolve. The narrowing
or stenosis of the mitral valve may recur but is a very slow
process and most patients who are successfully treated have
several years without symptoms.
back to top
Open Heart Surgery
This involves a general anaesthetic and a longer stay in hospital
but in many patients is the only way their heart valve disease
can be successfully treated. Although there are risks which
vary from person to person the long term results of heart
valve surgery are in general very good.
back to top
Heart Valve Replacement
Heart valve replacement refers to procedures aimed at replacing
your own heart valve, rather than repairing your own valve.
If a surgeon cannot repair a heart valve, the valve is removed
and replaced with an artificial (prosthetic) valve by sewing
it into the remaining tissue from the natural valve. Throughout
the world, 95% of all valve replacements are performed for
mitral or aortic valves. The mitral valve is positioned in
the heart's left side, between the left upper chamber (left
atrium) and the left lower chamber (left ventricle). The aortic
valve separates the left ventricle from the aorta (which carries
blood to the body).
Today, there are two types of prosthetic valves used for replacement
mechanical or tissue.
back to top
Mechanical Valves
A mechanical valve is carefully designed to mimic the native
heart valve. It has a ring, like your own natural heart valve,
to support the leaflets which are made of metal. Like your
own heart valve, the mechanical valve opens and closes with
each heartbeat, permitting proper blood flow through the heart.
To prevent any blood clots from developing requires you to
take anticoagulation medicine (blood thinners) daily. The
dosage of this medication is different for each person, so
you will be closely monitored to make sure you are on the
correct dosage for you. Regular blood tests will be performed
at the physician's office, an anticoagulation clinic, or at
home with a specialised testing kit.
back to top
Tissue Valves (Bioprostheses)
The tissue valve is a native valve taken from an animal. Once
the tissue is explanted (removed), it is chemically treated
and prepared for human use. Some tissue valves have a frame,
or stent, that supports the valve, and some valves are stentless
(no framework). A very thin polyester mesh cuff is sewn around
the outside of the valve for easier implantation. Eliminating
the stent makes it possible for the surgeon to implant a larger
valve. Larger valves generally provide more surface area for
blood flow; this allows more blood to flow through the valve
to accommodate the body's needs.
back to top
Homografts
A homograft or allograft is a human valve obtained from a
donor. This type of valve is particularly beneficial for pregnant
women and children, because it does not require long-term
anticoagulation therapy. In addition, it can provide excellent
haemodynamic performance, allowing for natural function of
the surrounding structures. Because the availability of these
valves depends on donors, supply is limited.
back to top
Valve Repair
In some cases particularly of mitral valve disease it is possible
for the surgeon to repair the valve by stretching it or tightening
any leakage. Only certain people are suitable for valve repair
but keeping your own valve is usually advantageous in maintaining
the hearts normal function and sometimes avoiding the need
for long term anticoagulation.
back to top
