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M. Dilek Avşaroğlu, 2002
1. INTRODUCTION....................................................................................................................................... 3
2. HEART FUNCTION................................................................................................................................. 5
3. HISTORY..................................................................................................................................................... 6
4. MATERIALS.............................................................................................................................................. 9
5. RECENT DEVELOPMENTS............................................................................................................... 10
5.1. Ventricular Assist Devices (VADs)........................................................................................... 10
5.1.a. Jarvik-2000 Heart............................................................................................................................. 10
5.1.b. HeartMate Left Ventricular Assist Devices................................................................................... 11
5.2. Total Artificial Hearts................................................................................................................ 12
5.2.a. AbioCor Total Artificial Heart........................................................................................................ 12
5.2.b. CardioWest Total Artificial Heart.................................................................................................. 14
6. CONCLUSION.......................................................................................................................................... 15
7. REFERENCES........................................................................................................................................ 16
8. WEB SITES.............................................................................................................................................. 16
In spite of the efforts made in prevention and in reducing the risk factors for mortalities linked to cardiopathies, heart disease continues to be the main cause of death in countries with high socioeconomic development. There is a human die from heart failure every 33 seconds. To rescue the end-stage heart failure patients, one has to be either transplanted or implanted.
Transplantation: Transplantation of a donor heart involves the total replacement of the failed heart with another natural heart, which is acceptable for the body of the patient.
Implantation: Implantation with an artificial heart involves the total replacement of the patients’ own heart, which is failed, with a man-made heart.
There is another approach for end-stage heart failure patients called bridge-to-transplantation. It is a short-term implantation followed by transplantation. It involves ventricular assist devices.
Although it seems to be good to transplant the patients, there are some limitations for transplantation:
1. Number of patients suffering from heart failure is very high.
2. Donor heart number is very smaller than it is needed.
3. The reason of this shortage is that, donations are few and also the donated hearts are not always found alive.
4. The natural defence mechanisms of all living organisms reject foreign matter and in particular foreign proteins.
5. The high assurance of success is about 90% from identical twin to identical twin and it is decreased between non-related donors to 25%.
6. In some cases, heart disease may be so severe that the patient may not survive the wait for a donor heart.
For these reasons, there is a big gap in the cardiac surgery and the desire to fill that gap has led the scientists to investigate mechanical solutions for pumping blood. Due to the progress in both high technology and cardiac surgery leads several types of artificial organs in cardiovascular field. From artificial heart valves to a total artificial heart, there are several types of artificial organs advanced in cardiac surgery. Table 1 shows the advances in cardiac surgery.
Table 1. Advances in cardiac surgery (Ref.10)
Artificial organs Cardiac surgery Other technologies
Cardiopulmonary bypass Congenital heart disease Polymer chemistry
Oxygenator Mechanical engineering
Vascular prosthesis Valvular disease Electric engineering
Cardiac pacemaker System engineering
Artificial valve Ischemic heart disease Information engineering
Assisted circulation (Angina, myocardial infarction) Patho-physiology
Ventricular assist device Immunobiology
Total artificial heart Heart transplantation Molecular biology
Genetic engineering
Artificial heart
(VAD total artificial heart)
The limitation for the uses of artificial hearts are ethical believes. For many people, the heart is thought to be the house of feelings, the house of soul and the house of God. These people reject the implantation and for this reasons the human trials of artificial hearts is limited.
To understand the artificial heart, first, one must know the actual mechanism of the natural heart.
The normal heart is a strong, muscular pump a little larger than a fist. It pumps blood continuously through the circulatory system. Each day the average heart "beats" (expands and contracts) 100,000 times and pumps about 2,000 gallons of blood. In a 70-year lifetime, an average human heart beats more than 2.5 billion times.
The heart acts as four interrelated pumps. The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava. It pumps the deoxygenated blood through the tricuspid valve to the right ventricle. The right ventricle pumps the blood past the pulmonary valve through the pulmonary artery to the lungs, where it is oxygenated. The left atrium receives the oxygenated blood from the lungs through four pulmonary veins and pumps it to the left ventricle past the mitral valve. The left ventricle pumps the blood to all areas of the body via the aortic valve and the aorta.
The heart's constant contracting and relaxing forces blood into the arteries. Limited relaxation or dilation follows each contraction. Cardiac muscle never completely relaxes: It always maintains a degree of tone. Contraction of the heart is called systole or "the period of work." Relaxation of the heart is called diastole or "the period of rest." A complete cardiac cycle is the time from onset of one contraction, or heart beat, to the onset of the next.
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Figure 1. Schematic diagram of heart (Ref. ii)
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The first appearance of artificial heart dates back to 1812, when a French physiologist, Le Gallois, suggested the possibility to maintain organ function outside the body by an artificial arterial pump. He worked with rabbits, but he failed to prove his hypothesis. Of course, it did not mean that he was not attracted any attention.
After Le Galois, two scientists, Frey and Gruber, worked on the topic and by designing an oxygenator and a heart-lung machine respectively they took their place in the historical scenario of mechanical circulatory support systems in 1884. Their oxygenator was a film-oxygenator and used for the first 10-15 years of open-heart surgery.
Besides film-oxygenators, Schröder started his work on bubble-oxygenator in 1882 that was used in 1960s-70s instead of film oxygenators. The observation of bubbling out blood was belonging to Brown-Sequard in 1850s.
Another important work on heart-lung machines was belonging to John Gibbon, who in 1937 published his experiments done on cats. The interest of his work is the details that he considered in that early days still accurate today. His design was mainly included a piston-type pump. Beside these pumps, direct bar compression pumps had been used in initial studies. Later, the roller pumps took place and De Bakey designed a roller-pump (Figure 2) based heart-lung machine in 1934. Mainly, heart-lung machine pumping mechanisms did not undergo hardly any major changes after that.
Figure 2. Principle of the roller pump (Ref.6)
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Roller pump has a motor-operated wheel, which is surrounded by free-turning rollers. The blood-handling portion is a tube that is easily sterilized. This design allows pulsatile flow as natural heart and the pumped volume can be controlled according to the motor speed. The main disadvantage of the roller pump is freely rotating rollers produce shear forces that damage the blood cells.
In 1954, the father of artificial kidney, William Kolff observed blood oxygenation through a membrane. In 1965, the first membrane system, the Brahmson lung, became available for routine open-heart surgery. The change through membrane system to hollow-fibers occurred, due to its simpler pump technique. Today, the use of capillary membrane oxygenators is standard worldwide.
Clarence Dennis did the first real clinical application of a heart-lung machine in 1951, but it was not successful and the patient died. The first open-heart surgery was done in 1954 by heart-lung machine both Ake Sennings’ and Gibbons’ respectively. Due to volume and control mechanism of heart-lung machines, it was not applicable for babies. In 1970, Turma took the initiative role to design a special pump oxygenator for infants. Today, it is accustomed to having reliable heart-lung machines for all ages.
Currently, off-pump bypass procedures are chosen in coronary surgeries. As early as 1958, it was Senning again who performed stip-graft technique which is quite similar to off-pump coronary surgery.
Up to here, non-of the techniques developed did not require the replacement of heart with a mechanical pump. The first idea of replacement of heart with mechanical pump came to two minds, Gibbs in US and Demigod in Russia, before the World War II. In 1957, Akutzu and Kolff successfully implanted an air-driven artificial heart (Figure 3) made polyvinyl chloride in a dog sustained for 90 minutes.
Figure 3. Air-driven artificial heart (Ref. vi)
The design involved basically two pumps, one for each side of the heart. It was made out polyvinyl chloride and a flexible sac inside.
Besides Kolffs’ group, Mike De Bakey had artificial heart program in US too. De Bakey, in 1966 used a pneumatically driven left ventricular assist device. In 1969, Cooley made the first human implantation of a total artificial heart that was designed by Liotta in orthotopic position (Figure 4).
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Figure 4. Liotta’s artificial heart (Ref. vi)
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This 1969 heart, designed by Dr. Domingo Liotta, was the first to be implanted in a human being as a bridge to transplant by Dr. Denton A. Cooley. The patient survived for almost three days with the artificial heart and 36 hours more with a transplanted heart.
In 1964 National Heart Institute (NHI) in US started an artificial heart program under the guidance of Frank Hastings. Than the program grew with different concepts for artificial hearts. Finally Jarvik-7 (Figure 5) had the approval of an artificial heart by FDA and implanted on December 1st 1982. The patient had lived for 112 days.
Figure 5. Jarvik-7 artificial heart (Ref. iii)
Robert Jarvik designed it. It had two pumps, each with disk-shaped mechanism. It was driven externally and made of aluminum and Dacron.
Researches in Europe about total artificial heart were done too. In 1962, the heart of a dog was replaced successfully by Büchlers’ group in Berlin. In Vienna Navrotil started a program still active today under the guidance of Ernst Walner. In Aachen, “artificial organ” project was started, but this was mainly about ventrical assist devices; Medos, pneumatically driven assist ventricals are the examples.
After 1985, experiments on permanent and definite replacement of heart with a mechanical pump were increased. There are several types of pumps and ventrical devices commercially available.
Nowadays, the most frequently implanted pulsatile device is the Novacor heart, an electromechanically driven ventrical. The Abiomed total artificial heart called “Abiocor” is the latest example of total artificial heart replacement. It was implanted in July 2001, but the patient died on November. Abiocor heart is the first total artificial heart that allows movement of the patient.
Metals, polymers, and ceramics have been used in cardiac surgery in a variety of applications: heart valves, valve rings, vascular grafts, indwelling catheters, arterial and ventricular patches, sutures, heart-lung machines, and various circulatory assist devices such as intraaortic balloon pumps, left ventricular assist devices, and total artificial hearts. Many early attempts to assist or replace various cardiac structures with man-made materials failed as a result of shortcomings in the material or the design. However, these early failures informed development of better man-made materials and designs, and now metals, polymers and ceramics can be used in cardiac devices over the long term with minimal adverse tissue reaction.
In the current clinical application of circulatory assist devices, the major problem areas are design, e.g. anatomical fitting; biomaterial, e.g. pannus ingrowth over valves, calcification of the blood sacs, or thrombic complications; or medical, e.g. device centered infections. Furthermore, because circulatory assist devices are in contact with both blood and thoracic or abdominal soft tissue, the soft tissue response to the housing material is also important. The interactive effects of design and choice of materials on hemocompatibility and durability are also important factors. Elements of pump design, such as flow patterns, stroke volumes, and durability deeply affect the thrombogenicity and hemolysis of various pump components.
Various materials are used in the manufacture of the artificial hearts, but mainly polymers are used. The polymer of choice for the pump conduits is low-porosity, woven or knitted DacronÒ, with an established intrathoracic and intraabdominal biocompatibility. DacronÒ is the trade name (DuPont) for the linear aromatic polyester, polyethylene tetraphthalate. It is a thermoplastic polymer and can lose its structural integrity when exposed to heat. It is manufactured in knitted, woven or velour cloth.
Polyurethanes are also used most frequently, because of their durability, flexlife and hemocompatibility. Polyurethanes are made by polymerizing monomers that contain a urethane group. BiomerÒ, AvcothaneÒ, CardiothaneÒ, TecoflexÒ, PellethaneÒ, AngioflexÒ are the examples for the polyurethanes used in the components of total artificial heart and ventricular assist devices. Polyurethane surfaces have been modified in an attempt to increase their hemocompatibility, e.g. incorporating biocompatible layers into the surface, depositing heparin, protein or cell layers onto the surface, and adding texture to the surface.
Polymers in rigid forms are used for pump housing for example Epoxy and Polysulfone. For the same purpose, metals are also used especially the
Titanium alloys. Titanium has superior mechanical properties and corrosion resistant. It may either commercially pure or alloyed, usually as the Ti-6A1-4V alloy. The thin, chemically inert oxide film that forms on its surfaces makes the metal or its alloys perfectly biocompatible. In addition, the electronegativity of the film improves its hemocompatibility and, thus, renders it suitable for cardiovascular applications.
VADs assist the pumping on the ventricles either left or right or both (biventricular). Most patients are dying of left heart failure. When the heart is unable to pump blood to the head, kidney, arms and legs, it is found the muscle can be replaced best by leaving the heart in place and putting in an assist device that can perform this role of the heart, without having to remove the heart.
An example of this technology is Jarvik-2000 Heart. It is an electrically powered; axial-flow left ventricular assist device. It is small, weighs 90 g, measures 2,5 cm in diameter and displaces 25 ml; it is quiet and easy to implant.
Figure 6. Jarvik-2000 (Ref.4)
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The pump shell is titanium and the blood-contacting surfaces are also titanium. Power is transmitted by a bundle of extrusion blood pump, enclosed within a silicone tube. Lithium-ion or sealed lead-acid batteries power the pump, which is placed externally and fixed on a belt.
There are two other variants of Jarvik-2000 heart. Totally implantable version has a different controller and power system. A redundant dual-coil motor powers its blood pump. The microprocessor based controller responds to the cardiac cycle by sensing changes in the motor current, which correspond to changes in the pump differential pressure. The third version differs from the original version in its method of transferring external power and control. The power cable is brought out through the back of the head with a connector attached to the base of the skull. The external power cable is connected to a titanium pedestal that is screwed to the skull.
The clinical results of Jarvik-2000 implantation have been encouraging, as the pump has led to rapid recovery and stabilization of clinically ill patients. The role of this pump will be further clarified by larger clinical trials. Meanwhile, its long-term use appears to be feasible and safe.
The HeartMate family of implanted left ventricular assist devices was developed by Thermo Cardiosystems, Inc. (TCI). The company places it great emphasis on the durability and reliability of the device. TCI uses space age materials such as titanium alloys and Cardioflex polyurethane plastics as well as advanced fabrication technology to make all HeartMate devices. For blood compatible surfaces, to reduce the incidence of clot formation and thromboembolism, the blood-contacting surfaces are encouraged the deposition of a living lining derived from the patients’ own blood.
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There are three versions of HeartMate family. HeartMate I is a pulsatile diaphragm pump available as either an implanted pneumatic or a vented electric device. HeartMate II is an axial-flow rotary pump utilising blood immersed mechanical bearings with textured blood contacting surfaces. It has either percutaneous or transcutaneous versions. HeartMate III (Figure 7) is a centrifugal-flow rotary pump with a magnetically levitated impeller to eliminate any mechanical bearings. It is a continuous flow device with either percutaneous or transcutaneous versions as HeartMate II.
5.2. Total Artificial Hearts
The action of the artificial heart is entirely similar to the action of the natural heart. There is, however, one huge difference: the natural heart is living muscle, while the artificial heart is plastic, aluminum, and Dacron polyester. As a result, the artificial heart needs some external source of "life." An external power system energizes and regulates the pump through a system of compressed air hoses that enter the heart through the chest. The early example of an artificial heart is Jarvik-7 as mentioned previously. Since then, development of an improved artificial heart has continued. One possibility is an electrical heart powered by a small wearable battery that does not require any break in the skin. Perhaps, someday, the artificial heart will become a realistic, permanent option for survival.
The AbioCor system is an exciting alternative to VADs. There are patients who have failure on both left and right side of heart, or who have other problems that limit the use of LVADs. In that setting we had no choice but to let the patient die. There is now for the first time a totally implantable artificial heart that could potentially allow us to implant a device that allows patients to live for a long period of time. This is a new, well-designed device. It is designed by AbioMed, Inc.
It is the latest approach in the total artificial heart area. FDA approval was given in January 2001 and first implantation achieved in July 2001. The AbioCor is an advanced system that has been design to fully sustain the bodys’ circulatory system.
AbioCor is primarily made of titanium and AngioflexÒ. AngioflexÒ is proprietory of AbioMed and it is polyether based polyurethane plastic. It is flexible and durable. The moving parts of the AbioCor such as valves and ventricular membranes made out of AngioflexÒ.
Unlike any of its precursors, AbioCor is designed to fit inside the body and without skin penetration to an external device, so that a patient can remain movement.
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Figure 8. AbioCor heart (Ref. iv)
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Figure 9. AbioCor heart (Ref. iv)
The AbioCor heart consist of:
Ø An internal thoracic unit, which has two artificial ventricles with valves and a motor driven hydraulic pumping system.
Ø An internal rechargeable battery, which is for emergency use. These batteries are kept charged by the external battery. It has the capacity of 6-8 hours.
Ø An external battery that is fixed on the belt. Both external and internal batteries are lithium-ion batteries.
Ø An internal electronics package that monitors and controls the system performance including the pumping speed of the heart based on the physiological demand of the patient.
Ø A TET (transcutaneous energy transmitter) device that transmits energy through the skin achieves power transfer.
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Figure 10. CardioWest total artificial heart (Ref.1)
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The CardioWest total artificial heart (TAH) is the descendant of the Jarvik-7. It is a pneumatic device that is used as a bridge-to-heart transplantation and it involves the total replacement of the failing ventricles. The prosthetic ventricles are made of polyurethane and Medtronic-Hall mechanical valves that provide unidirectional flow. Blood and air are separated by a four layer, segmented polyurethane diaphragm that retracts during diastole and is displaced forward by compressed air propelling blood out of the prosthetic ventricle. The TAH can provide flows up to 10 L/min.
In conclusion, progress in the various fields of science which have promoted the development of the artificial heart has made it possible to develop devices that can fully carry out the function of the natural heart and make significant progress toward the extension of survival. By making developments toward the clinical application of artificial hearts or VADs, it will be able to make some contributions to the progress in the field of cardiac surgery.
The future will belong in large part to those technologies that are less expensive, have improved ergonomics, are simpler in surgical application, and can demonstrate efficacy levels that are an improvement over today’s approved devices. To give an idea about current market, VAD total sales are about $149 millions with 24% growth. The future profile of VADs is of lighter and smaller device, approximately one tenth of current pulsatile devices. Future devices will have reduced levels of noise and vibration, making them less noticeable to the patient and family.
The market for long-term mechanical circulatory support is currently limited to bridge-to-transplantation, with increasing competition. More favourable economics for the manufacturer depend on improved out-comes, objective data, heart failure cardiologist buy-in, expanded indications, and improved reimbursement, not only for approved therapy, but also during clinical trials. If these are achieved, there still is a very attractive business potential.
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2. Coepland, J. G.; Mechanical assist device; my choice: the CardioWest total artificial heart. Transplantation Proceeding/ Vol: 32/ Issue: 7/1523-1524/ November 2000
3. Dallas, W. A.; Blood pumps: technologies and markets in transformation. Artificial Organs/ Vol: 25(5)/ 406-410/ 2001
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5. Greco, R. S.; Implantation Biology. CRC Press 1994 USA
6. Mayers & Pardonnet; Engineering in the heart and blood vessels. Wiley-Interscience 1969 USA
7. Messmer, B. J.; From heart-lung machine to the total artificial heart. The International Journal of Artificial Organs/ Vol: 24/ no: 2,2001/ 63-69
8. Pellegrini, A.; Mechanical circulation-assist as a bridge to heart transplant. Leadership Medica/ December 1998
9. Portner, M. P.; Economics of devices. Ann. Thoracic Surgery/ Vol: 71: S199-201/ 2001
10. Sezai, Y.; Progress and future perspective in mechanical circulatory support. Artificial Organs/ Vol: 25(5)/ 318-22/ 2001
11. Timothy R. M.; HeartMate left ventricular assist devices: a multigeneration of implanted blood pumps. Artificial Organs/ Vol: 25(5)/ 422-426/ 2001
i. http://www.abiomed.com
ii. http://www.tpub.com/corpsman/22.htm
iii. http://www.150.si.edu/150trav/remember/r817.htm
iv. http://www.heartpioneers.com
v. http://www.whitaker.org
vi. http://www.abiomed.com/prodtech/abiocor/evolution.html
vii. http://www.americanheart.org
