Heart Valves: Structure, Function, and Diseases

Heart

The heart is one of the important human organs that helps in maintaining a constant flow of blood throughout the body. It is through the blood that oxygen and nutrients are delivered to cells and tissues. Removal of waste products too takes place through blood. Heart valves also play an important role in blood circulation.

The heart wall consists of three layers of tissue- the pericardium, endocardium, and myocardium. It has four chambers- two atria (chambers that receive blood) and two ventricles (chambers that pump blood). The blood flow inside the heart is regulated by the four valves known as mitral, aortic, tricuspid, and pulmonary valves. The tricuspid and mitral valves keep a tab on the blood flow from the atria into the ventricles. The aortic and pulmonary valves, on the other hand, control the blood flow out of the ventricles.

 

Heart Valves

Valves are thin membrane-like structures found inside the heart. They regulate the flow of blood by their opening and closing. When open, they allow blood flow and when closed, they prevent the backflow of blood. Valves ensure the unidirectional flow of blood through the heart.

heart valves

The Location of Heart Valves

Tricuspid Valve: between the right ventricle and right atrium

Mitral Valve:  between the left ventricle and left atrium

Pulmonary Valve: between the right ventricle and pulmonary arteries

Aortic Valve: between the left ventricle and aorta

 

Structure and Function of Heart Valves

Aortic Valve

Cardiac valves regulate the one-way flow of blood through the chambers of the heart and to the blood vessels. They prevent the backward flow of blood in this process. The aortic valve, located between the left ventricle and aorta, is made of three flaps of thin tissue called cusps. The three cusps are the left coronary cusp, the right coronary cusp, and the non-coronary cusps.

When closed, this valve separates the left ventricle from the aorta. Aorta supplies blood to the human body. During systole, the aortic valve opens and blood flow from the left ventricle into the aorta. During this time, the left ventricle contracts and the aortic valve remains open. At the time of diastole, the left ventricle relaxes and the aortic valve gets closed. This helps the blood to remain in the aorta and thus, prevents backflow of the same. During the same diastole, the blood flows into the left ventricle from the left atrium through the mitral valve. This is the process through which the left ventricle gets refilled for the next contraction.

Sinus of Valsalva

Sinuses of Valsalva is an aortic sinus; a dilation on the aorta just above the aortic valve. Within this, the inlets of the coronary artery system are found. Usually, there are three aortic sinuses (one is anterior and the other two, posterior). During the diastole, the blood fills the aortic sinuses and through the coronary arteries, it gets supplied to the myocardium.

Mitral Valve

It is a bicuspid valve that has two leaflets. The anterior leaflet is called septal and the posterior one is the lateral leaflet. The word mitral comes from Mitra or bishop’s hat (it has two tips). It’s also called the atrioventricular valve. Between the  left ventricle and left atrium, there is the mitral valve. There is a subvalvular apparatus found beneath the mitral valve which prevents valve prolapse.

Subvalvular Apparatus

This apparatus consists of chordae tendineae and papillary muscles. The valve is anchored on the wall of the ventricle by the chordae tendineae. These are small tendons which prevent the valve leaflets from inverting, thus barring the backflow of blood. They are inelastic. The chordae tendineae are attached to papillary muscles on one end and the valve cusps on the other.

Papillary muscles anchor chordae tendineae and are finger-like projections on the wall of the ventricle. The connection between chordae tendineae and papillary muscles provide the tension which holds the valve in position and prevents valve prolapse. Subvalvular Apparatus has no role to play in the opening and closing of the valve. The valve closure takes place entirely due to the pressure gradient across the valve which occurs when blood gets pumped from high pressure to low-pressure areas.

Pulmonary Valve

Between the right ventricle and the pulmonary artery, there is the pulmonary valve. The exact position is at the base of the pulmonary artery at the point where it leaves the right ventricle. It is also called the right semilunar valve and is made up of three leaflets. Two are attached to the septum and the third one is the anterior leaflet. The cusps are attached to the arches of the cardiac skeleton at the base of the pulmonary artery. The cusps are made of a central thick fibrous part covered in endocardial folding. This folding gives the nodules and lunules on the valve. This feature helps in the tight apposition of cusps when closed.

Tricuspid Valve

Between the right atrium and the right ventricle, there is the tricuspid valve. It stops the backflow of blood. An alternate name for the tricuspid valve is the right atrioventricular valve. It consists of three leaflets (cusps). The anterior leaflet is the largest one and is known as the infundibular or anterosuperior leaflet. The other two are inferior or marginal leaflet (posterior leaflet) and medial leaflet (septal leaflet). The cusps are connected to papillary muscles through the chordae tendineae. The tricuspid valve prevents the flow of blood into the right atrium from the right ventricle.

 

The Steps in the Passage of Blood through the Heart and How the Valve Controls the Flow

Through the open tricuspid valve blood flow from the right atrium to the right ventricle. When the mitral valve is open blood flows from the left atrium into the left ventricle. The tricuspid valve closes when the right ventricle is full, it prevents the backflow of blood into the atrium when the ventricle contracts. The mitral valve closes when the left ventricle is full and prevents the backflow of blood into the left atrium. The contraction of the right ventricle forces the pulmonic valve to open. through this opening blood flows from the right ventricle into the pulmonary artery. Aortic valve opens when the left ventricle starts contracting. Blood is pumped from the left ventricle to the aorta through the open aortic valve.

 

Valve Diseases

The important factors for a valve to work without defect are- there shouldn’t be any structural deformities; they should be flexible in nature; proper opening and closing while blood passes through the heart. The valves should close tightly preventing the backflow of blood.

The major problems associated with valves are Regurgitation, Stenosis, and Artesia.

Regurgitation

In this condition, the valve doesn’t close properly. This causes a backflow of blood. When regurgitation of the mitral valve and tricuspid valve happens, blood leaks back into the atria from the ventricles. If regurgitation happens in aortic and pulmonary valves, the blood leaks back into ventricles. This leakage results in the overworking of the respective heart chambers. In the long run, it creates structural and functional changes in heart chambers. This affects the normal pumping of blood.

Stenosis

In this case, the opening of the valve gets narrowed and thus, the correct opening of the valve does not occur. Through this narrowed opening the heart has to pump harder. Only then will the blood pass through the narrowed valve. Since the heart has to exert more force to pump through this stiff valve, this also results in structural and functional changes in the chambers of the heart. Stenosis too affects the normal pumping of blood.

Artesia

This is a congenital problem. Here, the valve opening doesn’t develop during childhood. This defect blocks the passage of blood from atria to ventricle or from ventricle to the pulmonary artery or aorta.

There will be an atrial septal defect or ventricular septal defect in this case which will be present from birth. This creates another route for the blood to move through the heart. This too affects the heart’s ability to pump through the body.

Valve problems also occur due to age-related factors and illnesses like rheumatic fever and infective endocarditis.

 

Four Valves and Related Valve Problems

Tricuspid valve

Closes the right atrium which has deoxygenated blood from the entire body. When the valve opens, blood flows from the right atrium into the right ventricle. While blood gets pumped out of the right ventricle, the tricuspid valve prevents the backflow of blood from the ventricle to the atrium.

Valve problems related to the tricuspid valve include:

  • Tricuspid atresia
  • Tricuspid regurgitation
  • Tricuspid stenosis.

Pulmonary valve 

When it is opened, the blood from the right ventricle is pumped to the pulmonary artery. This artery carries blood to the lungs to get oxygenated. When closed, the backflow of blood to the right ventricle is prevented.

Valve problems related to this valve are

  • Pulmonary valve stenosis
  • Pulmonary valve regurgitation.

Mitral valve

When open, this valve allows the blood from the left atrium to reach the left ventricle. When closed, the oxygenated blood remains in the left atrium.

The valve problems associated with mitral valve are

  • Mitral valve prolapse
  • Mitral valve regurgitation
  • Mitral valve stenosis

Aortic Valve

The opening of this valve allows blood to flow into the aorta which carries blood to the entire body.

The valve problems associated with this valve are

  • Aortic regurgitation
  • Aortic stenosis

 

Causes of heart valve diseases

Calcification associated with aging

Calcium gets accumulated in heart valves, this hardens and thickens the valve. As a result, stenosis or narrowing of valve opening happens and blood flow is obstructed. Aortic valves are frequently affected by this condition. This forces the heart to work harder.

Degenerative valve disease

Due to the improper valve movements, the attachments of valves rupture and lead to leakage of the valve. This is mostly seen in the mitral valve.

Rheumatic fever

It is a group A streptococcal bacterial infection. It affects the leaflet tissue of heart valves thus, resulting in a stenotic heart valve.

Coronary artery disease

As a result of heart attack, the heart muscles get damaged and this, in turn, affects the function of valves. When the left ventricle gets enlarged after a heart attack, it affects the mitral valve. In this condition the mitral valve gets stretched, resulting in leakage.

Congenital abnormalities

The defects present from birth like malformed valves or the absence of heart valves can affect the flow of blood.

Bacterial endocarditis

This bacterial infection results in the damage and deformity of valves. Mostly seen in mitral valves, this results in a leaky valve or valve regurgitation.

 

Symptoms of Heart Valve Diseases

The symptoms of heart valve diseases include dizziness or fainting, irregularity in heartbeat, swollen ankles or feet, shortness of breath, fatigue, abnormal heart murmurs when observed with a stethoscope, etc.

 

Diagnosis of Heart Valve Diseases

The heart valve diseases can be diagnosed through X-rays, electrocardiography, coronary angiography, listening to heart murmurs, etc.

 

Treatment for Valve Diseases

Medical Therapy

The symptoms of heart valve diseases can be managed by medical therapies. But, in the long run, valves need to be surgically repaired or replaced.

Medical Therapies include administering drugs like

  • ACE inhibitors to lower blood pressure
  • Beta-blockers to slow heartbeat
  • Anti-arrhythmic drugs
  • Anticoagulants to prevent blood clot
  • Diuretics to remove excess body fluid
  • Drugs to dilate blood vessels

Surgical Treatment

Replacement

Transcatheter aortic valve replacement

In this procedure, a catheter is used to replace the heart valve instead of open-heart surgery. The new valve is inserted through a catheter and implanted inside the existing aortic valve. Usually, this is done in patients who cannot undergo open-heart surgery.

Open heart surgery for replacing the valve with metallic or bioprosthetic valve

Two categories of prosthetic heart valves are used in replacement. They are mechanical and bioprosthetic valves.

  • Mechanical Valves: These are usually made of carbon and titanium. They last long, but the downside of this option is that the patient will be on blood-thinning drugs. This is to prevent blood clots which disrupt the valve flaps from functioning. Mechanical valves rarely wear out.
  • Bioprosthetic Valves: Bioprosthetic heart valves are made from bovine or porcine pericardium or valves taken from human cadavers. This doesn’t have a long life span like the mechanical valves but causes fewer blood clots. Bioprosthetic valves require the use of anticoagulants for a lesser period. More research is to be done to transform this into a fool-proof option.

The choice of selection of the valve should be made depending on the patient’s lifestyle, age, and medical condition.

Valve Repair

Valve repair is always the most preferred choice among patients. Here, the tissues and structures of the valve are modified. It is done by the placement of the annuloplasty ring or band around the annulus of the existing valve. Annuloplasty ring is a cloth-covered device. It supports the existing valve and brings the flaps together. This reduces leakage across the valve. Other repair procedures are the correction of leaflets and chords of the heart valve. In mitral valve prolapse, this fixing can restore normal function.

 

References:

  1. Bateman, M. G., Quill, J. L., Hill, A. J., & Iaizzo, P. A. (2013). Heart Valves: From Design to Clinical Implantation. Springer US.
  2. Gross, L. & Kugel, M.A. (1931). Topographic Anatomy and Histology of the Human Heart. The American Journal of Pathology, 7(5), 445-474.
  3. Hinton, R.B. & Yutzey, K.E. (2011). Heart Valve Structure and Function in Development and Disease. Annual Review of Physiology, 73(1), 29-46.
  4. Wilcox, B.R., Cook, A.C., & Anderson, R.H. (2004). Surgical Anatomy of the Heart. Cambridge: Cambridge University Press.

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