by Amy Scholten, MPH
Artificial hearts have been used in patients suffering from heart failure, first as a bridge to transplantation, and more recently as a permanent implant. Known as total artificial hearts (TAH), they are not the same as ventricular assist devices (VADs), which are more commonly used to assist patients with heart failure . VADs assist the heart, whereas TAHs replace the entire heart.
TAHs have had a long, but not always successful, history. The first TAH, the Liotta, was implanted in 47-year-old Haskell Karp in Houston, Texas in 1969 as a bridge to transplantation. Haskell Karp lived with the artificial heart for about 65 hours but died shortly after receiving a donor heart transplant.
Then in 1982, a TAH known as the Jarvik-7, intended to be a permanent implant rather than a bridge to transplantation, was first implanted in 61-year-old Barney Clark. He lived for 112 days with the artificial heart, but suffered from complications, seizures , and pneumonia before dying of multiple organ failure.
As of 2005 there were at least ten different VAD or TAH devices available for clinical or research use in persons with severe heart failure. In recent years, a new artificial heart called the AbioCor was approved by the US Food and Drug Administratin (FDA) for permanent implant.
According to the Food and Drug Administration, recipients of TAHs must fit the following profile: Have end-stage heart failureHave a life expectancy of less than 30 days Be unable to receive a natural heart transplant Have no other treatment options Because only very sick patients receive these hearts, mortality remains quite high, and based on reports in the published medical literature few patients with artificial hearts have actually left the hospital. With more experience and better case-selection, the life-saving effectiveness of this technology may improve. How the Human Heart Works The human heart is divided into four chambersthe right atrium (upper right chamber), right ventricle (lower right chamber), left atrium (upper left chamber) and left ventricle (lower left chamber). The chambers work together to pump blood. The average human heart pumps blood at a rate of 60-100 beats per minute. To pump the blood, the heart contracts in two stages: Stage One: The right and left atria contract simultaneously, pumping blood into the right and left ventricles. Stage Two: The ventricles contract simultaneously to pump blood out of the heart to the lungs (from the right ventricle) and the rest of the body (from the left ventricle).
Then the heart relaxes, during which time it fills up with blood again and prepares for the next contraction. The Total Artificial Heart: A Hydraulic Pumping System The AbioCor TAH is a grapefruit-sized device with two ventricle chambers, valves, a hydraulic pumping system, and an electronics system. It is made of titanium and plastic and weighs about two pounds. It is designed to fit completely inside the body, without wires or tubes poking through the skin. The AbioCor TAH moves the blood in a rhythm, just like the human heart, and creates a pulse. Components of the TAH System The AbioCor TAH is made up of the following components: Internal Hydraulic Pump Similar to hydraulic pumps used in heavy equipment, this component moves hydraulic fluid from side-to-side of the artificial heart. A rapidly spinning gear inside the pump creates pressure to move the fluid. Porting Valve This valve opens and closes, allowing the hydraulic fluid to move from one side of the artificial heart to the other. When fluid moves to the right side of the artificial heart, blood is pumped to the lungs through an artificial ventricle. When fluid moves to the left side of the artificial heart, blood is pumped to the rest of the body.
Wireless Energy Transfer System An internal and external coil transmit power from an external battery, without piercing the surface of the skin. The internal coil picks up the power and sends it to an internal battery and controller unit. Internal Rechargeable Battery This battery is implanted in the abdomen. It allows people to take part in 30-40 minutes of activity, like swimming and showering, while disconnected from the external battery pack. Controller Unit This small, electronic unit is implanted in the abdomen. It monitors and controls the speed at which the heart pumps. Artificial Hearts May Ease Burden on Donor Supply According to the Society of Cardiovascular Anesthesiologists, more than 700,000 people die from heart failure each year. Half of these people cannot benefit from cardiac assist or replacement devices, including transplantation or TAHs. For the other half, transplantation is an option. However, only a small percentage of people can receive donor hearts each year due to a shortage in supply of donor hearts. TAHs may provide an option to fill the gap in the supply of donor hearts. RESOURCES: AbioMed (makers of AbioCor)
http://www.abiomed.com American Society for Artificial Internal Organs http://www.asaio.com References: AbioCor: implantable replacement heart. Texas Heart Institute website. Available at: http://www.tmc.edu . Accessed January 23, 2003. The dawn of artificial hearts? Society for Cardiovascular Anesthesiologists website. Available at: http://www.scahq.org . Accessed January 23, 2003. News break: University of Louisville physicians implant first AbioCor heart. University of Louisville website. Available at: http://newsbreak.Louisville.edu . Accessed January 23, 2003. Last reviewed July 2006 by Lawrence Frisch, MD Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
