Download Valves of the Heart

Valves of the Heart
As mentioned earlier, blood flows through the heart in one direction.
What prevents blood from flowing in the opposite direction? The answer
is the heart’s valves. These valves maintain unidirectional flow by
preventing backward (retrograde) flow when the pressure gradients
change during the heart cycle. These valves are found in matched pairs
in two locations of the heart. The first set, the atrioventricular (AV)
valves, separate the atria from the ventricles. The second,
the semilunar valves, are located between the ventricles and the
arteries they feed.
Following the path of blood flow through heart, the first valve is
the tricuspid valve found separating the right atrium from the right
ventricle. This AV valve is so named because it has three flaps:
the anterior cusp, the medial cusp, and the posterior cusp. On
the ventricle side of the valve are long muscular cords, called chordate
tendinae, that extend from the inferior side of each cusp. The chordate
tendinae attach to each cusp on one end and to the papillary muscle,
which is connected to the inner wall of the ventricle, on the other end.
These muscles prevent the valves from inverting back into the atria
during ventricular contraction.
Most of the blood flows passively into the atria, through the tricuspid
valve, and into the right ventricle. Atrial contractions then push most of
the remaining atrial blood into the ventricle. As the right ventricle fills,
the pressure inside it increases. This increased pressure, coupled with
the right atria moving into its relaxation phase, causes the ventricular
pressures to be greater than atrial pressures. This causes the tricuspid
AV valves to close. In this closed position, the chordae tendinae that are
attached to the ventricular side of the valves are fully extended and taut,
like a stretched bungee cord. The chordae tendinae prevent the higher
pressure in the ventricle from forcing the valve to open back into the
atria, thus preventing the backflow of blood through the tricuspid valve.
As the blood flows from the right ventricle into the pulmonary artery, it
passes through the pulmonary semilunar valve (pulmonary valve).
Opposite to the tricuspid, the pulmonary semilunar valve remains
closed when the ventricle is filling and opens during ventricular
contraction. Again, this is because the valves work by opening when the
pressure is higher on their proximal side and close when the pressure is
higher on their distal side.
On its return from the lungs, blood enters the left atrium. As the blood
passes from the left atrium into the left ventricle, it passes through
the bicuspid valve, often referred to as the mitral valve. This valve
is similar in structure and function to the tricuspid, but only contains
two cusps, the anterior and posterior cusps. It, too, is open when the
pressure in the atria exceeds the ventricle and it, too, has chordae
tendinae and papillary muscles that prevent its inversion upon
ventricular contraction. The release of blood from the left ventricle into
the aorta is regulated by the aortic semilunar valve, which is most
commonly referred to as the aortic valve. It is similar in structure and
function to the pulmonary semilunar valve. Because they regulate the
flow of blood through the heart and prevent its backflow, these valves
are indispensable for the proper function of the heart.
Diseases of the Heart: Ruptured Chordae Tendinae
The chordae tendinae perform an important function by keeping the
cusps of the atrioventricular valves tethered to the interior wall of the
ventricles. Without these tendons, and their associated papillary
muscles, the valves could become inverted when the pressure in the
ventricle increases, causing the blood to rush back into the atria.
Although this happens infrequently, the chordae tendinae can rip or
rupture. When this happens, the cusps of the tricuspid or mitral valves
are no longer properly tethered to the wall of the ventricle. As the blood
presses back against the valves during ventricular contraction, the valves
may not remain closed. If many of these connections are ruptured or if
the thicker ones are affected, the valves can open in the reverse
direction, and blood can backflow into the atria. This results in
increased pressure in the atria and, if the backflow is significant enough,
congestive heart failure could develop.
Rupture of the chordae tendinae occurs when a patient suffers from a
myocardial infarction (heart attack), heart valve infection, or from
trauma to the chest. Damage can range from minor to major depending
on the number of chordae affected. It is diagnosed by hearing a murmur,
or a characteristic whooshing noise, upon auscultation (listening to
heart sounds with a stethoscope or other device) of the heart. Ruptured
chordate tendinae, and their associated conditions, commonly lead to
heart failure.
Rupture of the chordae tendinae attached to the mitral valve is most
common, although rupture of those bound to the tricuspid valve can
also occur. Rupture of the mitral valve chordae tendinae can result in a
rapid increase in left atrial pressure. This can subsequently increase the
pressure in the pulmonary circulation, ultimately producing pulmonary
edema; which is retention of fluid in the lungs. An echocardiogram can
provide a more detailed look into the condition of the heart and the
degree of damage to the chordae tendinae.