Heart-Assist Devices

Ventricular-assist devices

A device that helps the heart pump is much easier to make than an artificial heart and is a good option for many patients. Most people awaiting heart transplants, in fact, have heart problems limited to the left ventricle.

Since 1985, 2,000 patients have received ventricular-assist devices. Most often, they help patients with failing hearts survive until a transplant becomes available. Sometimes the device gives patients a chance to recover by allowing the heart to rest and heal. Today, there is some hope that new electric models can one day serve as long-term heart replacements.

The first heart-assist device

This is a model of the first ventricular-assist device, developed and implanted in 1966 by Michael E. DeBakey of Baylor College of Medicine. It was called a ventricular bypass because blood was routed through its spherical pump instead of through the left ventricle. The device was mounted externally and had tubes that carried blood from the left atrium to the pump, then to the aorta and throughout the body.

More recent assist devices work similarly, except they are implanted in the abdomen. A tube from the device passes through the skin to the air compressor. As with artificial hearts, the opening in the skin makes the patient prone to infection.

Inside the round pump are valves that keep blood flowing in one direction and a flexible membrane that separates blood from air. The pump alternately fills with blood, then air. Air forces the blood out and to the rest of the body via the aorta.

On October 13, 1998 the first device of this type was implanted in a woman in Hershey, Pennsylvania, who is waiting for a heart transplant. Earlier models were connected to huge external air pumps. This new model is powered by an electric motor implanted in her abdomen. Rechargeable battery packs worn at the patient's side run the motor.

Since the 1960s, several groups of researchers have worked to perfect fully implantable artificial hearts. It's no small challenge. The device has to be durable and powerful, pumping 100,000 times per day, yet it has to be small enough to fit in someone's chest. And it's hard to find the right material. Foreign substances tend to make blood clot, which can cause dangerous blockages.

"It's easy to make a pump that will work for a day, but to make one that will work for weeks and years is miraculous."
O. Howard Frazier, Texas Heart Instititute

The newest heart replacements

Compressed air powered the early artificial hearts. They had to be connected by a tube to an air compressor outside the body. The opening through the skin was prone to infection, and the patient had to stay tethered to the huge machines that powered the device in their chests.

Portable electric motors run the newest artificial hearts, which are scheduled for human trials in the year 2000. With models like this one, no wire passes through the skin. Instead, an electrical coil gets implanted just under the skin. A second coil, held against the surface of skin, transmits power to the implanted coil. A backup battery also gets implanted in case the recipient wants to temporarily remove the external coil in order to shower or swim.

The National Heart, Lung, and Blood Institute funded the development of this heart by the Texas Heart Institute and ABIOMED, Inc.

How much does it cost?

The cost of implanting this heart, including five years of medical supervision after the surgery, is estimated at $148,000. The cost of a transplant without complications is currently about $284,000, also including five years of care. Cost can influence decisions about who gets a heart replacement.

What does the future hold?

So far, artificial hearts—and transplants as well—have had a very small impact on cardiovascular disease. Only about 150 artificial hearts have been implanted in humans, all for rather short amounts of time. And even though transplants are more common, about 2,500 Americans receive transplants each year. Compare that with the more than 1 million who get treated with heart catheterization.

Heart replacements are meant for patients who risk death because their irreparably damaged hearts can no longer adequately pump blood. Until now, the most that could be expected was that an artificial heart would allow a patient to survive until a transplant became available.

Perhaps this will change. New models—with promising new designs—will soon be tested on human patients. Maybe soon you'll hear the clicking of an artificial heart in the chest of one of your neighbors.