June 2004
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Assisting the heart: A long and winding road
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Michael E. DeBakey, MD |
The task of building a pump to aid the heart in pumping blood through the body has been a long one, fraught with barriers, shifting designs and differing endpoints.
At one point, the left ventricular assist device or LVAD, as it was called at the time, was seen as no more than a “bridge” that kept the dying patient alive until a donated heart could be found for transplant. Then for a select few patients, the LVAD became a bridge to recovery, taking over the heart’s duties until the organ rested and recovered. Keeping the metaphor alive, today’s ventricular assist systems are more than bridges. They could become a destination in themselves.
Pulsatile workhorses
Today, the ventricular assist devices or VAD, considered the workhorses that keep patients with heart failure alive, are actually based on designs that are at least 20 years old. They mimic the pulse of the actual heart and are too large to fit in the chests of many small adults and most children.
In the wings are smaller, axial flow devices that have few moving parts, no valves and can be used to aid the flow of blood throughout the body. Chief among these are the MicroMed DeBakey VAD, the Jarvik 2000, and the HeartMate II. They are still being tested around the world, and their final design is still in flux.
The final pump has probably not yet been designed, but the will to do so lies in the physiology of the failing heart. With too few hearts being donated to take care of the need and the numbers of patients with heart failure growing daily around the world, an artificial pump that will keep people alive indefinitely is fast becoming a necessity.
A recent symposium at the Texas Heart Institute in Houston called “The Implantable Left Ventricular Assist Device: From Concept To Clinical Reality” spotlighted the VAD. It is often overshadowed by the aura of the total artificial heart.
However, total artificial hearts are still far from useful clinically, but at least two left ventricular assist devices are approved for use in humans by the U.S. Food and Drug Administration. Many more of varying designs are already in human tests.
Long road to success
John Watson, PhD, oversaw the development of the heart problem from the platform of the National Heart, Lung and Blood Institute during its most formative years. From that vantage point, he told those who attended the symposium, “We are just at the beginning of the development of the implantable LVAD.”
Yet the first successful use of one occurred in Houston in 1966, when Michael E. DeBakey, MD, now chancellor emeritus at Baylor College of Medicine, implanted one in the chest of a young woman undergoing valve repair surgery. As he described it, the inflow tube was attached to the left atrium and the outflow to the right axillary artery.
“It was a simple way of getting to the aorta (the major blood vessel in the body),” he said. “It was a two-chambered pulsatile pump with two valves to maintain unidirectional flow.”
DeBakey and his colleagues had anticipated that it would be difficult to get the woman’s own heart to start working after the surgery and had the assist device waiting.
“It was truly an experimental procedure,” he said. “I was anxious to get her off the pump as soon as possible because I didn’t know what would happen.”
Even though he tried to wean her off periodically, it was 10 days before she could come off the pump safely. Eventually, she returned to work as a hairdresser in her native Mexico and left a normal life until she died in an auto crash six years later.
Development of the LVAD would have been impossible without the support of powerful national leaders who pushed Congress to support the idea, said Watson. Mary Lasker, a prominent supporter of health programs; Nobel Prize Winner Joshua Lederberg, PhD, and DeBakey were all key to getting Congress to allocate funds for development of the heart pumps, said Watson.
“In 1963, there was congressional language about forming the program, but in 1964, after Dr. DeBakey testified at the hearings, an important step was taken – the formation with congressional dollars of six studies that were competitively produced through the scientific and industrial communities defining how to develop the artificial heart.”
Eventually, the program was split in two, he said. One was aimed at developing an artificial heart and the other at caring for patients with acute myocardial infarctions or heart attacks. This led to the cardiac intensive care units that mark a hospital where the best in such care is received.
In the heart portion of the program, the goals were simple, said Watson. They were to demonstrate feasibility and insure the quality and reliability of the systems.
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REMATCH study
From the laboratory to the animal laboratory and the first trials in humans, the pace has been slow but deliberate, he said. By the time the REMATCH study began, “we had demonstrated the feasibility of these systems for clinical use,” he said.
REMATCH or Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure involved 22 heart centers around the country. The trial was designed to test the LVADs' ability to save lives and to extend those lives meaningfully.
The results from the patients who received the LVADs were tested against those in patients who received the best medical treatment available but not the device. None of the patients in the study were candidates to receive a heart transplant when it started.
The LVAD reduced the death rate by 48 percent over two years in the patients who received the LVAD compared to patients who received medical treatment only. At one year, the survival rate in LVAD patients was double that of the comparison group that received only medicine.
Yet patients continued to die on both LVAD and on medical therapy. The problem is not solved.
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“It is hard to argue that we have more than a mediocre solution to a disastrous medical problem,” said Eric Rose, MD, of the Columbia University College of Physicians and Surgeons. Rose was the lead investigator in the study.
REMATCH used the Thoratec HeartMate device, which is one of the large, pulsatile pumps with valves and several moving parts. Rose looks forward to the day when the smaller axial flow pumps with fewer moving parts come to the fore.
“There are more than 30 pumps being developed that are small rotary pumps,” he said. “Eighteen are centrifugal, 10 are axial and 2 are hybrids” of the two.
The major problem with these pumps is the need to thin the blood of patients who receive them. Yet the best known anticoagulants are 100 and 50 years old, he said. Before these pumps can go into wide use, better anticoagulants must be developed, he said.
Patient heroes
Dr. O.H. Frazier, director of the Cardiovascular Research Laboratories at the Texas Heart Institute in Houston, pioneered use of the LVADs, and he remembers patients and pumps with special affection.
“What did we learn?” he said. “The first five patients (in the bridge to transplant group) all died.”
From them he learned that when the patient’s liver and other organs fail along with his or heart, it is too late for the pump to be effective. After that, the first sign of liver failure prompted him to implant the pump. A series of 11 successful pump implantations followed. Eight of those patients are still alive.
One recent patient on an LVAD has returned to work as a barber. Another made $100,000 in investments while on the pump awaiting a transplant.
“The pumps do last,” he said. “There are 14 patients who have supported as a bridge to transplant for longer than three years.”
Cost is prohibitive, he said. However, he said, as the technology improves and more pumps are produced, the costs will come down.
“The appeal of the DeBakey and Jarvik pump is that with wider use, this simpler technology will be less expensive than the earlier pumps.”
Many of the barriers involved in the development of such pumps have been solved by close work between the physician who cares for the patients and the researcher.
“It is the obligation of the clinician to guide the research scientist to make this work productive and to translate it into the care of the patient,” he said.
He feels an obligation to the patients who placed their lives in his hands, he said.
“We all live with ghosts in this field,” he said. “It made me be more productive because I recognize the courage of our patients. Whatever the problems and barriers we face, they will only be solved by good sound science and courage and the determination of the investigator – and also the patient.”
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