Artificial heart

Because the heart functions primarily as a pump to keep blood circulating through the body, medical researchers have long attempted to develop a mechanical pump to take over its job in the event of damage or disease. In 1935 the French-born surgeon Alexis Carrel, and famed American aviator Charles Lindbergh(1902-1974), designed a perfusion pump that kept excised organs, including the heart, alive by circulating blood through them. News reports called this device an "artificial" or "robot" heart. The first total artificial heart (TAH) was implanted in 1957 in a dog at the Cleveland Clinic by Willem Kolff, a Dutch-born surgeon, and Tetsuzo Akutsu. Kolff later led a medical team at theUniversity of Utah at Salt Lake City in developing the artificial heart. At the urging of another TAH pioneer, Michael DeBakey, the United States government, through the National Institutes of Health, established an Artificial Heart Program in 1964 to develop both partial and total artificial heart devices. By 1966, DeBakey had designed and implanted a pneumatically driven component called a Left Ventricular Assist Device (LVAD) to serve the chamber of the heart that pumps blood out into the arteries. This was an important development, for the great majority of severe heart disease is caused by left ventricle failure.

The first human artificial heart implant was carried out by Denton Cooley andhis surgical team at the Texas Heart Institute in 1969. The pneumatically driven Dacron-lined plastic heart, designed by Argentine-born Domingo Liotta, was a temporary measure to keep a patient alive until a heart transplant couldbe performed. Artificial heart implantation captured worldwide headlines in1982 when the first TAH intended for permanent use was implanted in the chestof a patient on the verge of death--dentist Barney Clark. The procedure wasdone at the University of Utah by a surgical team headed by William DeVries.The device, called a Jarvik-7, was designed by American physician Robert Jarvik. The plastic and titanium pump was powered by compressed airdelivered by a large external air compressor through two tubes that passed into the body via incisions in the abdomen. Clark survived for 112 days. DeVries then joined the staff at Humana Hospital in Louisville, Kentucky, where hecarried out four other Jarvik-7 implants during 1984 and 1985. Each of thesepatients also died, including William Schroeder, who suffered a repeated series of debilitating setbacks during his 620-day struggle to survive. The results of permanent implantation of the Jarvik-7 revealed its insurmountable limitations: it caused blood clots to form, which traveled to the brain and precipitated stroke; the abdominal incisions provided a pathway for infection-causing bacteria; and the patient's mobility was severely restricted by the cumbersome compressor. These problems and the concurrent development of successful heart transplantation, permanent installation of the Jarvik-7 and any otherTAHs rapidly fell out of use, especially after Schroeder's death in 1986.

At the same time as heart transplantation became an established procedure forterminal heart disease, demand for donor hearts outstripped supply. In 1998,more than 50,000 Americans could benefit from a heart transplant while the available number of donor hearts remains steady at approximately 2,000. The mechanical heart thus became a "bridge for transplantation"--a last resort to keep a patient alive until a donor heart became available. Meanwhile, researchfocuses on a new generation of electrically powered artificial hearts, bothTAHs and LVADs which use portable battery packs to transmit power via radio signals through unbroken skin to an implanted mechanical heart pump. The firstof these devices was experimentally implanted in a human subject in 1991. While no significant progress has been made, two groups of researchers are working under the National Heart Lung and Blood Institute contract program. One group--The Texas Heart Institute and ABIOMED, Inc., anticipates clinical trials of a new TAH by the year 2000. The second--Pennsylvania State University College of Medicine and 3M Health Care--foresees formal testing of a long-term(two-year) LVAD beginning in 1998. A third study at the University of Pittsburgh Artificial Heart Program aims at improving fluid dynamics in artificial hearts by minimizing reverse blood flow within the pump which causes blood clots.

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