The Artificial Heart, Ventricular Assist Devices

by Food and Drug Administration (FDA)

(Page 3 of 3)

The Artificial Heart

In the 1980s, four men lived for varying amounts of time with artificial hearts. But problems were rampant. The plastic, metal and Velcro of the heart attracted bacteria to areas inaccessible to many antibiotics. The device also caused blood clots, triggering strokes.

As a result, life for the "permanent" artificial heart recipient was difficult. Recipient William Schroeder, for example, suffered from strokes, seizures, fever, and depression on many of his record-setting 620 days with the Jarvik-7 device, which was then used predominantly as a short term "bridge to transplant." But even this temporary use was halted in January 1990.

The attachment of the Jarvik device to the bulky exterior equipment is thought to be a route of infection. So many scientists hope a fully implantable, electrically driven artificial heart can be developed. Other artificial hearts are under development at the University of Arizona in Phoenix, the University of Utah in Salt Lake City, Pennsylvania State University in Hershey with 3M Corp., the Cleveland Clinic Foundation with Nimbus, Inc., Temple University in Philadelphia with Abiomed, Inc., the Minneapolis Heart Institute, and the Texas Heart Institute in Houston.

Ventricular Assist Devices

A currently more fruitful area of research is the electrically powered implantable ventricular assist device, a pump used to support the patient's left ventricle, the chamber that must work most vigorously to send blood on its way throughout the body. The 1970s and 1980s saw a variety of experimental left ventricular assists, all tethered to outside support equipment. Used as a bridge to transplant, the device is promising.

In a study reported by R. Gaykowski, L. Barker, and W. Yates at the 34th annual meeting of the American Society for Artificial Internal Organs, 92 heart patients received Jarvik-7 devices while awaiting a heart transplant. Of these 92, 63 received donor hearts, and 35 of these survived, a survival rate after transplant of 56. In a similar evaluation of patients using the ventricular assist to sustain them until a donor heart became available, survival after transplant was 82.

The difference in performance between the two devices may be anatomical location or technology complexity. "The technology for both devices is similar. But control of the total artificial heart is more difficult, because there are both left and right ventricles that must be integrated," says the National Heart, Lung, and Blood Institute's Watson.

One type of totally implantable ventricular assist device is a blood pump about the size of a softball, inserted beneath the heart in the muscles of the abdomen. Blood from the left ventricle is diverted to the pump, which then sends it to the aorta, the largest artery in the body. The pump senses when to boost the blood by way of an electrically driven control unit that monitors the cardiac cycle.

The control unit, about the size of a deck of cards, is also implanted in muscle. The implanted miniature electrical engine and rechargeable battery are charged from the outside by a coil and battery pack worn by the patient. The external coil is coupled to a second coil implanted under the skin of the abdomen.

"We expect to begin implanting the device in people for clinical study in the fall of 1991. We are now in the process of fabricating the systems, selecting clinical centers, and developing protocols that will require an IDE [investigational device exemption] from the FDA," says Watson.

Many cultures have regarded the heart as the center of a person's being. In the coming century, scientists hope to beat heart disease by a prudent combination of prevention and an arsenal of cardiovascular spare parts.

Blood's Journey Through the Heart

The human heart is built of four chambers. The upper chambers — right and left atria — receive blood from the veins. The lower chambers — right and left ventricles — pump blood into the arteries. Valves keep blood flowing in the proper direction.

Blood that has given up its oxygen to the tissues enters the heart at the right atrium. It passes through a valve to enter the right ventricle, from which it crosses a valve to enter the pulmonary artery. The blood then travels through the lungs, picking up oxygen and losing carbon dioxide. The newly oxygenated blood then flows through the pulmonary vein to the left atrium of the heart. The blood passes through another valve to enter the left ventricle, from which it exits the heart through a valve into the aorta, the largest artery. From the branches of the aorta, the blood travels in increasingly narrow arterial vessels, releasing its oxygen to the tissues along the way. The deoxygenated blood travels back to the heart in vessels that gradually increase in diameter, until the blood is in the two branches of the venae cavae, the veins that empty back into the right atrium.

About the Author

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