35 '09 Alive!: When A Heart Valve Fails.

HOW DO HEART VALVES WORK?

The valves of the heart are located within the chambers of the heart and are critical to the proper flow of blood through the heart. All of the valves, when functioning normally, act as one-way valves, allowing blood to flow either from one chamber to another, or allowing blood to flow out of the heart, in only one direction. The valves control the flow of blood through the heart by opening and closing during the contractions of the heart. The opening and closing functions of the valves are controlled by pressure differences generated within the heart, as well as some muscles located within the heart.

Your heart has four chambers and four valves that regulate blood flow:

Mitral valve:
The mitral valve controls the flow of oxygen-rich blood from the left atrium to the left ventricle

Tricuspid valve:
The tricuspid valve controls the flow of oxygen-poor blood from the right atrium to the right ventricle

Aortic valve:
The aortic valve controls flow of oxygen-rich blood from the left ventricle to the body

Pulmonary valve:
The pulmonary valve controls flow of oxygen-poor blood from the right ventricle to the lungs

Heart Valves @ Work

Blood enters the heart through the right atrium, which then contracts, sending it to the right ventricle. The right ventricle contracts and propels the blood into the blood vessels of the lungs.
Full of oxygen, the blood leaves the lungs and re-enters the heart through the pulmonary veins, which empty into the left atrium. The left atrium contracts and thrusts the blood into the left ventricle, which contracts, sending the blood to the body and brain via the aorta and its branches.

During each heartbeat, valves open and close in a complex sequence that ensures efficient forward movement of blood.

The tricuspid and mitral valves open to allow blood to flow into the ventricles from the atria. During this time, the pulmonic and aortic valves are closed preventing leakage back into the ventricles of the blood ejected during the previous beat.

As the newly-filled ventricles contract, the pulmonic and aortic valves open, enabling blood to leave the heart. During this time, the mitral and tricuspid valves are closed preventing blood from flowing back into the atria.

These valves are essential to the efficient movement of blood throughout the heart and into the body.

Each valve has a set of flaps known as leaflets or cusps. When the valves are in good working order, the flaps open and close completely. If the valves are not working properly, the heart has to work harder than normal to pump blood.

See how the Heart Valves work at -
http://video.about.com/heartdisease/How-the-Valves-Work.htm

WHY WILL HEART VALVES FAIL? HOW WILL THEY NOT WORK?

What Are the Types of Valve Disease?

Valvular stenosis - This occurs when a valve opening is smaller than normal due to stiff or fused leaflets. The narrowed opening may make the heart work very hard to pump blood through it. This can lead to heart failure and other symptoms (see below). All four valves can be stenotic (hardened, restricting blood flow); the conditions are called tricuspid stenosis, pulmonic stenosis, mitral stenosis or aortic stenosis.

Valvular insufficiency - Also called regurgitation, incompetence or "leaky valve", this occurs when a valve does not close tightly. If the valves do not seal, some blood will leak backwards across the valve. As the leak worsens, the heart has to work harder to make up for the leaky valve, and less blood may flow to the rest of the body. Depending on which valve is affected, the conditioned is called tricuspid regurgitation, pulmonary regurgitation, mitral regurgitation or aortic regurgitation.

What Causes Valvular Heart Disease?

Valve disease can develop before birth (congenital) or can be acquired sometime during one's lifetime. Sometimes the cause of valve disease is unknown.

Congenital valve disease. Most often affects the aortic or pulmonic valve. Valves may be the wrong size, have malformed leaflets, or have leaflets that are not attached to the annulus correctly.

Bicuspid aortic valve disease is a congenital valve disease that affects the aortic valve. Instead of the normal three leaflets or cusps, the bicuspid aortic valve has only two. Without the third leaflet, the valve may be stiff (unable to open or close properly) or leaky (not able close tightly).
Acquired valve disease. This includes problems that develop with valves that were once normal. These may involve changes in the structure or your valve due to a variety of diseases or infections, including rheumatic fever or endocarditis.

Rheumatic fever is caused by an untreated bacterial infection (usually strep. throat). Luckily, the introduction of antibiotics to treat this infection has dramatically reduced the numbers of this infection. The initial infection usually occurs in children, but the heart problems associated with the infection may not be seen until 20-40 years later. At that time, the heart valves become inflamed, the leaflets stick together and become scarred, rigid, thickened and shortened. This leads to mitral regurgitation.

Endocarditis occurs when germs, especially bacteria, enter the bloodstream and attack the heart valves, causing growths and holes in the valves and scarring. This can lead to leaky valves. The germs that cause endocarditis enter the blood during dental procedures, surgery, IV drug use, or with severe infections. People with valve disease (except mitral valve prolapse without thickening or regurgitation/leaking) are at increased risk for developing this life-threatening infection.

There are many changes that can occur to the valves of the heart. The chordae tendinea or papillary muscles can stretch or tear; the annulus of the valve can dilate (become wide); or the valve leaflets can become fibrotic (stiff) and calcified.

Mitral valve prolapse (MVP) is a very common condition, affecting 1 to 2 percent of the population. MVP causes the leaflets of the mitral valve to flop back into the left atrium during the heart's contraction. MVP also causes the tissues of the valve to become abnormal and stretchy, causing the valve to leak. The condition rarely causes symptoms and usually doesn't require treatment.

Other causes of valve disease include: coronary artery disease, heart attack, cardiomyopathy (heart muscle disease), syphilis (a sexually transmitted disease), hypertension, aortic aneurysms, and connective tissue diseases. Less common causes of valve disease include tumors, some types of drugs and radiation.

What Are the Symptoms of Valve Disease?

- Shortness of breath and/or difficulty catching your breath.
- Weakness or dizziness.
- Discomfort in your chest.
- Palpitations. (This may feel like a rapid heart rhythm, irregular heartbeat, skipped beats or a flip-flop feeling in your chest.)
- Swelling of your ankles, feet or abdomen. (This is called edema. Swelling may occur in your belly, which may cause you to feel bloated.)
- Rapid weight gain. (A weight gain of two or three pounds in one day is possible.)

Symptoms do not always relate to the seriousness of your valve disease. You may have no symptoms at all and have severe valve disease, requiring prompt treatment. Or, as with mitral valve prolapse, you may have severe symptoms, yet tests may show your valve leak is not significant.

How Are Valve Diseases Diagnosed?

Your heart doctor can tell if you have valve disease by talking to you about your symptoms, performing a physical exam, and giving you other tests.

During a physical exam, your doctor will listen to your heart to hear the sounds the heart makes as the valves open and close. A murmur is a swishing sound made by blood flowing through a stenotic or leaky valve. Your doctor can also tell if your heart is enlarged or if your heart rhythm is irregular.

The doctor will listen to your lungs to hear if you are retaining fluid in your lungs, which shows your heart is not able to pump as well as it should.

By examining your body, the doctor can find clues about your circulation and the functioning of your other organs.

After the physical exam, the doctor may order diagnostic tests. These may include:
Echocardiography
Transesophageal echocardiography
Cardiac catheterization (also called an angiogram)
Radionuclide scans
Magnetic resonance imaging (MRI)

By looking at the results, repeated over time, your doctor can also see the progress of your valve disease. This will help him or her make decisions about your treatment.

How Is Heart Valve Disease Treated?

Treatment for heart valve disease depends on the type and severity of valve disease. There are three goals of treatment for heart valve disease: protecting your valve from further damage; lessening symptoms; and repairing or replacing valves.

Protecting your valve from further damage.

If you have valve disease, you are at risk for developing endocarditis, a serious condition. People who have mitral valve prolapse without thickening or regurgitation/leaking are not at risk of developing endocarditis.

You are still at risk for endocarditis, even if your valve is repaired or replaced through surgery. To protect yourself:

Tell your doctors and dentist you have valve disease.
Call your doctor if you have symptoms of an infection
Take good care of your teeth and gums to prevent infections. See your dentist regularly.
Take antibiotics before you undergo any procedure that may cause bleeding, such as any dental work (even a basic teeth cleaning), invasive tests (any test that may involve blood or bleeding), and most major or minor surgery.

Medications.

You may be prescribed medications to treat your symptoms and to lessen the chance of further valve damage. Some medications may be stopped after you have had valve surgery to correct your problem. Other medications may need to be taken all your life. Medications may include:

Diuretics ("water pills") - Remove extra fluid from the tissues and bloodstream; lessen the symptoms of heart failure
Antiarrhythmic medications - Control the heart's rhythm
Vasodilators - Lessen the heart's work. Also encourages blood to flow in a forward direction, rather than backwards through a leaky valve.
ACE inhibitors - A type of vasodilator used to treat high blood pressure and heart failure
Beta blockers - Treat high blood pressure and lessen the heart's work by helping the heart beat slower and less forcefully. Used to decrease palpitations in some patients.
Anticoagulants ("blood thinners") - Prolong the clotting time of your blood, if you are at risk for developing blood clots on your heart valve.

Surgery and Other Procedures.

The diagnostic tests your heart doctor orders help to identify the location, type, and extent of your valve disease. The results of these tests, the structure of your heart, your age, and your lifestyle will help your cardiologist (heart doctor), surgeon, and you decide what type of procedure will be best for you.

Surgical options include heart valve repair or replacement. Valves can be repaired or replaced with traditional heart valve surgery or a minimally invasive heart valve surgical procedure. Heart valves may also be repaired by other procedures such as percutaneous balloon valvotomy.

TYPES OF VALVE IMPLANTS

The two main prosthetic valve designs include mechanical and bioprosthetic heart valves.

Mechanical Heart Valves

Evolution of Mechanical Heart Valves

The first mechanical prosthetic heart valve was implanted in 1952. Over the years, 30 different mechanical designs have originated worldwide. These valves have progressed from simple caged ball valves, to modern bileaflet valves. Heart valves are designed to fit the peculiar requirements of blood flow through the specific chambers of the heart, with emphasis on producing more central flow and reducing blood clots.

The caged ball design is one of the early mechanical heart valves, that uses a small ball that is held in place by a welded metal cage. The ball in cage design was modeled after ball valves used in industry to limit the flow of fluids to a single direction. Natural heart valves allow blood to flow straight through the center of the valve. This property is known as central flow, which keeps the amount of work done by the heart to a minimum. With non-central flow, the heart must work harder to compensate for the momentum lost to the change of direction of the fluid. Caged-ball valves completely block central flow, therefore the blood requires more energy to flow around the central ball. In addition, the ball is notorious for causing damage to blood cells due to collisions. Damaged blood cells release blood clotting ingredients, hence the patients are required to take lifelong prescriptions of anticoagulants.

For a decade and a half, the caged ball valve remained the best design. In the mid-1960s, a new class of prosthetic valves were designed that used a tilting disc to better mimic the natural patterns of blood flow. The tilting-disc valves have a polymer disc held in place by two welded struts. The disc floats between the two struts in such a way, as to close when the blood begins to travel backward and then reopens when blood begins to travel forward again. The tilting-disc valves are vastly superior to the ball-cage design. The titling-disc valves open at an angle of 60° and close shut completely at a rate of 70 times/minute. This tilting pattern provides improved central flow while still preventing backflow. The tilting-disc valves reduce mechanical damage to blood cells. This improved flow pattern reduced blood clotting and infection. However, the only problem with this design is its tendency for the outlet struts to fracture as a result of fatigue from the repeated ramming of the struts by the disc.

In 1979, a new mechanical heart valve was introduced. These valves were known as bileaflet valves, and consisted of two semicircular leaflets that pivot on hinges. The carbon leaflets exhibit high strength and excellent biocompatibility. The leaflets swing open completely, parallel to the direction of the blood flow. They do not close completely, which allows some backflow. Since backflow is one of the properties of defective valves, the bileaflet valves are still not ideal valves. The bileaflet valve constitutes the majority of modern valve designs. These valves are distinguished mainly for providing the closest approximation to central flow achieved in a natural heart valve.

Materials

Current research has been able to produce materials that do not cause clotting in the blood stream. However, they have yet to design an entire valve that will not induce coagulation.
Most commonly used materials include:
- stainless steel alloys
- molybdenum alloys
- pyrolitic carbon for the valve housings and leaflets
- silicone, teflon®
- polyester (Dacron®) for sewing rings

A new generation of mechanical valves made of materials with improved blood contact properties, better wear characteristics and resistance to infection are under development.

Advantages

The main advantages of mechanical valves are their high durability. Mechanical heart valves are placed in young patients because they typically last for the lifetime of the patient.

Disadvantages

The main problem with all mechanical valves is the increased risk of blood clotting. When blood clots of any kind occur in the heart, there is a high probability of a heart attack or stroke. As a result, to prevent blood clots, mechanical valve recipients must take anti-coagulant drugs (sodium warfarin) chronically, which effectively makes them borderline hemophiliacs. The anti-coagulant used causes birth defects in the first trimester of fetal development, rendering mechanical valves unsuitable for women of child-bearing age. Mechanical valves are suitable for people who do not want additional valve replacement surgery in the future.

The Future of Mechanical Heart Valves

The new age tools that are being used to improve mechanical valve design include accelerated wear testing, advanced blood contact property testing, computer assisted design and manufacturing, coatings to reduce the chance of infection and improve healing and advanced polymer chemistry to develop the next generation of medical materials.

Bioprothestic/Prothestic tissue valves

Prosthetic tissue valves can be broken into two groups: human tissue valves, and animal tissue valves. Both types are often referred to as bioprosthetic valves, which hold many advantages over mechanical valves. The design of bioprosthetic valves are closer to the design of the natural valve. Bioprosthetic valves do not require long-term anticoagulats, have better hemodynamics, do not cause damage to blood cells, and do not suffer from many of the structural problems experienced by the mechanical heart valves.

Human Tissue Valves

Human tissue valves fall into two categories: Homografts, which are valves that are transplanted from another human being, and Autografts, which are valves that are transplanted from one position to another within the same person.

A homograft is a valve that is transplanted from a deceased person to a recipient. A recipient has minimal problems with valve rejection and they do not require immunosuppressive therapy. A homograft that has been donated must be cryopreserved in liquid nitrogen until it is needed. In cases where the valve implants fit the dimensions of the patient correctly, homografts tend to have good hemodynamics and good durability. However, it is not clear whether homografts have better hemodynamics or durability than animal tissue valves.

Autografts are valves taken from the same patient that they are implanted into. The most common autograft procedure is the Ross procedure, which is used in patients with diseased aortic valves. The dysfunctional aortic valve is removed and the patient's pulmonic valve is then transplanted to the aortic position. A homograft pulmonic valve is usually used to replace the patient’s pulmonic valve. The Ross procedure allows the patient the advantage of receiving a living valve in the aortic position. The long term survival and freedom from complications for patients with aortic valve disease are better with the Ross Procedure than any other type of valve replacement. After 20 years, only 15% of patients require additional valve procedures. In cases where a human pulmonary artery homograft is used to replace the patients’ pulmonary valve, freedom from failure has been 94% after 5 years time, and 83% at 20 years. The tissues of the patients’ pulmonary valve have not shown a tendency to calcify, degenerate, perforate, or develop leakage.

The Ross procedure requires a high level of technical skill on the part of the surgeon. The pulmonic valve and the pulmonary homograft must be sculpted to fit the aortic root. Many patients have small amounts of aortic regurgitation, which in some cases is severe enough to merit a second operation for valve replacement. Other possible complications could include stenosis, right-sided endocarditis, as well as the usual complications of valve replacement.

Animal Tissue Valves

Animal tissue valves are often referred to as heterograft or xenograft valves. These valves are most often heart tissues recovered from animals at the time of commercial meat processing. The leaflet valve tissue of the animals is inspected, and the highest quality leaflet tissues are then preserved. They are then stiffened by a tanning solution, most often glutaraldehyde. The most commonly used animal tissues are: porcine, which is valve tissue from a pig, and bovine pericardial tissue, which is from a cow.

In Porcine valves, the valve tissue is sewn to a metal wire stent, often made from a cobalt-nickel alloy. The wire is bent to form three U-shaped prongs. A Dacron cloth sewing skirt is attached to the base of the wire stent, and then the stents themselves are also covered with cloth. Porcine valves have good durability and usually last for ten to fifteen years.

Bovine pericardial valves are similar to porcine valves in design. The major difference is the location of the small metal cylinder which joins the ends of the wire stents together. In the case of pericardial valves, the metal cylinder is located in the middle of one of the stent post loops. Pericardial valves have excellent hemodynamics and have durability equal to that of standard porcine valves after 10 years.

Both the porcine and bovine pericardial valves are stented valves. The metal stent in these valves takes up room which could be available for blood flow. Stentless valves are made by removing the entire aortic root and adjacent aorta as a block, usually from a pig. The coronary arteries are tied off, and the entire section is trimmed and then implanted into the patient. The St. Jude Toronto Stentless Porcine Valve (SPV) is one such valve. It appears to have excellent hemodynamics, and a significant decrease in the thickness of the heart has been observed after the valve is implanted. However, the valve is extremely difficult to implant, and it is still too new to have any valid data accounting for durability.

The most common cause of bioprosthesis failure is stiffening of the tissue due to the build up calcium. Calcification can cause a restriction of blood flow through the valve (stenosis) or cause tears in the valve leaflets. Since younger patients have a greater calcium metabolism, bioprostheses tend to last best in senior citizens. Once a bioprosthesis is implanted, the valve itself does not require any type of anti-coagulant drugs. Its degeneration is simply a gradual process, as it grows with the body.

The future for replacement heart valves lies in tissue engineering. The most ideal replacement would be formed from the patient's tissue, and tailored to the right shape and dimensions. Researchers have transplanted specifically tailored valves into sheep. The valves are made by growing tissue from the artery of a lamb on a matrix of the correct dimensions in an artificial culture medium.

DO ALL VALVE IMPLANTS WORK THE SAME WAY? WHAT ARE THEIR ADVANTAGES AND LIMITATIONS?

ARTIFICIAL HEART VALVES are very difficult to make properly because of the tremendous performance requirements associated with such a crucial replacement. The materials must be extremely durable, the valve must resist extensive wear, it must be completely impervious when sealed, it should be easy to implant surgically, and there should be little or no tendency of blood to clot on the valve.

Things to expect before the operation:

1. There will be a heart-lung machine, pumping in oxygenated blood around the body
2. You will receive an intravenous (IV) line in your arm or hand. This will enable your doctor to administer medications and fluids

What to expect during and after the operation:

1. You will be placed in the ICU after the operation so that you can be closely monitored
2. A tube will still be in position upon waking up
3. A monitor will show your heart rate, heart rhythm, blood pressure and other special waves, essential for nurses to monitor closely.
4. You will take about 6 to 8 weeks to get back to your daily routine upon discharge

Complications of operation:

Anesthesia - Reactions to medications, Problems breathing
Surgery - Bleeding, Infection
Cardiac surgery - Death, Stroke, Heart attack, Arrhythmia, Kidney failure, Temporary postoperative confusion due to the heart-lung machine

FYI