The Invention of the Artificial Heart

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The Invention of the Artificial Heart

Overview

During the second half of the twentieth century coronary heart disease became the leading cause of death in wealthy, industrialized nations. Moreover, more than half of the deaths in the United States were caused by cardiovascular diseases. Many of these deaths could have been prevented by aggressive management and surgical procedures, including heart transplant operations. The shortage of donor hearts, however, led to hope that a totally implantable mechanical device could overcome the shortage and avoid the problem of immunological rejection, but early attempts to implant permanent artificial hearts were criticized as premature human experiments. Indeed, the controversies raised by experimental implantations in the 1960s may have inhibited the development of a permanent heart replacement. The poor quality of life provided by artificial hearts instead led to efforts to develop a new generation of left ventricular assist devices.

Background

The human heart is a remarkable organ—little bigger than a fist—that beats over 100,000 times a day without rest. In an average adult, the heart pumps more than 4,300 gallons (16,000 liters) of blood a day through nearly 100,000 miles (161,000 km) of blood vessels. Picturing the heart as just a pump, Michael E. DeBakey, a pioneer of heart surgery, who has been called the "Texas Tornado," predicted that a mechanical device could duplicate its main function. Artificial hearts actually date back to 1957, when Willem Kolff, inventor of the artificial kidney, and Tetsuzo Akutsu implanted an experimental heart into animals. Kolff's model heart kept a dog alive for 36 hours. Heart specialists and scientists have pursued four general approaches to heart replacement: artificial hearts, transplantation of donor hearts, assist devices that replace just part of the natural heart, and replacement hearts developed by tissue-engineering techniques in the laboratory, or hearts grown in genetically altered animals.

The ideal artificial heart would function essentially maintenance free for many years within the hot, humid, corrosive internal environment of the body. The design of a successful artificial heart would have to overcome the difficulties that have been revealed since the first such devices were tested in the 1960s: damage to the blood caused by contact with artificial materials, rejection of the replacement heart by the body's immune system, difficulties in delivering adequate power to the pump without connections through the skin, miniaturizing the pumps enough for use in children and small adults, and adjusting blood flow in response to physiological stress. Although the artificial hearts in development during the 1990s may solve many of these problems, these devices will probably not become practical or routine for many years. Indeed, the history of the artificial heart is a history of controversial cases.

Impact

Studies conducted by the Institute of Medicine in the 1990s estimated that 10,000 to 20,000 Americans per year could be candidates for a total artificial heart and another 25,000 to 50,000 might need a left ventricular assist device. Heart failure affects about 5 million Americans per year; in addition, mortality from heart failure increased threefold between 1974 and 1994. Various forms of artificial pumps have provided temporary "bridges," keeping patients alive while awaiting a transplant, but the number of donated hearts is only about 2,000 per year. For many patients, assist pumps, also known as left ventricular assist devices (LVAD), may be more practical than replacing the entire heart. DeBakey began working on an artificial heart and related devices in 1960. He invented a simple blood pump, the LVAD, that could assist the heart while a patient waited for a transplant. In 1966 DeBakey performed the first human implantation of an LVAD.

One of the most dramatic events in twentieth-century surgery occurred in 1967, when Christiaan Barnard (1922- ), a South African surgeon, performed the first human heart transplant. (In many cases, heart disease may be so severe that a patient may not survive the wait for a donor heart.) Attempts to use animal organs, such as Leonard Bailey's 1984 transplantation of a baboon's heart into a newborn, who was identified as Baby Fae, ended in failure. Therefore, the shortage of donor organs provided a great impetus to the development of an artificial heart.

On April 4, 1969, Denton A. Cooley performed the first human implantation of a total artificial heart when he used a device developed by Domingo Liotta to sustain the life of Haskell Karp. Karp was a 47-year-old patient who was in cardiac failure after surgery for a left ventricular aneurysm. Karp lived with the artificial heart in his chest for 65 hours but died shortly after receiving a heart transplant. DeBakey claimed that the heart Cooley used was identical to one under development in his laboratory and that Cooley had used it without permission. Because the device had been used with only limited success in calves, DeBakey considered human implantation premature and unwise. Although Cooley had obtained consent for the operation from the patient, he had not sought permission from the hospital review board or from federal agencies. He and Liotta thought that permission would not have been granted and that they would have lost a perfect opportunity to perform the experiment. The working relationship between Cooley and DeBakey was destroyed by the controversy surrounded the Karp operation.

Then Karp's widow brought a wrongful death suit against Cooley. She claimed that she and her husband had not been fully informed of the risks of the experimental procedure. The judge dismissed the case, ruling that the patient had given informed consent and that the hospital and surgeons had thoroughly informed the patient of the risks of the procedure and the low probability of complete recovery or survival. The decision in this case is regarded as a landmark in the development and implementation of medical technology.

In 1981 Cooley performed another controversial operation, the implantation of a total artificial heart developed by Tetsuzo Akutsu. The 36-year-old patient was sustained on the artificial heart for 55 hours until a donor heart was available for transplantation. Robert Jarvik, a physician and biomedical engineer, approached DeBakey about testing a similar device, known as the Jarvik-7, but DeBakey refused because he did not think that the device was ready for human use. One year later, William DeVries, in cooperation with Jarvik, implanted the Jarvik-7 heart into the chest of Barney Clark, a 61-year-old Seattle dentist dying of heart failure.

In contrast to the Karp case, in which the artificial heart was implanted as a bridge to transplant, DeVries and Jarvik intended to use their artificial heart as a permanent replacement for the diseased heart. Clark, who survived for 112 days on the artificial heart, was honored by members of the implant team as a "true pioneer" who understood that he was participating in an experiment that was unlikely to save his life but one that would provide information to help biomedical science and other patients.

Five similar implants were performed through 1985. The longest survivor was William Schroeder, who was supported by the Jarvik-7 for 620 days. The spectacle of the poor quality of life and painful complications endured by patients such as Clark and Schroeder created a significant public backlash against the artificial heart. Moreover, many doctors, scientists, ethicists, and policy makers concluded that use of the artificial heart was premature and that it would be well into the next century before a new generation of artificial hearts significantly improved patients' lives. The problems associated with implantable artificial hearts eventually led to a general consensus that an assist device would be more practical and beneficial to patients. The original purpose of LVADs was to keep people with terminal heart failure alive until a donor heart became available. In this manner, the Jarvik-7 was later used in hundreds of patients as a bridge to transplantation.

By the early 1990s, sophisticated LVADs were being used routinely in hospitals all over the world. Many of the early devices, however, were too large for use in children and small adults. Researchers thus focused on the development of a small, but still powerful LVAD. DeBakey and others had to carry out some of their experiments and clinical trials in Europe because governmental rules regarding clinical trials were more stringent in the United States. Innovative solutions to the problem of creating a better pump grew out of a collaboration between DeBakey and National Aeronautics and Space Administration (NASA) scientists. (This collaboration came about following an operation that DeBakey had performed on David Saussier, a NASA engineer.

The DeBakey Ventricular Assist Device (VAD), a miniaturized pump approximately one-tenth the size of the older devices, caused less damage to blood cells, required less than eight watts of power, and could be recharged through the skin. Many other experimental devices were also undergoing testing by 1998, when the 90-year-old DeBakey went to Germany to supervise the first human trials of his VAD personally. Six patients in all, the first, who was in critical condition at the time of the operation, died six weeks later. The second had his device removed because of the formation of a blood clot in the mechanism, but two other patients were able to leave the hospital with the device still in place.

The new generation of LVADs offers hope to many patients because of an unexpected phenomenon reported by several heart transplant centers. Some of the patients using LVADS while waiting for a donor heart were actually recovering. Apparently, the complete rest to the left ventricle provided by the LVAD reversed heart failure to a significant extent and enlarged heart cells were returning to normal size. Therefore, LVADs might also be used as a "bridge to recovery."

In addition to human heart transplants and mechanical hearts, some scientists think that animal tissues and organs or combinations of living cells with artificial materials will eventually be used to assist or replace ailing hearts. Scientists are now trying to grow heart muscle tissue, heart valves, and blood vessels in the laboratory; this approach is known as tissue engineering. Because an entire heart rarely fails, helping many patients with tissue-engineered heart muscle may be possible. In addition, in the field called xeno-transplantation, scientists are already looking at ways to change animal organs so that they will not be rejected by human recipients. Opposition from animal activists and the threat of previously unrecognized viruses has made primates less desirable as sources of organs, but transgenic pigs may eventually provide organs for humans. Other scientists, however, believe that much of the social and individual burden of heart disease could be prevented through exercise, changes in diet, and the elimination of smoking.

LOIS N. MAGNER