A C&EN Feature
Part 2
Artificial organs Total artificial hearts and heart-assist devices
Howard J. Sanders Senior Associate Editor Washington, D.C.
Before we discuss artificial heart devices, we should know something about the function and structure of the natural heart. Quite simply, the function of the heart is to pump blood. Part of this pumping is needed to send blood to the lungs. The remainder of the pumping is required to send oxygenated blood from the lungs to the rest of the body—including the heart muscle itself, to enable the heart to function as a living organ. Human hearts have four chambers: the right and left atriums (auricles) and, directly below them, the right and left ventricles. The atriums act as reservoirs and as pumps that rhythmically, through valves, force blood into the ventricles. Beating simultaneously, the ventricles do the heart's main pumping. Of the two ventricles, the left one does by far the greater pumping. Its work load is about four times that of the right ventricle. The reason is that, whereas the right ventricle pumps blood only to the lungs, the left ventricle pumps blood, via the aorta, to the rest of the body. It should also be pointed out that the left ventricle has the dubious distinction of being the heart chamber most often damaged by a heart attack. Total hearts vs. assist devices. In recent years, scientists have developed
This is Part 2 of a two-part feature. was published in last week's issue. 68
C&EN APRIL 12, 1971
Part 1
more than 45 different models of artificial blood pumps. These pumps fall into two broad categories: • Total artificial hearts, which are implanted in the body after the complete natural heart has been removed. These artificial hearts are designed to perform all the functions of the living heart. • Heart-assist devices, which are completely or partially implanted in the body and take over part of the pumping action of the natural heart. The patient's living heart is not removed. In fact, the assist device is generally thought of as a temporary unit used for several days or weeks to allow the patient's living heart to work less strenuously while it repairs itself following a heart attack, heart surgery, acute myocarditis (inflammation of the heart muscle), or other problem. On the other hand, if the damaged heart cannot recover adequately after an extended period of time, a heart-assist device might be used permanently. As one physician explains, "In a real sense, a heart-assist device buys time. It allows the patient to live long enough so that his defective heart, working under a reduced load, has time to form the necessary new tissue and thus repair the reversible damage done to it. Even if the heart cannot heal itself satisfactorily, the assist device can be extremely useful in sustaining the patient until a living heart transplant becomes available:" Until fairly recently, the Artificial Heart Program of the National Heart and Lung Institute was instructed by NIH officials to place its main stress on developing heart-assist devices, rather than total artificial hearts. This approach, it was argued, was . much more logical. The rationale was
that you start with the relatively simple problems, solve them, and then go on to solve the more complex problems, using the knowledge amassed in the earlier work. Because of this decision, government-supported research on a total artificial heart (a device obviously more complex than an assist unit) was given decidedly less attention than research on heartassist devices. In recent years, many scientists have argued persuasively that work on both types of devices should be pursued with equal vigor simultaneously. Only in this way, they say, will a successful total artificial heart be developed at the earliest possible date. Actually, the Artificial Heart Program has shifted its policy in this matter and is now giving greater support to research on the total artificial heart. Heart-assist devices. Heart-assist devices are clearly an urgent need. NIH estimattes that today, for every patient who would benefit from a total artificial heart, at least 10 patients would be significantly helped by a heartassist device. In almost all cases, an assist device is designed to augment the pumping action of the heart's defective left ventricle. As we have seen, the left ventricle carries most of the pumping load of the heart and is much more likely to be injured by a heart attack than is the right ventricle. Heart-assist devices can serve a number of important functions. They can: • Reduce the work load of the heart and thus facilitate its repair. • Increase the blood flow to the heart's own tissue and thus promote the repair of reversible heart damage caused by a heart attack. • Prevent further injury to the heart that may be caused by an insufficient
flow of blood to the heart muscle following a heart attack. • Increase the blood flow to other organs of the body that might be seriously damaged by poor blood circulation following such an attack. Heart-assist devices (sometimes referred to as auxiliary blood pumps or booster pumps) come in a variety of basic types, depending on whether they are connected to the heart and the aorta, or to the heart and a femoral artery, or to the aorta only, or to neither the heart nor the aorta. These types are usually named after the physician and sometimes also the company that played the most conspicuous role in developing them, although, in some cases, at least 40 other people and several other companies were also involved in the development. Sometimes, various heart-assist devices are also described on the basis of the way in which blood flows through them—either in series or in parallel with normal blood flow. DeBakey device (1963 version). For about 10 years, Dr. Michael E. DeBakey, Dr. C. William Hall (now at Southwest Research Institute), Dr. Domingo Liotta (now at Texas Heart Institute), and coworkers at Baylor college of medicine have done extensive research on heart-assist devices, as well as total artificial hearts. Since 1964, the Baylor scientists have been assisted in this effort by scientists and engineers at Rice University. One of the heart-assist devices developed by the Baylor group was implanted in a patient in 1963. A quite different heart-assist unit developed by the Baylor-Rice team was used in seven patients between 1966 and 1968. The earlier model was implanted by Dr. E. Stanley Crawford, assisted by Dr. Hall and Dr. Liotta, on July 19, 1963, in a 42-year-old man at Houston's Methodist Hospital. Previously, the man, a private patient of Dr. Crawford, had had his defective aortic valve (the valve controlling blood flow between the left ventricle and the aorta) replaced by an artificial valve. After the operation, the patient showed signs that he would not recover from the heart-valve surgery unless his heart's pumping action was greatly augmented. At Dr. DeBakey's recommendation, Dr. Crawford implanted in the patient a type of heart-assist pump de-
The human heart
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Pulmonary vein >
Aortic arch Ascending// aorta/ill Right atrium
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Pulmonary =--^ vein
Tricusoid valve I e>ft
Pulmonary valve
^Descendinc kW aorta w I
Aortic valve
Inferior vena cava Right ventricle
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Mitral valve
Left ventricle
Myocardium _ Aoex
veloped by Dr. DeBakey, Dr. Hall, and coworkers and previously tested in dogs. The device was connected between the patient's left atrium and his descending aorta (the aorta, as it leaves the heart, first rises to a peak called the aortic arch and then descends). The pump, which one writer described as looking like a small banana, consisted of a rigid tubular housing made of Dacron-reinforced Silastic silicone rubber and, inside of it, a flexible Silastic tube, with a valve located at both ends. Pulses of pressurized air from an external source, injected between the housing and the flexible tube, alternately expanded and contracted the tube. Since blood from the left atrium
flowed inside the tube, these rhythmic pulsations pumped the blood into the descending aorta and, from there, into the general circulation. With this device fully implanted in his chest, the patient survived three and a half days. Although the operation was clearly a surgical landmark, being the first implanting of a heartassist device in a human, tests performed both during and after the operation showed that the pump definitely needed to be improved. Among other things, it caused excessive blood clotting and considerable damage to the red blood cells and other blood components. Also, the surgery required to implant the entire device was fairly complex. APRIL 12, 1971 C&EN 69
DeBakey device (1966 version). After three years of additional research, supported mainly by the Government, the Baylor group, aided by research workers at Rice, developed a markedly different heart-assist pump. Like the earlier device, this newer model was connected between the patient's left atrium and his descending aorta. Also, both pumps were activated by pulses of pressurized air supplied from the outside. But this is where the similarity between the 1963 and 1966 models largely ends. The 1966 version had a pumping chamber that was not implanted in the patient (thereby reducing the amount of surgery required). The device's pumping action was supplied by a flexible diaphragm, rather than by a flexible tube. The pumping chamber was spherical, rather than tubular, and some of the materials of construction were different. The 1966 model's pumping chamber, which rested on the outside of the patient's chest, had an 8-cm.-diameter housing made of Lexan polycarbonate resin. Inside this housing was a flexible diaphragm made of Silastic. When a pulse of air entered the pump's smaller chamber, the air expanded the diaphragm. This, in turn, forced the blood out of the pump's larger chamber and into the descending aorta. In the next phase of the cycle, air was forced out of the pump's smaller chamber, causing the diaphragm to contract. Simultaneously, this forced the blood from the left atrium into the assist device.
The pump's surfaces in contact with blood were covered with Dacron velour. This velour reduced blood clotting and other blood damage. The 1966 DeBakey pump, like the 1963 model, forced blood into the descending aorta during the phase of the heart cycle when the heart itself was not pumping blood into the aorta. Thus, by use of the assist device, blood was forced through the body at the twice-normal rate of about 140 pulses a minute (about 70 pulses a minute produced by the heart and, between these pulses, about 70 a minute produced by the device). Operation on Mr. DeRudder. The first patient to be treated with the revised DeBakey pump, which had been used in calves for as long as 21 days, was Marcel L. DeRudder, a 65-year-old former miner from Westville, 111. For years, Mr. DeRudder had suffered from rheumatic heart disease, which had severely damaged his mitral valve, which connected his left atrium to his left ventricle. When Dr. DeBakey replaced the defective valve with an artificial valve, the patient appeared incapable of surviving without a heart-assist pump. In a six-hour operation at Houston's Methodist Hospital, Dr. DeBakey implanted his new device on April 21, 1966. The pump promptly took over 30 to 40% of the work load of the patient's left ventricle. Although the unit worked well and the patient seemed to be making progress, he died four and a half days after the device was installed.
At Children's Hospital Medical Center in Boston, James Can checks the heart and lungs of a calf in which a heart-assist device was implanted three months before 70 C&EN APRIL 12, 1971
Of the seven patients who were treated by Dr. DeBakey between 1966 and 1968 with his revised heart-assist device (in all cases, to help them recover from the open-heart surgery required to implant one or two artificial heart valves), only one patient still lives. She was operated on initially on Aug. 8, 1966, for the replacement of a heart valve severely damaged by rheumatic fever. When Dr. DeBakey concluded that his patient, Esperanza del Valle Vâsquez, a 37-yearold beautician from Mexico City, might not survive the heart-valve surgery, he implanted in her one of his new heartassist devices. This pump was used effectively for 10 days and then removed. Mrs. Vâsquez was able to leave the hospital and return home only 19 days later. Kantrowitz assist device. The Kantrowitz heart-assist device was developed primarily by Dr. Adrian Kantrowitz, Dr. Tetsuzo Akutsu, and coworkers, then at Maimonides Medical Center in Brooklyn. Because this development was assisted by Dr. Kantrowitz's brother Arthur, who is associated with Avco Corp., the pump is also known as the Kantrowitz-Avco assist device. In the Kantrowitz system, the Ushaped device is surgically implanted in the aorta at its arch. At a point between the ends of the implanted device, the aorta is then cut and sealed off. As a result, all of the blood entering the aorta must pass through the device. Thus, the Kantrowitz unit is an in-series device, whereas the DeBakey unit, through which only some of the blood entering the aorta must pass, is an in-parallel device. The Kantrowitz p u m p (not including its power supply) is fully implanted in the patient. The p u m p consists partly of a rigid outer tube made of epoxy resin reinforced with glass fibers. Inside the unit is a flexible tube made of Silastic reinforced with Dacron mesh. The blood flows through the inner tube, while pulses of pressurized air from an external source are fed into the outer tube. When the air is forced into the outer tube, it reduces the diameter of the inner tube. This, in turn, pumps the blood out of the device and into the descending aorta. Then, when the air pressure in the outer chamber is decreased, the inner tube expands as the pump fills with blood forced into it by the left ventricle. As in the DeBakey system, the device's action is carefully controlled to provide a pumping pulse when the heart itself is not pumping. Dr. Kantrowitz first implanted his device clinically at Maimonides Medical Center on Feb. 4, 1966. The patient, a 33-year-old man, survived only
Heart-assist devices Drawings show how some heart-assist pumps are connected between the heart's left side and the aorta or between one part of the aorta and another
Aorta
Left atrium
Left ventricle
DeBakey assist device (an in-parallel unit) connected between the left atrium and the descending aorta. The Akutsu assist device is connected similarly
21 hours. In the second patient, a 63year-old woman, the assist device was installed on May 18, 1966. The implanted pump did about 50% of the normal work of the patient's left ventricle. After being kept alive by this device for 13 days, the patient died. Back to laboratory. Despite the great flurry of excitement aroused by the early clinical use of the Kantrowitz and DeBakey heart-assist devices, it should be pointed out that the Kantrowitz unit has not been used in humans since 1966 and the revised DeBakey unit has not been used since 1968. Most certainly, the reason has not been a lack of potential patients. The obvious explanation is that Dr. Kantrowitz and Dr. DeBakey realized that their equipment needed to be significantly improved. Their devices caused too much blood clotting, too much damage to blood cells and blood proteins, and other serious problems. These difficulties were caused by unsatisfactory materials of construction, inadequate valves in the case of the DeBakey p u m p (the clinically used Kantrowitz pump had no valves), and other design factors.
