Artificial Heart

According to the American Heart Association, an estimated 550,000 new cases of heart failure are diagnosed each year.

An artificial heart is a device designed to completely replace a seriously damaged heart, temporarily take over the function of a failing heart until a donor heart is available for heart transplant, or perform the job of a natural heart during surgery. The two major types of artificial heart are the heart-lung machine and the mechanical heart. The heart-lung machine consists of a pump, which performs the heart's job of pumping blood, and an oxygenator, which performs the lungs' job of supplying oxygen to the blood. This machine is mainly used by surgeons to stop and restart the heart during heart surgery.

A mechanical heart, on the other hand, may be a self-contained artificial heart or a left ventricular assist device (LVAD). The self-contained artificial heart is designed for patients who cannot be helped by any other means and are not eligible for heart transplant. It is also called a total artificial heart because it contains its own power source. The LVAD, on the other hand, is designed to work alongside the heart, taking on the workload of the left ventricle while the patient awaits a heart transplant. The left ventricle, responsible for the pumping action of the heart, is the hardest working of the four chambers (sections) of the heart. It performs about 80 percent of the heart's work and, as such, is usually the part that is weakened by disease.

A tireless worker

The heart is a hard-working organ that continually moves blood throughout the whole body. It has four chambers. The upper chambers, or the atria (singular: atrium), receive the blood that flows back to the heart through the veins. The lower chambers, or the ventricles, pump the blood out of the heart through the arteries.

Blood enters the right atrium through the veins and fills the right atrium. The right atrium pumps the blood through a valve into the right ventricle, which in turn pumps the blood to the lungs through another valve. The person breathes out carbon dioxide and breathes in oxygen. The oxygen-rich blood goes back to the heart, entering through the left atrium. The left atrium sends the blood into the left ventricle, which pumps it out to the body through the aorta, the largest artery of the body. Smaller blood vessels branching out of the aorta carry the blood to different parts of the body.

Heart failure

Congestive heart failure is the steadily declining ability of the heart to pump blood. It is one of the leading causes of death. Some people are born with a defective heart or may have caught a virus that damaged the heart. In others, the disease may be caused by high blood pressure, sudden damage from a heart attack, or other medical problems. Still others have developed the disease as a result of smoking, eating foods high in fat and cholesterol, not exercising, or being overweight. According to the American Heart Association, almost five million Americans suffer from heart failure, and an estimated 550,000 new cases are diagnosed each year. Although it usually affects older people, heart failure is also seen in children and young people.

FAMOUS FIRSTS

In 1967, South African doctor Christiaan Barnard (1922–2001) performed the world's first human heart transplant. Barnard replaced the failing heart of Louis Washkansky with that of a young woman killed in a car accident. Washkansky survived for eighteen days.

On December 18, 1985, 41-year-old Mary Lund became the first woman to receive an artificial heart. The Jarvik-7, which had been designed for adult males, had to be modified in size to fit her. The artificial heart supported Lund's natural heart while she waited for a heart transplant.

First artificial hearts

Since the late 1800s, medical researchers have tried to develop a mechanical device to temporarily take over the heart's function of pumping blood. In 1935, American surgeon John H. Gibbon (1903–73) invented the first heart-lung machine. It took him nearly twenty years to perfect his invention. In 1953, Gibbon used the machine to perform the first open-heart surgery on an 18-year-old patient. Four years later, Dr. Willem Kolff (1911–), a Dutch-born physician, implanted the first artificial heart into a dog.

While Kolff was working on building a total artificial heart, other researchers were developing artificial devices for patients who were waiting for a heart transplant or for those whose hearts were not functioning fully. In 1963, Dr. Michael DeBakey (1908–) implanted a pump with internal valves in a patient. The plastic banana-shaped device helped move the blood through the chambers of the heart. In 1966, Dr. Adrian Kantrowitz (1918–) implanted a partial mechanical heart in a human. That same year, DeBakey implanted the first LVAD.

Denton Cooley (1920–) and his surgical team at the Texas Heart Institute (Houston, Texas) performed the first temporary human artificial heart implant in 1969, using a device designed by Argentine-born Domingo Liotta (1924–). The artificial heart was a double-ventricle pump, made of plastic and synthetic polyester fabric. It was air-driven by an external console, a cabinet-like structure about the size of a home washing machine with a control panel. The artificial heart kept Haskell Karp alive for almost three days, after which time he had a heart transplant.

A complete replacement heart

The first time that an artificial heart totally replaced a diseased human heart occurred on December 2, 1982. Dr. William DeVries (1943–) implanted the Jarvik-7 heart into Barney Clark (1921–1983). Clark was too sick to qualify for a donor heart, so the device would be a permanent heart for the 61-year-old patient. Named after its inventor, Dr. Robert Jarvik (1946–), the artificial heart was slightly bigger than the human heart and weighed about the same (10 ounces, or 280 grams). The device was made of plastic on an aluminum base and consisted of two pumping ventricles (lower heart chambers) connected to the upper chambers of the patient's heart. The pumping action came from compressed air delivered by an electrical console outside the patient's body. Two air hoses, inserted through abdominal incisions (cuts), were connected to the artificial ventricles. Clark survived for 112 days before finally dying from infection and blood vessel blockage resulting from blood clots.

DeVries performed four other implants using the Jarvik-7. The patients eventually died, including William Schroeder (1932–1986), who lived for 620 days. Further ventures in inventing a permanent artificial heart came to a halt, especially because of the problems encountered in its use—the formation of blood clots that traveled to the brain, causing strokes; the occurrence of infection due to the abdominal incisions and the opening of the patient's chest during surgery; and the patient's inability to move around because of the bulky console that was about the size of a home refrigerator.

Redesigning the artificial heart

In the 1990s, medical researchers turned their attention to designing mechanical devices to help weakened hearts function until a donor heart was available. In 1994, the U.S. Food and Drug Administration (FDA), the government agency responsible for approving medical devices, approved such a device. The HeartMate® Implantable Pneumatic Left Ventricular Assist System (IP LVAS) was a titanium alloy pump implanted in the abdominal area and connected to the left ventricle. From the left ventricle, the device pumped the blood into the aorta, supplying the whole body with blood. The device was powered by an external console on a movable cart, which ran on electricity or battery (for thirty minutes).

In 1998, the FDA approved portable versions of the LVAD that are powered by a small external battery-run computerized controller worn at the waist or under the arm. The two rechargeable batteries have to be charged every six to eight hours. The devices usually have backup batteries and a hand pump that the patient can operate.

Design

Several important issues must be addressed when designing a LVAD. The designer has to make sure that enough blood is pumped. The external console must have a fixed mode as well as an automatic mode so that the pump can be adjusted to adapt to the patient's needs. The fixed mode ensures that the pump rate is the same all the time, while the automatic mode enables the system to make adjustments to the blood flow depending on what the patient requires.

The designer must also make sure that no blood clots are created. Materials must be biocompatible, which means that they must be able to coexist with the body tissue and not be rejected by it. Otherwise, the pump could fail. For the same reason, the total weight and size are important considerations. Some LVADs weigh as little as 1.25 pounds (570 grams) and measure about 2 inches (5 centimeters) thick and 4 inches (10 centimeters) in diameter. In addition, the motor must run at its most efficient level so that minimal heat is generated.

A LVAD pump generally consists of a blood chamber, an air chamber, inflow and outflow tubes, and a driveline for connecting to the external power source. The inflow tube attached to the left ventricle moves the blood to the blood chamber. An external control starts the pumping action. A pusher plate "pushes" the flexible diaphragm (separating membrane between the two chambers) upward, thus pressurizing the air chamber. This action ejects the blood through the outflow tube attached to the aorta, pumping the blood to all parts of the body.

Raw Materials

Since the left ventricle is the hardest-working of the four chambers of the heart, it is the most likely to get weak. The completely implantable artificial heart (the AbioCor™; see The Future) is still undergoing human testing; therefore, LVADs, currently the most widely used of the artificial hearts, will be discussed here. As of 2002, over 4,000 LVADs had been implanted in patients worldwide waiting for a heart transplant.

The LVAD is made of metal, plastic, ceramic, and animal parts. A titanium-aluminum-vanadium alloy is used for the pump and for other metal parts because it not rejected by the patient's body. The titanium parts are shaped at a specialized titanium processor and, except for surfaces that will have contact with blood, the titanium is given a certain finish. Blood-contacting surfaces are bonded with special titanium microspheres, which are tiny beads of titanium that produce textured surfaces.

A diaphragm within the pump is made from plastic polyurethane that is also textured. The textured surfaces of the titanium and the diaphragm are very important. When blood comes in contact with the textured surfaces, it deposits circulating blood cells, which stick to the surfaces, creating a living lining inside the device that resembles the inner surfaces of veins (blood vessels that return blood to the heart) and arteries (blood vessels that carry blood away from the heart). This helps prevent the formation of blood clots inside the LVAD.

The two tubular grafts that are used to attach the LVAD to the aorta and the left ventricle are made from polyester. The valves used are actual heart valves from a pig. The motor is made from titanium or other metals and ceramics.

The Manufacturing Process

Most components of the LVAD are made according to specifications by third-party manufacturers, including machine shops and manufacturers of the printed circuit board. A medical-device firm that specializes in heart valves sews the valves inside the tubular grafts with sutures.

Forming the plastic polyurethane parts

1 Some LVAD manufacturers make their own plastic polyurethane parts. One process uses a plastic liquid solution that is made by the manufacturer. This solution is poured on a ceramic mold layer by layer. Each layer is heated and dried until the desired thickness is achieved. The part is then removed from the mold and inspected. The polyurethane parts may be made by an outside manufacturer using injection molding, in which melted plastic is forced into a mold under high pressure and then allowed to cool. As it cools, the plastic assumes the shape of the mold.

Assembly

2 Each LVAD takes several days to assemble and test. The assembly takes place in a clean room to avoid contamination. Each LVAD consists of up to fifty components that are put together with special adhesives that have been strengthened at high temperatures.

3 Several assembly operations are done at the same time, including the assembly of the motor housing and components, the attachment of the pusher plate to the polyurethane diaphragm, and the assembly of the percutaneous tube. The percutaneous (administered through the skin) tube, as its name implies, is a small tube containing control and power wires that pass through the patient's skin and connect the LVAD to the power source. These subassemblies are individually inspected. The complete system is then put together. The tubular grafts are assembled separately and attached during surgery.

Testing

4 After the components are put together, each device is tested, using special equipment that mimics conditions the device would encounter once implanted in the body. All electronic parts are also tested to ensure the proper functioning of all electric circuitry.

Sterilization and packaging

5 After the LVAD has passed the testing, it is sent to an outside service for sterilization to destroy germs that may cause infection. Each device is sealed in plastic trays and returned to the heart manufacturer. It is then packaged in specially made suitcases to protect it from contamination and to prevent damage.

The Future

Heart disease remains the number one cause of death in the United States. As baby boomers (people born between 1946 and 1964) age, the number of people in need of healthy hearts will increase dramatically. Each year, an estimated 45,000 Americans need a heart transplant; however fewer than 3,000 donor hearts are available. Faced with this problem, scientists continue to develop artificial hearts as potential alternatives.

On July 2, 2001, the first-ever completely self-contained artificial heart (with power supply included) was implanted in a human. Drs. Laman Gray and Robert Dowling of the University of Louisville, Kentucky, removed Robert Tools's damaged heart, while leaving major blood vessels on which to attach the AbioCor™ Implantable Replacement Heart. Jointly developed by the Texas Heart Institute and Abiomed, Inc., the device is about the size of a softball and weighs 2 pounds (907 grams). Robert Tools died on November 30, 2001, from complications, which, according to his doctors, were unrelated to his artificial heart. Tom Christerson became the world's second recipient of the AbioCor™ Implantable Replacement Heart on September 13, 2001. Prior to his artificial-heart surgery, Christerson was not expected to live more than a month. On April 16, 2002, he was able to go home to his family. As of June 18, 2002, Drs. Gray and Dowling announced that the patient was doing well.

The AbioCor™ heart is powered by an external battery that passes electricity through the patient's skin (without any skin piercing) to a power receptor in the chest. An electronic monitor is implanted in the abdominal area to regulate the pumping speed. An internal battery continually charged by the external batteries serves as an emergency power source, as well as allows the patient to perform certain activities, such as take a shower, without the batteries. In January 2002, the manufacturer of AbioCor™ announced that it had removed a plastic cage in the design that may have caused blood clotting and led to stroke in at least one patient. The AbioCor™ heart will likely undergo different stages of testing before it can be commercially sold. In the meantime, Abiomed, Inc. is working on a smaller version of the AbioCor™ heart.

Pennsylvania State University researchers had also been developing a complete artificial heart. In September 2000, Abiomed, Inc., acquired the rights to the Penn State Heart. Abiomed and Penn State's College of Medicine will work together to continue developing the device.

Several heart-assist devices are also undergoing various stages of testing. The Kantrowitz CardioVad™, developed by Dr. Adrian Kantrowitz, is the only device that allows a patient to turn it on and off. Krantrowitz, the first U.S. surgeon to perform a heart transplant, spent thirty years fine-tuning the device. It is designed for patients with chronic (recurring) congestive heart failure who are not qualified for a heart transplant. It has three main parts—a pumping bladder weighing less than 1 ounce (about 28 grams), a couple of tubes leading from the pumping bladder (one for sending information to an attached computer and the other for inflating and deflating the bladder), and an external power source. The patient receives two power sources, a 5-pound, (2.3-kilogram) battery-powered unit and a unit the size of a small suitcase on wheels. Unlike other open-heart surgeries to implant heart devices, in which the breastbone is split open, the procedure to insert the CardioVad™ involves going through two ribs on the left chest. The device is sewn into the aorta, and a wire is run through the abdomen for linkage to the power source.

IMPROVING THE QUALITY OF LIFE

Researchers supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health found, in a three-year study of patients with severe heart failure, that the use of a left ventricular assist device (LVAD) had helped extend the patients' lives. In addition, the medical device also improved their emotional state and physical function. These patients had been terminally ill and were ineligible for heart transplant due to their age or certain medical conditions.

Smaller types of LVADs are also being tested. The Jarvik-2000 Flow-maker, invented by Dr. Robert Jarvik, the inventor of the first replacement heart, Jarvik-7, is about the size of a C battery. The small titanium turbine pump fits into the left ventricle and is powered by an external battery.

Another small-sized LVAD has been invented by Dr. Michael DeBakey, Dr. George Noon (1934–), and NASA (National Aeronautics and Space Administration) engineers. Borrowing from space technology, the MicroMed DeBakey Ventricular Assist Device™ uses very light materials and computer chips. It weighs less than 4 ounces (113 grams) and has a simple moving part called the inducer-impeller. The titanium device, about the size of a walnut, plugs into the left ventricle and is powered by an external battery, connected by an inner-ear implant attached to the skull.

alloy:

A mixture of a metal and a nonmetal or a mixture of two or more metals.

aorta:

The main artery that carries blood away from the heart to the different parts of the body.

artery:

A blood vessel that carries blood away from the heart.

atrium:

One of the two upper chambers of the heart that receives blood from the veins and pumps it to the ventricles.

blood clot:

A solid mass of blood that can block the movement of blood.

chamber:

One of the four sections of the heart through which blood is pumped.

donor heart:

A healthy heart obtained from a person who has just died and used for such purposes as a heart transplant. Persons who have voluntarily given permission for their organs to be used after their death typically carry a donor card, stating their intent.

heart transplant:

Also called heart transplantation; the process of replacing a diseased heart with a healthy heart from a person who has just died.

stroke:

A sudden blockage or bursting of a blood vessel in the brain, interrupting the blood flow to part of the brain.

valve:

In living hearts, one of the four flaps of tissue between the chambers that prevents the backward flow of blood. In artificial hearts, the flap-like structure that allows blood to flow in one direction.

vein:

A blood vessel that returns blood to the heart.

ventricle:

Either of the two lower chambers of the heart, which receives blood from the atria, or upper chambers, and pumps it into the arteries.

For More Information

Books

Berger, Melvin. The Artificial Heart. New York, NY: Franklin Watts, 1987.

Yount, Lisa. "From Sausage Casings to Six-Million-Dollar People." In MedicalTechnology. New York, NY: Facts On File, Inc., 1998.

Periodicals

Rose, Eric A. et al. "Long-Term Use of a Left Ventricular Assist Device for End-Stage Heart Failure." The New England Journal of Medicine (November 15, 2001): pp. 1435–1443.

Westaby, Stephen et al. "First Permanent implant of the Jarvik 2000 Heart." TheLancet (September 9, 2000): pp. 900–905.

Web Sites

"Affairs of the Heart." Public Broadcasting System.http://www.pbs.org/saf/1104/features/substitute.htm (accessed on July 22, 2002).

"The Heart: An Online Exploration." The Franklin Institute Online.http://sln.fi.edu/biosci/heart.html (accessed on July 22, 2002).

"Heartmate® Implantable Pneumatic Left Ventricular Assist System." Texas HeartInstitute.http://www.bcm.tmc.edu/tmc/thi/iplvas.html (accessed on July 22, 2002).

Artificial Heart

Background

A natural heart has two pumps, each with two chambers. The right atrium pumps oxygen-depleted blood from the body into the right ventricle, which pumps it to the lungs. The left atrium sends aerated blood from the lungs into the left ventricle, which pumps it out to the body. With each heart beat, the two atria contract together, followed by the large ventricles.

Congestive heart failure, which is the steadily declining ability of the heart to pump blood, is one of the leading causes of death. This disease is caused by sudden damage from heart attacks, deterioration from viral infections, valve malfunctions, high blood pressure and other problems. According to the American Heart Association, an estimated five million Americans are living with heart failure and over 400,000 new cases are diagnosed every year. About 50% of all patients die within five years. Heart disease cost the United States health industry about $95 billion in 1998.

Though medication and surgical techniques can help control symptoms, the only cure for heart failure is an organ transplant. In 1998, around 7,700 Americans were on the national heart transplant list but only 30% received transplants. Artificial hearts and pump-assist devices have thus been developed as potential alternatives.

An artificial heart maintains the heart's blood circulation and oxygenation for varying periods of time. The ideal artificial heart must beat 100,000 times every 24 hours without requiring either lubrication nor maintenance and must have a constant power source. It must also pump faster or slower depending on the activity of the patient without causing either infection or blood clots.

The two major types of artificial hearts are the heart-lung machine and the mechanical heart. The first type consists of an oxygenator and a pump and is mainly used to keep blood flowing while the heart is operated on. This machine can only operate for a few hours since the blood becomes damaged after longer times.

A mechanical heart is designed to reduce the total work load of a heart that can no longer work at its normal capacity. These hearts consist of equipment that pulses the blood between heart beats or use an artificial auxiliary ventricle (left ventricle assist device, LVAD) that pumps a portion of the normal cardiac output. Because such devices usually result in complications to the patient, they have generally been used as a temporary replacement until natural hearts can be obtained for transplantation. Worldwide about 4,000 LVADs have been implanted. The market for these devices is estimated at $12 billion per year in the United States.

History

Since the late nineteenth century, scientists have tried to develop a mechanical device that could restore oxygen to the blood and remove excessive carbon dioxide, as well as a pump to temporarily supplant heart action. It took almost 100 years before the first successful heart-lung machine was used on a human being by John H. Gibbon Jr. in 1953. Four years later the first artificial heart (made from plastic) in the western world was implanted inside a dog. The National Heart Institute established the artificial heart program in 1964, leading to the first total artificial heart for human use implanted in 1969.

The emphasis shifted to left ventricular assist systems and blood compatible materials in 1970. During that same year, a LVAD was used successfully. However, blood pump development continued and devices became smaller, lighter, more acceptable, and clinically successful. A number of polyurethane and plastic pumps of longlife time were also developed. During the 1980s, the Food and Drug Administration (FDA) imposed more restrictive rules to the Medical Devices Standards Act, leading to higher development costs. Many research groups had to drop out, with only a few remaining today.

Perhaps the most famous scientist is Dr. Robert Jarvik, who invented an artificial heart called the Jarvik-7. This device, made from aluminum and plastic, replaced the two lower chambers of the natural heart and used two rubber diaphragms for the pumping action. An external compressor the size of a refrigerator kept the artificial heart beating. Barney Clark was the first patient to receive this heart. He survived 112 days before physical complications caused by the implant took his life. In 1986, William Schroeder became the second Jarvik-7 recipient, surviving for about 20 months.

The medical community realized that a completely implantable heart could avoid the mobility and infection problems caused by the Jarvik-7. In 1988, the National Institutes of Health began funding development of such hearts and was supporting such a program in 1991 totaling $6 million. Three years later, an electric and battery-powered implantable LVAD became available. In 1999, Charlie Chappis became the first patient ever released from a hospital with such a device. Other artificial hearts of various designs are currently being tested.

Raw Materials

An artificial heart or LVAD is made out of metal, plastic, ceramic, and animal parts. A titanium-aluminum-vanadium alloy is used for the pump and other metal parts because it is biocompatible and has suitable structural properties. The titanium parts are cast at a specialized titanium processor. Except for blood-contacting surfaces, the titanium is machined to a specific finish. Blood-contacting surfaces receive a special coating of titanium microspheres that bond permanently to the surface. With this coating, blood cells adhere to the surface, creating a living lining.

A blood-contacting diaphragm within the pump is made from a special type of polyurethane that is also textured to provide blood cell adherence. Two tubular grafts are made from polyester (which are used to attach the device to the aorta) and the valves are actual heart valves removed from a pig. Other parts that make up the motor are made from titanium or other metals and ceramics.

Design

There are several critical issues when designing a LVAD. Fluid dynamics of the blood flow must be understood so that enough blood is pumped and no blood clots are created. Materials must be chosen that are biocompatible; otherwise the pump could fail. The efficiency of the motor must be optimized so that minimal heat is generated. Because of possible rejection, the total volume and surface area of the entire device should be kept as small as possible. A typical LVAD weighs around 2.4 lb (1,200 gm) and has a volume of 1.4 pints (660 ml).

Robert Jarvik was born on May 11, 1946, in Midland, Michigan, and raised in Stamford, Connecticut. He entered New York's Syracuse University in 1964, studying architecture and mechanical drawing. After his father developed heart disease, Jarvik switched to pre-medicine. He graduated in 1968 with a bachelor of arts in zoology, but was rejected by medical schools in the United States. He entered the University of Bologna in Italy, but left in 1971 for New York University, earning a master of arts in occupational biomechanics.

Jarvik applied for a job at the University of Utah. The director of the Institute for Biomedical Engineering and Division of Artificial Organs, Willem Kolff, had been developing an artificial heart since the mid-1950s. Jarvik began as his lab assistant, earning his medical degree in 1976.

On December 2, 1982, doctors transplanted the first artificial heart into a human. This plastic and aluminum device, the Jarvik-7, was implanted into Barney Clark, who survived for 112 days after the operation. Several other patients received Jarvik-7 hearts but none lived more than 620 days. The main benefits were that there wouldn't be a wait for a human heart and there was no chance of rejection. The obvious pitfall being patients were forever connected to a compressed air machine via tubes.

The Jarvik-7 was eventually used as a stopgap measure for patients awaiting natural hearts and provided hope that there would not be a wait for transplants. In 1998 Jarvik continued work on a self-contained device to be implanted into a person's diseased heart to make it function correctly.

The Manufacturing Process

• 1 Most of the components are made to custom specifications by third party manufacturers, including machine shops and printed circuit board manufacturers. The porcine valves are sewn inside the grafts with sutures at a medical device firm that specializes in heart valves.

  Once all components are obtained, the LVAD system is assembled and tested, to ensure that each device meets all specifications. Once tested, the LVAD can be sterilized and packaged for shipment.

Forming the polyurethane parts

• 2 Some artificial heart manufacturers make their own polyurethane parts. One process uses a proprietary liquid solution that is poured on a ceramic mandrel layer by layer. Each layer is heated and dried until the desired thickness is reached. The part is then removed from the mandrel and inspected. Otherwise, a third party manufacturer uses an injection molding or vacuum molding process combined with radio frequency welding.

Assembly

• 3 Each artificial heart takes several days to put together and test. The assembly process is performed in a clean room to avoid contamination. Each artificial heart consists of up to 50 components that are put together using special adhesives. These adhesives require curing at high temperatures. Several assembly operations happen in parallel, including the assembly of the motor housing and components, the assembly of the percutaneous tube and the attachment of the pusher plates to the polyurethane diaphragm. These subsystems are individually inspected, then final assembly of the complete system occurs. The grafts are assembled separately and attached during operation.

Testing

• 4 After assembly is completed, each device is tested using special equipment that simulates pressures in the body. All electronic components are tested with electronic test equipment to ensure the proper function of all circuitry.

Sterilization/packaging

• 5 After the artificial heart is tested and passes, it is sent to an outside service for sterilization. Each device is sealed in plastic trays and returned to the heart manufacturer. It is then packaged in custom suitcases to protect it from contamination and prevent damage.

Quality Control

Most components have already passed inspection before they arrive at the heart manufacturer. Some components are still inspected dimensionally since they require tight tolerances—on the order of millionths of an inch, which requires special measuring tools. To meet FDA regulations, every component (including adhesives) used in the process is controlled by lot and serial number so that tracking problems is possible.

Byproducts/Waste

Scrap titanium is recovered and recycled after remelting and recasting. Otherwise, little waste is produced since most components have passed inspection before leaving the various manufacturers. Other defective parts are discarded. Once a device has been used by a patient, it is sent back to the heart manufacturer for analysis to improve the design.

The Future

Within the next decade, a number of new devices will come on the market. Pennsylvania State University researchers are developing an electromechanical heart powered by radio-frequency energy that is transmitted through the skin. A motor drives push plates, which alternate in pressing against plastic blood-filled sacs to simulate pumping. Patients carry a battery pack during the day and sleep with the device plugged in to an electrical outlet. This artificial heart will be tested in humans by 2001.

Several research groups are developing pumps that circulate blood continuously, rather than using a pumping action, since these pumps are smaller and more efficient. In Australia, Micromedical Industries Limited is developing a continuous-flow rotary blood pump, which is expected to be implanted in a human by 2001. The Ohio State University's cardiology department is developing a plastic pump the size of a hockey puck that is self regulating. This pump is implanted in patients for several weeks until their own heart recovers.

Thermo Cardiosystems, Inc. is also working on a LVAD with a continuous flow rotary pump), expected to be implanted sometime in 2000, and a LVAD with a continuous flow centrifugal pump. The latter is still in an early development phase, but is planned to be the world's first bearingless pump, meaning that it won't have any parts that wear. This is accomplished by magnetically suspending the rotor of the pump. Both these devices will be available with transcutaneous energy transfer, meaning that the devices will be fully implantable.

With fewer donor hearts becoming available, others are also developing an artificial heart that is a permanent replacement. These replacements may be in the form of a left ventricle assist device or a total artificial heart, depending on the patient's physical condition. LVADs are being developed by inventor Robert Jarvik and renowned heart surgeon Michael DeBakey. Total artificial hearts are being jointly developed by the Texas Heart Institute and Abiomed, Inc. in Massachusetts. In Japan, researchers are developing total artificial hearts based on a silicone ball valve system and a centrifugal pump with a bearing system made from alumina ceramic and polyethylene components.

Alternatives to artificial hearts and heart-assist pumps are also under development. For instance, a special clamp has been invented that changes the shape of a diseased heart, which is expected to improve the pumping efficiency by up to 30%. Such a device requires minimal invasive surgery to implant.

Where to Learn More

Periodicals

Bonfield, Tim. "Device to Help Hearts." Cincinnati Enquirer (November 7, 1999).

Castor, Tasha. "Ohio State University Cardiology Unit Set to Try Heart Pump." The Lantern (May 6, 1999).

"Electric Hearts by 2005." Popular Mechanics (March 1997).

Gugliotta, Guy. "Upbeat on Man-Made Hearts: Improved Devices Save Those Too III for Transplant." The Washington Post (June 28, 1999): AOl.

Guy, T. Sloane. "Evolution and Current Status of the Total Artificial Heart: The Search Continues." ASAIO Journal (January-February 1998): 28-33.

Hall, Celia. "Thumb-Sized Pump Can Cut Heart Deaths." The Daily Telegraph (September 13, 1999): 11.

Hesman, Tina. "Pump Brings New Expectations for Artificial Heart." Omaha World-Herald (December 12, 1999).

Hopkins, Elaine. "Device Lets Heart Patient Await Transplant at Home." Journal Star (November 30, 1999).

Kinney, David. "Effective Artificial Heart Seems Within Reach." The Los Angeles Times (January 23, 2000).

Kolff, William. "Early Years of Artificial Organs at the Cleveland Clinic: Part II: Open Heart Surgery and Artificial Hearts." ASAIO Journal (May-June 1998): 123-128.

Kolff, William. "The Need for Easier Manufacturing of Artificial Hearts and Assist Devices and How This Need Can Be Met by the Vacuum Molding Technique." ASAIO Journal (January-February 1998): 12-27.

Kunzig, Robert. "The Beat Goes On." Discover (January 2000): 33-34.

M2 Communications. "Successful Blood Compatibility Tests for Micromedical's Artificial Heart." M2 PressWIRE (March 26, 1999).

Phillips, Winfred. "The Artificial Heart: History and Current Status." Journal of Biomechanical Engineering (November 1993): 555-557.

Takami, Y. et al. "Current Progress in the Development of a Totally Implantable Gyro Centrifugal Artificial Heart." ASAIO Journal (May-June 1998): 207-211.

Wilson, Steve. "A Life and Death Race Against Time. " Arizona Republic (November 14, 1999).

Yambe, T. et al. "Development of Total Artificial Heart with Economical and Durability Advantages." The International Journal of Artificial Organs (1998): 279-284.

Other

"Progress on Development of an Artificial Heart." http://www.uts.edu.au/new/archives/l999/February/02.html (December 29,2000).

—LaurelM.Sheppard

Artificial heart

The heart functions primarily as a pump to keep blood circulating through the body. Because the heart's job is so repetitive, medical researchers have long considered developing a mechanical pump to replace it. In 1935 French surgeon Alexis Carrel (1873-1944) and famed American aviator Charles Lindbergh (1902-1974) designed a perfusion pump. The perfusion pump was designed to work outside of the human body. Its job was to keep unattached organs, including the heart, alive by circulating blood through them.

Early Developments

The first completely artificial heart (called a "TAH") was implanted in 1957 in a dog at the Cleveland Clinic. Willem Kolff, a Dutch-born surgeon, and T. Akutsu perforned the surgery. Kolff later led a medical team at the University of Utah at Salt Lake City in perfecting the artificial heart. In 1964 the National Institutes of Health established an Artificial Heart Program to develop both partial and total artificial heart devices.

Michael DeBakey (1908-) designed and implanted a pneumatically-driven (worked by air pressure) component called a Left Ventricular Assist Device (LVAD) in 1966. The LVAD served the chamber of the heart that pumps blood out into the arteries. Since the majority of severe heart disease is caused by left the ventricle failure, this was a major development.

Human Experimentation

The first implantation of an artificial heart in a human being was carried out in 1969. Denton Cooley (1920-) and his surgical team at the Texas Heart Institute performed the surgery. The pneumatically driven Dacronlined plastic heart used in the procedure had been designed by Argentineborn Domingo Liotta. Implanted as a temporary measure, its goal was to keep a cardiac patient alive until a heart transplant could be performed.

It wasn't until 1982 that the first artificial heart implant intended for permanent use was made. A surgical team headed by William DeVries at the University of Utah performed the procedure. Dentist Barney Clark made worldwide headlines when he was given a second chance for life with the Jarvik-7. The Jarvik-7 was designed by American physician Robert Jarvik. The device was a pump made of plastic and titanium powered by compressed air. The compressed air was delivered by a large external (outside) air compressor through two tubes that passed into the body via incisions in the abdomen. Clark survived the surgery for only 112 days.

DeVries then joined the staff at Humana Hospital in Louisville, Kentucky. At Humana he carried out four other Jarvik-7 implants during 1984 and 1985. Each of these patients also died, including William Schroeder. Schroeder survived 620 days, but suffered a long series of debilitating setbacks during that period. The results of actual permanent implantation of the Jarvik-7 revealed its limitations, including the fact that it caused blood clots to form that traveled to the brain and caused strokes.

Current research focuses on a new generation of electrically-powered artificial hearts. These devices use portable battery packs to transmit power via radio signals. The radio signals pass through unbroken skin to an implanted mechanical heart pump. This provides the patient with mobility and eliminates the need for permanent artificial openings in the body. It also reduces the possibility of infection, a problem that existed with the first air-powered heart. The first of these electric devices was experimentally implanted in a human subject in 1991.

[See also Barnard, Christiaan ; Transplant, surgical ]

heart, artificial Since the 1960s there have been many attempts to develop implantable pumps to replace the function of the heart. These were initially evaluated in animals. Only in the past few years have the newer designs, refined in the light of experimental findings in animal trials, been used with reasonable success in humans. Improved materials as well as advances in electronics and mechanical engineering have also played a major part in making the artificial heart sufficiently safe and effective to allow limited clinical application.

In principle, the device consists of a rigid chamber, made of an inert material such as titanium, usually of hemispherical shape and about 7–8 cm in diameter, within which there is a moving polyurethane diaphragm which evacuates the contained blood. An inlet and an outlet valve ensure flow in one direction. Early models used an external pump to pneumatically displace the moving diaphragm. Recent designs have miniaturized electrical motors activating a pusher plate within the device, but connected to externally carried batteries by wire, or by a transcutaneous electrical energy transfer system. As the devices are not linked to any of the normal influences in the body which naturally control the output of the heart, there have to be control systems which modify the artificial pump's output and regulate the pressure of the blood flowing into the device.

Most causes of heart failure, for which use of an artificial device might be contemplated, affect the left ventricular pumping chamber. It is therefore possible to use a mechanical pump which takes its input of blood from the diseased left ventricle and returns the blood at appropriate pressure to the aorta — thus acting as a left ventricular assist device. It is this form of device which is presently showing most clinical success and has widest application.

For patients with both left and right ventricular failure, devices are available which have two parallel pumping chambers. This device is a true ‘artificial heart’, and is a mechanical alternative to a heart transplant.

The problems associated with artificial devices used to replace the heart are considerable. Clotting of blood within the device is a risk. Clots can immobilize the artificial valves and interfere with the pump itself, or can detach from the device to travel in the bloodstream. This results in clinical effects which depend on where the clot goes. If a clot enters the circulation of the brain the result is often a stroke. Anticoagulant drugs are required to minimize this risk, and anticoagulation itself carries risks of bleeding. Also, there is the risk of infection developing in the device; mechanical devices are liable to damage the blood, causing rupture of red cells and a risk of kidney damage due to the released haemoglobin from the red cells; and there is a need for regular changes of battery power source.

At present left heart assist devices will allow relatively normal life for many months, reversing many of the adverse effects on the body of long-standing heart failure. Most clinical use has been as a ‘bridge to transplant’, enabling ill patients to survive until a suitable heart becomes available for transplantation. Occasionally, use of a left heart assist device has been temporary, where the heart has been affected by a condition which is recoverable.

At present, the technology of artificial hearts is advancing rapidly, but the devices currently in use are not as satisfactory as the transplanted human heart.

D. J. Wheatley

artificial heart (ar-ti-fish-ăl) n. a titanium pump that is implanted into the body to take over the function of a failing left ventricle in patients with heart disease. This allows the diseased ventricle time to recover its function. The pump is powered by an external battery, strapped to the patient's body, to which it is connected by wires passed through the patient's skin. The most recent devices are small enough to fit into the heart itself.