Hrt Valve_4th Sem

SILIGURI INSTITUTE OF TECHNOLOGY Name:-Moina Ersad. B-Tech ,2nd Year ,4th Semester Department of Biomedical Engineering. Roll No.:-11931061009 Session:-2007-2008 Guide Teacher:-Sujan K.Samanta

Topic of Seminar:-

“ARTIFICIAL HEART VALVES”

HEART:Heart is a vital part of the human anatomy, as it functions as a pump to circulate blood throughout the body . It consists of four chambers , namely the right atrium ,the right ventricle ,the left atrium and the left ventricle.

By the pumping action of the heart, oxygenated blood is circulated throughout the body, and the deoxygenated blood is circulated back to the heart ,to regain the oxygen that was lost.

HEART VALVES:Heart valves are very important ,as they prevent the backflow of blood .This ensures the proper direction of blood flow throughout the circulatory system .Without these valves the heart would have to work much harder to push blood to the adjacent chambers.

There are four types of heart valves• Tricuspid valves • Pulmonary valves • Bicuspid or Mitral valves • Aortic valves

HEART VALVE PROBLEMS:Heart valves are prone to disease and malfunction ,and can be replaced by artificial heart valves .These complications and diseases of heart valves can prevent the proper flow of blood throughout the body. They are of two types:• Stenosis • Incompetence

• STENOSIS:-A stenotic heart valve prevents the valve from opening fully ,due to stiffened valve tissue .Hence there is more work required to push blood through the valve. • INCOMPETENCE:-Incompetent valves cause inefficient blood circulation by permitting backflow of blood in the heart.

Echocardiogram of aortic valve stenosis: calcified leaves arrowed

TREATMENT OPTIONS On a large scale, medication is the best alternative ,although in some cases defective valves have to be replaced by prosthetic valve, in order to make the patient lead a normal life. A lot of research work is being done by scientists and engineers to design a heart valve that can withstand millions if not billions of cardiac cycle.

Original photo of a replaced heart valve

TYPES OF PROSTHETIC HEART VALVES

There are two main types of Prosthetic heart valve designs:• Mechanical • Bioprosthetic The mechanical valves are excellent in terms of durability, but have a tendency to coagulate blood. Bioprosthetic valves are less durable and must be replaced periodically.

The operating principle of different types of prosthetic heart valves

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. • They emphasize on producing more central flow and reducing blood clots. • The common types of mechanical prosthetic heart valves are caged ball, tilting disc, bileaflet valve.

Different types of mechanical heart valves

Caged ball design:-

• The caged ball design is one of the early mechanical heart valves. • They use a small ball that is held in place by a welded metal cage. It limits the flow of fluids in a single direction.

But there are certain disadvantages of caged ball designs. • Caged ball designs completely block central flow, therefore the blood requires more energy to flow around the central ball. • The ball causes damage to blood cells due to collisions. • These damaged blood cells release clotting ingredients. As a result, the patients are required to take lifelong prescriptions of anticoagulants.

Tilting disc design:-

• This new class of prosthetic valves were introduced in the mid 1960s. • They used a tilting disc, that 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 two struts in such a way, as to close when the blood begins to move backward, and then reopens when the blood begins to travel forward.

A tilting disc heart valve

A 3-D image of tilting disc valve

There are certain advantages of tilting disc design over caged ball design:• They provide improved central flow while still preventing backward flow. • They reduce mechanical damage to blood cells. Hence there is a reduced chance of blood clotting and infection. The main disadvantage of the tilting disc design is:There is a tendency of the outlet struts to fracture, resulting from fatigue, due to repeated ramming of the struts by the disc.

Bileaflet valve:-

• In 1979 ,a new type of mechanical heart valve was introduced, known as the bileaflet valve. • It consists of two semicircular carbon leaflets that pivot on hinges. • The carbon leaflet exhibit high strength and excellent biocompatibility. • The leaflets swing open parallel to the direction of blood flow. • They constitute majority of the modern valve designs.

A bileaflet prosthetic valve

Bileaflet valve replacement

The main disadvantage of bileaflet valve is that, they do not close completely, which allows some backflow of blood. Since backflow is one of the properties of defective valves, so bileaflet valves are still not the ideal valves. The main advantage of these valves is that, they provide the closest approximation to central flow, normally achieved in a natural heart valve.

Bioprosthetic heart valves Bioprosthetic valves can be broken into two groups:• Human tissue valves • Animal tissue valves

Human tissue valve:-

Human tissue valves fall into two categories:Homograft:-It is a valve that is transplanted from a deceased person to a recipient. It suffers minimum problems of valve rejection, and hence do not require immunosuppressive therapy .They are more durable. Autograft:-They are taken from the same patient they are implanted into. The most common autograft procedure is the Ross procedure,

Animal tissue valves:The animal tissue valves are often referred to as heterograft or xenograft valves. These are the animal heart tissues which are often recovered from animals at the time of commercial processing. The most commonly used animal tissues are: • Porcine-valve tissue obtained from pig • Bovine-pericardial tissue obtained from cow.

A porcine valve

A Bovine valve

Heart valve replacement

Advantages of Bioprosthetic heart valve over mechanical heart valve

• The design of the bioprosthetic heart valve is closer to the design of natural valve. • The bioprosthetic valves do not require long term anticoagulants. • They have better haemodynamics. • They do not cause damage to blood cells • They do not suffer from many of the structural problems, experienced by the mechanical

Conclusion:When one of the valves of the heart becomes infected with disease, it can be replaced with one of several different types of prosthetic valves. The prosthetic valves must meet certain standards with regard to inertia, strength, elasticity and electrochemical properties. The replacement valve must also be durable as the human body is a harsh place for foreign objects, which can corrode or breakdown.

References:• Biomaterials by Sujata Bhatt • www.clevelandclinic.org • www.atsmedical.com • www.wikipedia.org • www.yeastinfectionadvisor.com