Heart Valves

The Fibrous Skeleton

Although the heart is a contractile organ, there are other tissues besides the cardiac muscle fibers.  There are neural structures such as the nodes and fibers of the cardiac conductionThe transmission of nerve impulses along neurons. system.  There is also collagenA structural protein in the dermis that provides strength and elasticity. and elastin connective tissue acting as a mushy skeleton for the innervated myocardium.  This connective tissue, stained blue in the picture above, is called the fibrous skeleton.  It’s like a big tendon. As the myocardium contracts, it pulls against this fibrous skeleton. This action is similar to how a skeletal muscle would pull against a bone.  And over the lifetime of the heart, this is what prevents stretching of the myocardium

Valves

These valves are extensions of the fibrous skeleton. As the myocardium contracts, it pulls on that fibrous skeleton. It’s similar to when you contract your bicep and pull your lower arm to your upper arm. That’s what causes the opening and closing of the valves. The purpose of any of these valves is to prevent backflow. 

Atrioventricular Valves

These white structures are the AV valves which ensure one-way motion through the heart, from the atria to the ventricles.

The atrioventricular (AV) valves differ structurally. On the right side of the heart, the tricuspid valve separates the right atrium from the right ventricle. On the left side, the bicuspid valve (also called the mitral valve) separates the left atrium from the left ventricle. These valves have two or three flaps. The chordae tendineae, or “heartstrings,” attach the flaps to the bottom of the ventricles. When the valves close, the chordae tendineae tighten to secure the flaps. The papillary muscles stabilize the flaps as they contract with the heart. This action causes the first heart sound, the “lub.“

A faulty valve can lead to regurgitation.  If an AV vale is faulty, blood in the ventricles will backflow into the atria, called atrial regurgitation.  This causes a murmur between the first and second heart sounds. However, murmurs do not always indicate faulty valves. They can be caused by other heart issues. One example is a ventricular septal defect (VSD). This also causes a murmur between the first and second heart sounds.

Semilunar Valve

The semilunar (SL) valves, which include the pulmonary and aortic valves, are structurally similar, each with three flaps. When the heart contracts, these valves open to allow blood flow into the pulmonary artery and aorta. They cause the second heart sound, the “dup.” Faulty semilunar valves cause backflow from these vessels to the ventricles called ventricular regurgitation.  This leads to a murmur between the second and first heart sounds.  But, again, other things can cause this type of murmur. Causes might include a hole between the atria. Another possibility is a patent foramen ovale. 

Heart Sounds

This is not an EKG.  This is an audiogram.  Each of these squiggles is the sound of valves closing.  This is the first heart sound of the AV valves closing. This is the second heart sound of the SL valves closing.  Between the first and second heart sounds, the heart is pumping or in systole.  Between the second and first heart sounds the heart is filling or in diastole.  No, these phases are not equal in duration.  The heart ejects blood a whole lot faster than it fills with blood.  This is why diastole is longer than systole. 

If a valve fails to close correctly, I will hear blood flowing through it between these heart sounds.  I shouldn’t hear anything, but even the slightest opening of a valve when it should be closed causes noise.  It’s kind of like cracking a window in the car when you are driving on the highway.  Even a small opening creates a lot of noise.  Murmurs reflect abnormal blood flow in the heart and are heard between these heart sounds. 

This definition of a murmur is simply the result of abnormal blood flow. Therefore, blood flow through a ventricular septal defect will also create sound. A hole in the interventricular septum would similarly create sound.  And, it does.  It mimics the sound of a systolic murmur. As the heart contracts, blood flows from the left ventricle to the right ventricle. 

Heart Murmurs

The simplest definition of a murmur is abnormal blood flow.  The most common cause is a faulty valve, but that’s not a 100% assumption.  On a personal note, if my mother’s cardiologist had taken more time, he might have considered her condition more carefully. He might not have been so quick to diagnose her with a mitral valve murmur. Then maybe he wouldn’t have missed her PFO. 

A systolic murmur occurs when the heart is pumping. It could result from either AV valve not closing correctly.  This would cause atrial regurgitation.  A diastolic murmur occurs when the heart is filling. It may result from either SL valve not closing correctly, as pictured here.  This would cause ventricular regurgitation.