Prosthetic Heart Valves

What is a Prosthetic Heart Valve?

A prosthetic heart valve is an artificial device surgically implanted into the heart to replace a heart valve that has become damaged.

The human heart has four valves, the tricuspid, pulmonary, mitral and aortic. When any of the four heart valves malfunction, the affected valve is replaced with a prosthetic heart valve to replicate the normal functions.

In most cases, prosthetic heart valve replacement operation is done by open heart surgery. In some cases, the prosthetic valve can be replaced without opening the chest by techniques such as minimally invasive surgery or transcatheter valve replacement.

Some people are born with heart valve disease [congenital], while others acquire it later in life. Heart valve disease can cause regurgitation or backflow of blood. Stenosis of heart valve causes insufficient passage of blood through the heart chambers. Such conditions cannot be treated with medicines and surgery is the only option. Prosthetic heart valves are designed from either synthetic or bio materials.

What are the Different Types of Heart Valves?

During each heartbeat both of the atria contract first to pump blood into the ventricles. Then both ventricles contract to pump blood out of the heart into the arteries. These valves allow only unidirectional flow of blood between the atria and ventricles and also between the ventricles and the large arteries that take blood from the heart. These are:

The mitral valve - lies between the left atrium and the left ventricle. This is the most commonly affected valve for which prosthetic valve surgery is carried out.

The tricuspid valve - lies between the right atrium and the right ventricle. Damage to the tricuspid valve causes enlarged liver, abdominal swelling, swelling in the legs, and fatigue. The severity of the symptoms makes a doctor decide whether a prosthetic heart valve surgery is indicated or not.

The pulmonary valve - lies between the right ventricle and the pulmonary artery. The majority of pulmonary valve problems occur due to congenital heart disease. Stenosis of the valve leads to a volume overload and therefore to a dilation of the right ventricle.

The aortic valve - lies between the left ventricle and the aorta. Severe damage to the valve may lead to congestive heart failure necessitating a replacement with prosthetic valve.

What are the Symptoms of a Heart Valve Problem?

The symptoms depend on which heart valve is involved. Aortic and mitral valve problems are most common.

• Chest pain - mostly occurs when the aortic valve opening narrows down [aortic stenosis] to about one third the normal size. This leads to an insufficient amount of oxygenated blood being supplied to the body including the heart causing pain in the chest.
• Heart murmur - is an unusual heartbeat sound which can be heard by the doctor with a stethoscope. Location of murmur helps to pinpoint the diseased valve.
• Palpitation (rapid and irregular heartbeats) - occurs mostly in aortic regurgitation when there is back flow of oxygenated blood to the left ventricle. Associated symptoms include dizziness, shortness of breath, sweating, headaches, and chest pain.
• Cardiac arrhythmias - mostly occur in aortic regurgitation, and mitral stenosis. A heart rate that is above 100 beats per minute in adults is called tachycardia and a heart rate that is below 60 beats per minute is called bradycardia.
• Shortness of breath during exertion [exertional dyspnea] - occurs in cases of aortic regurgitation, mitral stenosis, mitral regurgitation, and congenital heart valve problems
• Coughing up of blood - is a common symptom of mitral stenosis.
• Sudden severe shortness of breath during the middle of the night - occurs in mitral stenosis.
• Clots in left atrium - occurs in cases of mitral stenosis. These clots can travel through the blood vessels and cause damage to other organs.
• Breathlessness when lying down [orthopnea] - is characteristic of aortic regurgitation.
• Fatigue, weakness, or inability to maintain regular activity level- is mostly due to pulmonary or pulmonic valve problems.

• Fainting [syncope] - is common symptom in aortic stenosis, and pulmonic valve problems.
• Cyanosis or bluish discoloration of skin - occurs mostly in congenital heart problems due to accumulation of deoxygenated blood in the body.
• Swelling in ankles, feet, legs, abdomen, and veins in the neck - occurs when the pulmonic valve is affected.

What are the Types of Prosthetic Heart Valves?

The two types of heart valves are:

• Mechanical heart valves - which are made of a strong material such as titanium or carbon that make them incredibly strong and durable. There are three major types of mechanical valves - caged-ball, tilting-disk and bileaflet valve with many modifications on these designs.
• Tissue [bioprosthetic] valves -include homograft / allografts [a graft of tissue between individuals of the same species but of different genotypes] or xenografts [tissue that is removed from one species and grafted onto another species]. Usually bovine or porcine tissue is used. These valves are also known as bioengineered valves.

How does a Prosthetic Heart Valve Work?

Valves are integral to the normal functioning of the human heart. Each valve has a tissue flap that opens and closes with every heartbeat. These are responsible for the unidirectional blood flow from one heart chamber to another.

During a heart valve replacement procedure, the diseased heart valve is replaced with a prosthetic or artificial heart valve. This artificial valve is designed to function like a normal natural healthy heart valve. The prosthetic heart valves open and close with each heartbeat, permitting proper blood flow through the heart.

The first prosthetic heart valve was the caged-ball, which houses a silicone elastomer ball in a metal cage. When blood pressure in the chamber of the heart exceeds the pressure on the outside, the ball is pushed against the cage and allows blood to flow. When the heart's contraction is completed, the pressure inside the chamber is lower than the outside, so the ball moves back against the base of the valve forming a seal.

Bileaflet valves have two semicircular leaflets which open and close creating one central and two peripheral orifices. These are the most commonly implanted type of mechanical heart valves worldwide.

What are the Advantages and Disadvantages of Prosthetic Heart Valves?

Advantages:

The mechanical prosthetic heart valves are very durable and guarantee 20-30 years of functioning in ideal conditions. The coating with pyrolytic carbon in mechanical valves also decreases the chance of blood clotting on the valve surface.

Patients who have replaced their damaged valves with tissue heart valvesdo not need to take lifelong blood thinning therapy.

Replacing a defective valve with a prosthetic valve helps a patient to lead a much longer and better quality of life.

Disadvantages:

Tissue prosthetic heart valves have limited durability of only 10 to 20 years. Many patients require a repeat operation in their life time.

Failures in mechanical heart valves occur in about 10 to 15 percent of cases. Though structural damage is rare but some of them might still need to be replaced because of infections and blood clots. The clots can jam the mechanical valve in an open or closed position causing stenosis, insufficiency or a combination of both. Some clots can come loose and travel from the prosthetic valve to the arteries that supply the heart (coronary arteries) or to the brain (carotid arteries) causing a stroke or a heart attack. There is a higher rate of thrombotic and thromboembolic complications with mechanical heart valves.

The main disadvantage with mechanical prosthetic heart valves is that patients will have to take anti coagulants [blood thinners] for the rest of their lives to prevent the formation of dangerous blood clots. Also, frequent blood tests have to be conducted to monitor the thinning of blood as the thinned out blood may lead to serious bleeding complications.

What are the Complications of Prosthetic Heart Valves?

Early complications include bleeding and inflammation leading to a pericardial effusion, atrial arrhythmias, chest pain, cardiac tamponade [compression of the heart due to fluid buildup around the heart].

Other complications include prosthesis patient mismatch, thromboembolism, structural failure of modern prosthetic heart valves, and hemolytic anemia, prosthetic heart valve regurgitation, prosthetic valve endocarditis and prosthetic valve-related hemolysis.

Effects from the surgery itself include bleeding, infection, and risks associated with anesthesia. The risk of death from the surgery is about 3% to 9%. The intensity of complications depends on age, heart health, and other medical problems. Blood clots on or around the prosthetic valve can also occur.

References:

1. Heart Valve Disease - (https://www.nhlbi.nih.gov/health/health-topics/topics/hvd/treatment)
2. Prosthetic Heart Valves - (http://www.nejm.org/doi/full/10.1056/NEJM199608083350607)
3. Choice of heart valve prosthesis - (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1767148/)
4. Symptoms of Heart Valve Problems - (http://www.heart.org/HEARTORG/Conditions/More/HeartValveProblemsandDisease/Symptoms-of-Heart-Valve-Problems_UCM_450832_Article.jsp#.Wilvy0rXbIU)
5. Heart Valve Disease and Treatment - (http://www.montefiore.org/types-of-heart-valves)

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