artificial heart

ARTIFICIAL HEART A PROMISING APPROACH IN ARTIFICIAL ORGANS

Liliana Agostinho, 65109 and Joana Paulo, 72455

Master in Biomedical Engineering, 4th

year, 2nd

semester 2012

ABSTRACT

The emerging need of finding solutions on the medicine field appeals for high

technology intervention. The artificial organs’ development makes use of that

technology, not only using biomechanical techniques but also, and more recently,

cellular and tissue engineering allied to nanotechnology, to improve biocompability.

This paper makes an overview about what has been done in the field and focus the

particular case of the heart as an artificial organ, the different equipment and a future

perspective.

I. INTRODUCTION

One of the greatest advancements in the

world of medicine has been the ability to

create artificial organs that are able to restore

the proper function of a patient’s body. By

definition, an artificial organ is “a man – made

device that is implanted into the human body to

replace one or many functions of a natural

organ, which usually are related to life support”.

The main reasons for developing these devices

include:

o Life support to prevent imminent death

while awaiting a transplant;

o Dramatic improvement of the patient's

ability for self – care;

o Improvement of the patient's ability to

interact socially;

o Esthetic restoration after cancer surgery or

accident. [1,2]

The first case is the most critical and the one

that provides greater challenges for medical

and engineer community. Nowadays, the

average life expectancy is high due to better

healthcare, fact coupled with shortage of

organ donors, so organ assistance and

substitution devices will play a larger role in

managing patients with end-stage disease by

providing a bridge to recovery or a

transplant. For example, in the U.S. alone, the

annual need for organ replacement therapies

increases by about 10 percent each year.

The first approaches to artificial organs

only used synthetic components; however,

we can now talk in “biohybrid” organs, which

combine synthetic and biologic components,

often incorporating multiple technologies

involving sensors, new biomaterials, and

innovative delivery systems. [3]

The history of artificial organs started in

1885, when Frey & Gruber build and use the

first artificial heart–lung apparatus for organ

perfusion studies. Their device relies on a

thin film of blood and included heating and

cooling chambers, manometers, and

sampling outlets, which permits monitoring

of temperature, pressure, and blood gases

during perfusion. [4] Since that time, little

steps were taken towards the current

variability available.

The most obvious example may be the

dialysis machine, which although it implies a

continuous power supply, it completely

replaces the kidney’s function. There are

already other artificial options for the brain,

ear, eye, heart, limbs, liver, lungs, pancreas,

bladder, ovaries, uterus and trachea.

There’s a huge expectation that artificial

organs would be superior to ordinary donor

organs in several ways. They can be made to

ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455

2

order more quickly than a donor organ can

often be found; in a regenerative medicine

domain, it’s possible to construct an organ

being grown from a patient's own cells, so

there’s no need for immunosuppressant

drugs to prevent rejection.

II. STATE OF THE ART

The development of an artificial

implantable pancreas for treatment of diabetes

occurs since 1998 and is based on three

fundamental components: a blood glucose

monitor, an insulin pump and a control system.

The goals of this device are the prevention or

delay of chronic complications of diabetes, as

well as less patient inconvenience and

discomfort than with multiple glucose self-

tests and insulin injection. [5] The glucose

sensor consists on an immobilized enzyme and

an interface to an electrochemical transducer.

The main problem to overcome is the

progressive loss of function and lack of

reliability of the sensor, caused by tissue

reactions, such as inflammation, fibrosis and

loss of vasculature, harming time precision. [6]

Now there are two available models for

glucose sensors, MiniMed CGMS and

GlucoWatch. [7] The pump itself is placed

internally and injects continuously insulin on

peritoneal cavity.

According to a CNN publication (March

2012), this device is currently on a trial phase

and getting good results. [8]

Another type of approach is the

bioengineering one. A tissue containing islets

of Langerhans is implanted, which would

secrete the amount of insulin, amylin and

glucanon needed and deficient because of the

islets and beta cells destroyed by the disease.

They can be cells collected from animals or

designed from stem cells, and they are

encapsulated to block the immune response

and eliminate the requirement of

immunosuppressive drugs. [9]

Microencapsulation techniques are being

improved for providing an effective long-term

treatment or cure of type 1 diabetes. [10, 11]

Figure 1: The Bioartificial Pancreas using Islet Sheet technology.

On July 2011, in Sweden, an artificial

trachea, fully synthetic, tissue – engineered,

was successfully transplanted into a late –

stage tracheal cancer patient. The organ was

created entirely in the lab, using a scaffold

built out of a porous polymer, and tissue

grown from the patient's own stem cells

inside a bioreactor designed to protect the

organ and promote cell growth. [12]

Figure 2: Artificial trachea after two days of cell growth, just

before being implanted into the patient.

The first artificial organ for substituting

liver function was the Extracorporeal Liver

Assist Device (ELAD®), a bedside system that

treats blood plasma, metabolizing toxins and

synthesizing proteins just like a real liver

does. This device is used to extend patients’

lives until a liver transplant becomes

available, and it’s being explored if it can

relieve the burden on the patient’s liver

enough so that it can regenerate itself. [13]

On October 2006, it was noticed the world’s

first bioartificial liver has been grown from

stem cells by British scientists. The result liver

was the size of a coin but the same technique


3

can be employed to grow full-size livers.

Fifteen years from that time, it was predicted

these livers can be implanted into patients. [14,

15]

HepaLife, a company in Boston, announced

on 2008 the latest positive results of tests of its

PICM-19 cells inside the bioreactor that would,

if it becomes a real product, function as an

external liver. This device reduces levels of

toxic ammonia by 75% in fewer than 24 hours. [16]

Figure 3: HepaLife’s device structure.

III. HEART

11.. AAnnaattoommyy aanndd PPhhyyssiioollooggyy

The heart is a muscular organ, located on

the chest, which pumps the blood

continuously around the body through the

cardiac cycle. Its mass is between 250 and

350 grams and it is about the size of a fist. It

is surrounded by the lungs and protected by

the ribs and sternum. It’s constituted by a

contractile mass, called the myocardium,

coated inside by a thin membrane, the

endocardium, and outside by a double –

walled sac, the pericardium.

It is divided by the interatrioventricular

septum in two functionally separate and

anatomically distinct units, right and left: on

the first, only circulates venous blood returned

from the peripheral organs; on the second

circulates arterial blood, arriving from the

lungs, where it has been oxygenated.

Each half can be then cloven in two

chambers, the atrium and the ventricle. The

ventricles are separated from the atria by

atrioventricular (AV) holes, where are placed

valves that avoid blood reflux. There are the

mitral valve and tricuspid valve, on the left

and right side, respectively. These are

included on the blood pathway through the

heart, together with the aortic and pulmonary

valves.

Figure 4: Anterior view of the human heart.

The cardiac cycle has two phases: systemic

circulation, which begins at a contraction of

the left ventricle, pumping the blood out to the

body through the aorta, and ends when it

returns to the heart (right atrium) via superior

and inferior vena cava; pulmonary circulation,

starting on the right ventricle, then the blood

flows to the lungs where many gas exchange

occurs, and it arrives through the pulmonary

veins to the heart again (left atrium).

22.. PPaatthhoollooggyy

For the heart to fulfill its demanding task,

apart from a proper blood supply, it needs a

good functioning of the heart muscle. The

cardiac insufficiency (weakness of the heart

muscle) designates a disease in which the

heart muscle is weakened to such an extent

that it is no longer capable of pumping the

blood sufficiently powerful or adequately fast

through the blood vessels. In such a case, part

of the blood accumulates upstream of the


4

heart, and we refer to it as a cardiac

insufficiency or a heart weakness. The cause

for a cardiac insufficiency is to be found in an

acute or gradual injury of the heart muscle due

to, among others:

• cardiovascular disease;

• heart attack;

• high blood pressure;

• heart diseases that directly attack the

heart muscle or the cardiac valves.

If the symptoms occur all of a sudden and

rather quickly, we refer to it as an acute

cardiac insufficiency. The chronic cardiac

insufficiency, in contrast, often develops

slowly and gradually, in most cases over a

period of several months or years. [17]

The weak heart muscle causes the patients

to feel symptoms that result from the fact

that the heart is no longer capable of

providing a sufficient blood supply for the

body and blood accumulates upstream of the

heart. Early symptoms of a cardiac

insufficiency are:

• reduced physical fitness;

• shortness of breath during hard physical

activity, when climbing stairs or

exercising;

• water retention (edema) in ankles and

back of the foot.

In the further course of the disease the water

retention may also affect other organs

eventually resulting in a weight gain. In an

advanced case of cardiac insufficiency the

patient will feel breathlessness also under

slight physical stress or even when at rest.

We distinguish between different stages of

cardiac insufficiency: [9]

• low-level with the symptoms occurring

only under hardest physical stress;

• high-level with symptoms such as

shortness of breath already in a state of

rest;

The necessary treatment is determined by

the stage of the cardiac insufficiency.

IV. EVOLUTION: FROM VALVES TO TOTAL

ARTIFICIAL HEART

11.. HHiissttoorryy aanndd AAddvvaanncceess ooff AArrttiiffiicciiaall HHeeaarrtt VVaallvveess

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.

The caged ball design is one of the early

mechanical heart valves that use 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 avoid backflow.

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 due 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 may cause damage to blood

cells due to collision. Damaged blood cells

release blood-clotting ingredients; hence the

patients are required to take lifelong

prescriptions of anticoagulants. [18]

For a decade and a half, the caged ball valve

was the best artificial valve design. In the mid-

1960s, new classes 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


5

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 was its tendency for the outlet

struts to fracture as a result of fatigue from the

repeated ramming of the struts by the disc.

Figure 5: Caged ball valves. (a) Hufnagel–Lucite valve, (b) Starr–Edwards, (c) Smeloff–Cutter, (d) McGovern–Cronie, (e) DeBakey–Surgitool and (f) Cross–Jones.

Bileaflet valves were introduced in 1979.

The leaflets swing open completely, parallel

to the direction of the blood flow. The

bileaflet valves were 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. [19]

Figure 6: Bileaflet valve models. (a) St. Jude Medical, (b) Carbomedics and (c) Duramedics.

Biological tissue valves are made from

porcine aortic valves or fabricated using

bovine pericardial tissue and suitably treated

with gluteraldehyde to preserve them and to

remove antigenic proteins. Clinical

experiences with different tissue valve

designs have increasingly indicated time-

dependent (5 to 7 year) structural changes

such as calcification and leaflet wear, leading

to valve failure. Therefore tissue valves are

rarely used in children and young adults at

present. [18, 19] On the other hand, mechanical

valves made with high strength

biocompatible material are durable and have

long-term functional capability. However,

mechanical valves are subject to thrombus

deposition and subsequent complications

resulting from emboli, and so patients with

implanted mechanical valves need to be on

long-term anticoagulant therapy. Currently,

mechanical valves are preferred except in

elderly patients or those who cannot be put

under anticoagulant therapy, like women

who may still wish to bear children, or

hemolytic patients.

22.. MMeecchhaanniiccaall HHeeaarrtt VVaallvvee

Prosthetic Heart Valves are fabricated of

different biomaterials. Biomaterials 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. Some

of these biomaterials are alumina, titanium,

carbon, polyester and polyurethane.

The mechanical properties of these

biomaterials involve how a material responds

to the application of a force. The three

fundamental types of forces that can be

applied are stretching (tension), bending, or

twisting. Materials respond to the forces by

deforming (changing shape). An elastic

response is reversible, while an inelastic

response is irreversible. In the elastic region,

an elastic modulus relates the relative

deformation a material undergoes to the

stress that is applied. The transition between

elastic deformation and failure occurs at the

yield point (or stress) of the material. In

designing a component with the material, an

inelastic response is considered failure.

Failure can be plastic deformation or ductile

576 Kalyani Nair et al

Figure 1. Caged ball valves. (a) Hufnagel–Lucite valve, (b) Starr–Edwards, (c) Smeloff–Cutter,(d) McGovern–Cronie, (e) DeBakey–Surgitool and (f) Cross–Jones.

2. History of mechanical valve

The pioneering efforts of Dr. Charles Hufnagel, who made the first successful placement of a

totally mechanical valvular prosthesis, started the era of artificial heart valves [1,2]*. Hufnagel

achieved this feat in 1952, by inserting a Plexiglas cage containing a ball occluder into the

descending thoracic aorta. The first implant of a mitral valve replacement in its anatomic

position took place in 1960, when the Starr-Edwards prosthesis was put the clinical use [3].

A number of similar caged ball designs appeared subsequently; like the Magovern–Cromie,

DeBakey–Surgitool, Smeloff–Cutter prostheses (see figure 1).

Even though caged ball valves have proven to be durable, their centrally occluding design

results in a larger pressure drop across the valve and higher turbulent stresses, distal to the

valve. Their relatively large profile increases the possibility of interference with anatomical

structures after implantation. This led to the development of low-profile caged disc valves in

the mid-1960s. The Cross–Jones, Kay–Shiley and Beall caged-disc designs were introduced

during 1965 to 1967 [4]. These valves were used exclusively in the atrio-ventricular position.

However, because of high complication rates, this model soon fell into disuse.

The next significant development was the introduction of tilting disc valves by Bjork–

Shiley in 1967 [4]. The design concept of this valve involves a free-floating disc, which in

the open position tilts to an angle depending on the design of the disc-retaining struts. In

the open position it acts like an aerofoil, with the blood flowing over and around it, thus

minimising the flow disturbance. The original Bjork–Shiley prosthesis employed a Delrin

*References in this paper are not in journal format


6

failure. It can also be breaking, including

brittle failure or fracture. Mechanical

properties of a material in the range of elastic

behavior include its elastic modulus under

tension and shear stresses, its Poisson’s ratio,

its resilience, and its flexural modulus. The

transition to failure is denoted by the yield

stress or breaking strength of the material.

During the last fifty years of development, a

set of material requirements for valves have

evolved which can be summarized as [18]

below:

Cause minimal trauma to blood elements

and the endothelial tissue of the

cardiovascular structure surrounding the

valve;

Show good resistance to mechanical and

structural wear;

Minimize chances for platelet and

thrombus deposition;

Be non-degradable in the physiological

environment;

Neither absorb blood constituents nor

release foreign substances into the blood;

Have good processibility (especially

suitable for sterilization of the device by

appropriate means) and take good surface

finish.

Problems that interfere with the

successful performance of valves can be

grouped as below:

Degradation of valve components;

Structural failure;

Clinical complications associated with the

valve.

Clinically, valve failure has been

considered to be present if any of the

following events require reoperation and/or

cause death:

Anticoagulant-related hemorrhage (ACH);

Prosthetic valve occlusion (thrombosis or

tissue growth);

Thromboembolism;

Prosthetic valve endocarditis (PVE);

Hemodynamic prosthetic dysfunction,

including structural failure of prosthetic

components (strut failure, poppet escape,

ball variance);

Reoperation for any other reason (e.g.:

hemolysis, noise, and incidental).

The performance of mechanical valves is

in several ways related to valve design and

structural mechanics. The design

configuration affects the load distribution

and dynamics of the valve components,

which in conjunction with the material

properties determine the durability and

successful performance of the valve. The flow

engendered by the geometry of the

components determines the extent of flow

separation and high shear regions. The

hinges in the bileaflet and tilting disc valves

can produce regions of flow stagnation,

which may cause localized thrombosis, which

may in turn restrict occluder movement. [18,

19]

Biochemical degradation and mechanical

wear is often inter-related, since degradation

accelerates material removal from surface

due to wear, which in turn accelerates the

rate of the biochemical reaction by

continually exposing new surface to the

corroding media. The use of large surface

areas of exposed metal in valves is often

quoted as leading to thromboembolic

complications. A cloth covering on the metal

can sharply reduce these complications, but

other problems associated with fabric wear

or uncontrollable tissue proliferation that

restricts flow can arise. The degradation of

the silicon-rubber balls used in ball valves

provides a good development in mechanical

heart valve prosthesis example of

deterioration caused by biochemical

incompatibility and also leads to mechanical

failure.

Under the conditions used, namely high

flow rate, all of the materials are reasonably

non-thrombogenic. Very small surface cracks

have been demonstrated to initiate thrombus

formation, presumably due to a small volume

of stagnant flow. In spite of desirable


7

characteristics of the biomaterials used in the

heart valves prosthesis, problems of

thromboembolic complications continue to

occur at the rate of 1 to 3% per patient year

in these valves. The mechanical stresses

induced by the flow of blood across the valve

prosthesis have been linked to blood damage

and activation of formed elements (red blood

cells, white blood cells and platelets)

resulting in the deposition of thrombi in

regions of relative stasis in the vicinity of the

valve. [20]

The pressure distribution on the leaflets,

and impact forces between the leaflets and

guiding struts are also being experimentally

measured in order to understand the causes

of strut failure. The flow through the

clearance between the leaflet and the housing

at the instant of the valve closure and in the

fully closed position, and the resulting wall

shear stresses within the clearance are also

suggested as being responsible for clinically

significant hemolysis and thrombus

initiation. Further improvements in the

design of the valves based on the closing

dynamics as well as improvements in

material may result in minimizing

thromboembolic complications as well as

occasional structural failure with implanted

mechanical valves. [18-20]

33.. HHeeaarrtt CClloonniinngg

Existing methods of treatment are not

quite effective in repairing damaged heart

muscle in end-stage cardiovascular diseases.

New research suggests that stem cells can

regenerate into heart cells. Nandini

Patwardhan traces the significance of stem

cells in the cardiovascular segment. [13]

Stem cells can be used for any kind of

myocardial infarction (heart attack) like

acute myocardial infarction, chronic

myocardial infarction and congestive heart

failure. However, it is advisable to treat

patients with myocardial infraction at the

earliest, preferably within 20-25 days of

heart attack. “Stem cells help reduce cardiac

infarction and improve ejection fraction,”

reveals Totey. Also, stem cells can be injected

in patients with cardiac myopathy. “Cardiac

myopathy is a condition, in which, the heart

muscle gets inefficient. And therefore, the

pumping efficiency of the heart or ejection

fraction as it is called, decreases to the extent

that the patient starts to feel breathless and

unable to function and heart failure occurs,”

explains Dr Ashok Seth, Chairman and Chief

Cardiologist, Max Heart & Vascular Institute,

Delhi. [21]

After a person gets a heart attack, the

cardiomyocites can die within 20 minutes

due to the occlusion of the artery. Once dead,

the heart starts remodeling itself to maintain

the normal cardiac output and to meet the

demands of the body. Stem cells, if injected at

the appropriate time, help in regenerating

the damaged muscles and healing the scarred

tissue, thereby, bringing the cardiac functions

to almost normal without causing

remodeling.

Figure 7: Heart steam cells were injected in the "skeleton" of a

heart and placed it in an incubator. Days later, the new heart

started beating.

Studies undertaken in small and big

animals have proved that when injected with

stem cells, they have the ability to home in on

the diseased muscles and then change

lineage. But the question that arises is, how

do these cells multiply into the desired

muscle cells? “For instance, when we inject

stem cells into the heart, they know exactly

where they have to home in, based on the

chemo attraction. The dead muscle gives out

certain chemocytes, which attract stem cells


8

to go there and convert into that lineage,”

states Shah. “Before we ventured on to

humans, we have seen this being proved

through various experiments on small and

big animals,” he adds. Unfortunately, there is

no way to control multiplying stem cells into

different non-desirable tissues. “However,

there is not a single report which shows that

stem cells, after injection into particular

organ, have developed into undesirable

tissue or cells. That shows that stem cells

injection are quite safe,” reveals Totey. [21]

The process of injecting stem cells is not a

very long drawn process. “We inject stem

cells by the intra-coronary method. This

means, we inject them into the coronary

artery—the culprit artery of the patient. The

muscle which is subtended by this artery,

which has been blocked, is our area of

interest,” discloses Shah.

A guiding catheter is put into the coronary

artery. Then a wire is sent over it into the

culprit artery. A balloon is sent on the wire.

Once inside the artery, the balloon is inflated

to stop the blood supply for a couple of

minutes. A lumen is inserted, through which a

million stem cells, cultivated from the bone

marrow of the patient, are injected in the

artery. The stem cells reach the target area,

where they have to home in. The balloon is

inflated till the stem cells are injected so that

blood does not flow during the process. “We

keep the balloon inflated for two to three

minutes, inject the stem cells and deflate the

balloon. Again after three to four minutes, we

repeat the procedure till all the stem cells are

injected,” explains Shah. “On an average we

inject 100 million stem cells. However, we

are doing it arbitrarily right now,” he adds.

44.. TToottaall AArrttiiffiicciiaall HHeeaarrtt

A total artificial heart (TAH) is a device

that replaces the two lower chambers of the

heart. These chambers are called ventricles

(VEN-trih-kuls). You may benefit from a TAH

if both of your ventricles don't work due to

end-stage heart failure. [22]

You may need a TAH for one of two reasons:

To keep you alive while you wait for a

heart transplant;

If you're not eligible for a heart transplant,

but you have end-stage heart failure in

both ventricles.

The TAH is attached to your heart's upper

chambers—the atria (AY-tree-uh). Between

the TAH and the atria are mechanical valves

that work like the heart's own valves. Valves

control the flow of blood in the heart. (For

more information, go to the Health Topics

How the Heart Works article.)

Currently, there are two types of TAH.

They're known by their brand names: the

CardioWest and the AbioCor. The main

difference between these TAH’s is

CardioWest is connected to an outside power

source and AbioCor isn't.

CardioWest has tubes that, through holes

in the abdomen, run from inside the chest to

an outside power source.

Figure 8: A - shows the normal structure and location of the

heart. B - shows a CardioWest TAH. Tubes exit the body and

connect to a machine that powers and controls how the

CardioWest TAH works.

AbioCor is completely contained inside the

chest. A battery powers this TAH. The battery

is charged through the skin with a special

magnetic charger.

Energy from the external charger reaches

the internal battery through an energy

transfer device called transcutaneous energy

transmission, or TET. [22]

http://www.nhlbi.nih.gov/health/health-topics/topics/hf/


9

An implanted TET device is connected to

the implanted battery. An external TET coil is

connected to the external charger. Also, an

implanted controller monitors and controls

the pumping speed of the heart.

Figure 9: A - shows the normal structure and location of the

heart. B - shows an AbioCor TAH and the internal devices that

control how it works.

Therefore, a TAH usually extends life for

months beyond what is expected with end-

stage heart failure. If you're waiting for a

heart transplant, a TAH can keep you alive

while you wait for a donor heart. It also can

improve your quality of life. However, a TAH

is a very complex device. It's challenging for

surgeons to implant, and it can cause

complications. [22]

Currently, TAHs are used only in a small

number of people. Researchers are working

to make even better TAHs that will allow

people to live longer and have fewer

complications.

V. CONCLUSION

Some devices - such as the left ventricular

assist device and bioartificial liver - will

provide assistance while new therapies

incorporating stem cells, gene therapy, or

engineered tissues are employed to repair or

replace the damaged organ. Until these new

therapies can be developed and tested,

medical devices will play a crucial role in

facilitating organ recovery and, perhaps,

organ salvage through natural repair

mechanisms. Where organ recovery is not

possible, artificial organs - when fully refined

- will provide a substitute for natural organs.

There has been considerable

improvement in the durability and functional

efficiency of mechanical heart valves. These

improvements have been by gradual

incremental improvements coupled with a

few revolutionary advances like the

introduction of tilting disc/bileaflet valves.

Despite all these improvements,

complications (though their rates are very

low) continue to be associated with their use.

All current models of mechanical heart valves

need anti coagulation therapy to minimize

the risk of thrombosis and embolism.

Management of anticoagulation levels and

bleeding are other concerns.

Recent trends in the choice of materials

indicate a preference towards soft occluder

materials. One team in Germany is working

towards bileaflet valves with soft occluders.

Medtronic– Hall also had announced that

they will be looking for a valve with soft

occluder in the near future. The advantages

of using soft occluder material are many.

They absorb the impact forces generated

during valve closure, there by reducing the

chance of suture dehiscence. The reduction

in the impact forces also reduces the load

that needs to be transferred to the

surrounding tissues through the suture ring,

reducing the irritation caused by the

continuous movement at the cloth–metal

interface. Another improvement caused by

the soft occluder is the reduction in the

probability of occurrence of cavitation and

cavitation damage. This has been reason-

ably established by various studies

conducted on Chitra heart valve, which

showed that even at very high loading rates,

the chance for cavitation in valves with soft

occluders is minimum.


10

REFERENCES

[1] http://www.bmecentral.com/artificial-

organs.html (last login in 16/05/2012);

[2] MILLER, G., Artificial Organs, Synthesis

Lectures on Biomedical Engineering, 2006, doi:

10.2200/S00023ED1V01Y200604BME004;

[3]

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