Philadelphia, Pa-- Fifteen years after the much-publicized artificial heart implants of the early 1980s, artificial heart technology is quietly moving into widespread clinical use. Two large efforts are underway to produce a total artificial heart that is designed to replace a person's natural heart.
Penn State's College of Medicine in Hershey, Pa., working with 3M Health Care in Ann Arbor, Mich., and Abiomed in Danvers, Mass., working with the Texas Heart Institute in Houston, Texas, are both working on the long-term heart replacement devices under a National Heart Lung and Blood Institute contract program. The devices are expected to undergo additional tests in animals later this year and could be tested in humans within five years.
Temporary ventricular assist devices, which take over the function of the natural left ventricle, are being used in increasing numbers to keep alive, and even enable the rehabilitation of, patients awaiting heart transplantation. Despite the fact that available systems require wires or tubes traversing the skin, these systems have worked well enough to be considered as alternatives to heart transplantation. Penn State's long-term ventricular assist device, a completely implanted device that allows the skin to remain intact, is being developed for clinical use by Arrow International, Inc. of Reading, Pa.
But how did we get to this point and what do researchers face in the coming years? Alan Snyder, Ph.D., senior research associate at Penn State's College of Medicine, discussed this today (Feb 17) when he described the history of artificial heart research at the American Association for the Advancement of Science 150th Annual Meeting in Philadelphia. Snyder is the organizer of a five-member panel scheduled to take part in the session, "Patients, payers and protocols: Heart replacement devices entering clinical practice."
"The heart's primary function as a pump has been recognized for many years. Early demonstrations of the heart-lung machine in 1953 showed that this pumping function could be achieved mechanically without serious harm to the patient. Experiments in dogs in 1957 showed that a dog's heart could be removed and replaced, at least for minutes or hours, with a mechanical substitute," says Snyder, who has worked on the project along with the research team at Penn State for more than 20 years.
He adds, "By 1963, prominent members of the medical community were willing to testify before congress that, with proper funding, a working artificial heart could be developed in fairly short order. We would soon realize that this task was much harder than had been thought."
"In the late 1960s, it was recognized that making sure the devices would be not damage blood, would not shed blood clots, and would work reliably for two years or more would be formidable tasks. The average heart will pump more than 30 million times in a year. Trying to duplicate this is a great challenge."
Snyder also says that while the goal of a total replacement for a natural heart is still present today and was the driving force initially, the left ventricular assist device (LVAD) has saved thousands of lives and continues to be a major part of heart replacement research. The first application for the LVAD was to permit recovery of a damaged natural heart.
"Surgeons realized that many patients could benefit from a temporary mechanical circulatory support -- a pump that could maintain circulation to the organs while the heart rested and recovered. It was expected that most patients would require support of the left ventricle only, so only a single pumping chamber would be required," says Snyder.
Today LVADs are used mainly to keep patients alive until a heart transplant is available. However, the number of donated hearts has remained at about 2,000 for several years. This means that while patients can survive longer and do better with the LVAD, these patients compete for a severely limited organ supply and the number of patients who ultimately survive has not increased. Therefore, the medical community looks to long-term LVADs and total artificial hearts as solutions for a large number of patients.
It is estimated that just in the United States up to 20,000 people per year could benefit from a totally artificial heart and perhaps twice that many would benefit from LVADs.
Snyder explains that challenges still are ahead. Devices intended for long-term use, two years or more, must undergo strictly controlled durability testing before widespread clinical use is considered. The Penn State group expects this formal testing to begin later this year.
Snyder's group continues work to design smaller devices for smaller patients, increase durability to five years or more, and reduce the need for recharging of batteries.
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