Artificial heart

ARTIFICIAL HEART Ahmed Abdelfatah HussienBiomechatronics

IntroductionDEFINITION

“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.”

An artificial heart is a mechanical device, about the size of an orange, that is connected to your heart or implanted in your chest to help or replace a failing heart. It may have several valves, a mechanism to propel blood forward, and one or more chambers.

Sometimes an artificial heart may help your heart temporarily, until yours recovers. If this is the case, the artificial heart will be removed when it is no longer needed. More commonly, when there is irreversible heart muscle damage and your heart can t recover, the artificial heart stays until you can have a heart transplant. If no other options are available, an artificial heart may completely and permanently replace your heart.

Human Heart

Heart consists of:Right Atrium and Ventricle AtriumLeft Atrium and Ventricle

Two Types of Valves:

Atrioventricular Valve: separates the atrium from the ventricle

Semi-Lunar Valve: separates the ventricles from the outgoing blood vessels

Human Heart

Right Atrioventricular Valve: Tricuspid Valve Left Atrioventricular Valve: Bicuspid Valve Right Semi-Lunar Valve: Pulmonary Valve Left Semi-Lunar Valve: Aortic ValvePurpose of Valves: Prevent backflow, or flow of blood back into chamber from which it came

Human HeartHeart Function: When the heart is at rest the right atria

is filled with oxygen free blood returning from the body. While the left atrium receives oxygen rich blood from the lungs.

After the atria fill an electrical impulse causes them to contract forcing open valves that lead to the ventricles.

The same electrical impulse causes the ventricles to contract about a tenth of a second later pushing the blood through another set of valves that lead to the lungs and the rest of the body.

History1972- Robert Jarvik created the 1st human artificial heart made of polyester, plastic, & aluminum. It was implanted in cows.

1981- The 1st artificial heart was approved for human implantation. (Jarvik-7)

1982- Barney Clark received the 1st implantation performed by William DeVires of the University of Utah1994- The FDA approved the Ventricular Assist Device (VAD) which was the 1st wearable device to assist the left ventricular

2004- The 1st Total Artificial Heart (TAH) was approved by the FDA by Cardio West.

Jarvik-7 Artificial Heart The Jarvik-7 design incorporates two

heart pumps that are connected to a power console.

Each pump is small enough to be implanted into the void that was left behind from the extraction.

Both pumps receive power from a large external console. The console pushes air through the tubing.

Air enters inside the pump and is expelled through a series of thin flexible diaphragms.

The doctors monitor the patients cardiac output and heart rate from a power console a seven feet away from where the patient rests.

AbioCor Artificial HeartPatients with an implanted AbioCor heart will still have atria that beat at the same time, but the artificial heart, which replaces both ventricles, can only force blood out one ventricle at a time. So, it will alternately send blood to the lungs and then to the body, instead of both at the same time as a natural heart does. The AbioCor is able to pump more than 10 liters per minute, which is enough for everyday activities.

What research is being done into artificial hearts?Research is being done in several areas to improve the quality and use of artificial hearts. Researchers are looking into reducing the size of artificial hearts so that they

can be totally implanted inside the chest. Work is also being done to develop artificial heart batteries that are small,

long-lasting and implantable, and which can be recharged across the patient s skin.

Biologically superior materials are being developed to reduce the tendency for blood to clot and the need for blood-thinning medicines (anticoagulants). These materials will be used to line the internal chambers of artificial hearts.

Research is also being done into stem cells, which may be used to replace damaged heart muscle cells and restore heart muscle function. If this is possible, it would prevent heart failure and ultimately reduce the need for heart transplants and artificial hearts.

Artificial Heart valve An artificial heart valve is a

mechanism that mimics the function of a human heart valve

It’s used for patients with a heart valvular disease or have a damaged valve

Heart valves are used to provide the heart with a unidirectional blood flow

When Heart Valves Stop Working Heart Valve diseases fall into two

categories:

stenosis- hardening of the valve

incompetence- permittence of backflow

3 causes of Heart Disease: Rheumatic Fever: stiffens valve tissue,

causing stenosis Congenitally defective valves: do not

form properly as the heart develops, but often go unnoticed until childhood

Bacterial infection: causes inflammation of valves, tissue scarring, and permanent degradation

Artificial Heart Valve Types

Evolution of Prosthetic Heart Valves

The development of the original ball-and-cage valve design can be attributed to the bottle stopper in 1858

In the early 1950’s, it led to the idea of a prosthetic heart valve consisting of a cage with a mobile spherical poppet

This first heart valve was made of a Plexiglass(methyl methacylate)cage surrounding a silicone-coated nylon poppet

First implanted in a human in a closed procedure in September of 1952 (descending thoracic aorta)


Significant advances were made soon after to help the development of the heart valve:

In 1953, marked successful use of the heart and lung machine, paving the way for the 1st open heart operations

The idea of using blood from another patient to oxygenate the blood of the patient was developed

New methods were came for evacuating air from the heart

New materials (Plexiglass, Teflon, and Dacron)


On July 22, 1955, at the City General Hospital in Sheffield, England, Judson Chesterman implanted the first successful heart valve

The patient lived 14 hours after the valve was placed, but died when the poppet twisted out of position

Valve was made of Perspex, an outer cage, a poppet, and 2 buttons to fasten the valve to the outside of the heart


Starr-Edwards valve was first successful long-term valve created

It was implanted in its first 8 patients in 1961 (6 of 8 survived

Ball-and-Cage design Devised important “Nine

Commandments” in developing a prosthetic heart valve


“Nine Commandments”: Embolism Prevention Durability Ease and Security of Attachment Preservation of Surrounding Tissue Function Reduction of Turbulance Reduction of Blood Trauma Reduction of Noise Use of Materials Compatible with Blood Development of Methods of Storage and Sterilization


Since this time, over 30 mechanical heart designs have been marketed in the U.S. and abroad

These valves have progressed from the simple caged ball valves, to strut-and-leaflet valves and the modern bileaflet valves, to human and animal tissue


Mechanical Valves:Ball Valves

This design uses a spherical occluder, or blocking device, held in place by a welded metal cageProblem and Why failed: Natural heart

valves allow blood to flow straight through the center of the valve (central flow)

Caged-ball valves completely blocked central flow and collisions with the occluder ball caused damage to blood cells

Finally, these valves stimulated thrombosis, or formation of blood clots

Starr-Edwards Ball Valve

Model: Starr-EdwardsType: Aortic Caged BallMaterials: Silicone Rubber ball with

2% barium sulfate, cage-Stellite alloy No. 21, sewing ring- knitted Teflon and polypropelene cloth

1 of 4 Starr-Edwards models developed are still used today, and is the only ball valve currently used in U.S.

Magovern-Cromie Ball Valve

Model: Magovern-Cromie valve

Type: Aortic Caged Ball

Materials: Ball-Silicone rubber with barium, cage-titanium, sewing ring-none, Cage open at top

Smeloff-Suttor Ball Valve

Model: Smeloff-Suttor valveType: Aortic, Mitral, Tricuspid caged

ball

Materials: Ball-Silicone rubber, cage-titanium, sewing ring-Teflon

Problems: Ball Variance, swelling of ball from lipid absorbtion, can cause sticking of ball in inflow orifice

Mechanical Valves:Single Leaflet Disc Valves

Uses a tilting occluder disk to better mimic natural flow patterns through the heart

tilting pattern allow more central flow while still preventing backflow

Some damage still occurs to blood cells

Reduces thrombosis and infection, but does not eliminate either problem

Mechanical Valves:Single Leaflet Disc Valves

Bjork- Shiley Standard Aortic Valve

Model: Bjork- Shiley Standard

Type: Aortic Tilting Disc

Materials: Disk- Pyrolytic Carbon, cage-Haynes 25, sewing ring-Teflon

Medtronic-Hall Valve

Model: Medtronic-Hall A7700 (aortic), M7700 (mitral)

Type: Aortic and Mitral Tilting Disk

Materials: Cage-titanium, Disk-Pyrolytic carbon, sewing ring-knitted teflon

Other Single Leaflet Disc Valves

Another similar valve is the caged disc valve

Examples are Starr-Edward Model 6500 and the Kay-Shiley Model

Mechanical Valves:Bileaflet Disc Heart Valves

Consists of two semicircular leaflets that pivot on hinges integrated onto the flange

Carbon leaflets and flange exhibit high strength and excellent biocompatibility

Provide closest approximation to central flow

Allows small amount of backflow as leaflets cannot close completely

Mechanical Valves:Bileaflet Disc Heart Valves

St. Jude Bileaflet Valve

Model: St. Jude Valve Standard

Design :Mitral, Aortic, Tricuspid Bileaflet Valve

Materials-Cage and disk- pyrolytic carbon, sewing ring-double velour knitted polyester

Animal Tissue Valves

Heterograft or Xenograft Valves

Most commonly used tissues are the porcine (pig) valve tissue and Bovine (cow) pericardial tissue

Porcine (pig) Valves

Two major brands of porcine available today, Hancock and Carpentier-Edwards

Has good durability and and good hemodynamics

Materials: Porcine valve tissue, stents made of wire, Elgiloy(cobalt-nickel alloy), sewing ring-knitted Teflon

Pericardial (cow) Valves

Lasts as long as standard porcine valves at 10 years

The pericardial valve has excellent hemodynamics, even in smaller sizes(19mm to 21mm)and has gained a large market share (about 40% of US tissue valves) in this group of patients

Stentless Porcine Valve

Stentless valves are made by removing the entire aortic root and adjacent aorta as a block from the pig

Drawbacks: Valve is more difficult to implant and requires special measurements for successful implantation

Homografts(Human to Human) Homografts are valves transplanted from

one human to another After donation, valves are preserved in

liquid nitrogen(cyropreserved) until needed

Since the valve must be thawed overnight, the patient’s size must be known beforehand

As with heart transplants, homograft availability is limited by donor availability

Autografts (Ross Procedure) Autografts are valves taken from the same

patient in which the valve is implanted Used for patients with diseased aortic valves Advantages: patient receives a living valve in the

aortic position Better durability and hemodynamics Disadvantages: difficult procedure for the

surgeon and involves considerable skill and time most common problem is leakage of the valve

(aortic regurgitation)

Animal Tissue Valves vs. Mechanical Valves

With the animal tissue, patients do not need lifelong anticoagulant therapy required with mechanical valves

Animal tissue is also inexpensive and mass-produced However, animal tissue has uncertain durability (5-15 years

)that will inevitably require a risky re-operation Mechanical valves can also fail suddenly and

catastrophically Have serious problem with thromboembolism Tissue heart valves – Wear, there is a small possibility that

the body will reject the valve, inability to implant them into infants and children

Mechanical disadvantage- is cavitation, when the rapid change in pressure drop will form vaporous micro bubbles. This will cause blood cell damage.

Algorithm for selecting a valve procedure

Future of heart valve replacement Polymeric Heart Valves - Scientists are looking more into

polymer materials for heart valves because it’s easy to fabricate, has a large range of polymer properties, and durability.

Tissue engineered heart valves- Obtaining the number of types of cells for tissue valves, lack of scaffold material

Tissue engineered heart valves: better biocompatibility, less infection, life expectancy of valve increase, To make artificial heart valves compatible for children.

Engineering

Artificial heart