Getting to the heart of the matter at last

Biotechnology: Great advances have been made in designing a fail-safe artificial heart.

Health & Fitness

May 14, 2000|By Richard A. Knox | Richard A. Knox,Boston Globe

Designing an artificial heart seems like a straightforward engineering problem. The heart, after all, is not a space shuttle. It has just one job to do: pump blood.

But the agonizing early-1980s experiences of the first few people to have their failing hearts replaced by machines showed that it was anything but straightforward.

The first artificial heart recipient, Utah dentist Barney Clark, died after 112 miserable days on a heart pump powered by a bedside box the size of a washing machine.

"If it was simple, we would have done it a long time ago," said John Watson, who heads the federal government's 36-year-old artificial heart program.

But researchers have quietly tackled the challenges over the 17 years since Clark died, and now they say they're set to try to again.

The everyday work of the human heart is extraordinarily difficult to duplicate. A healthy heart beats without fail 100,000 times a day, nearly 40 million times a year.

The heart withstands an environment more corrosive than seawater, due to the hundreds of molecule-splitting enzymes in blood. It moves a tremendous volume of blood without touching off a shower of clots than can plug an artery in the brain. It responds instantly when the body demands more blood flow to rise from a chair or climb a flight of stairs. It remodels itself in response to increased exercise. It even has its own self-contained, fail-safe power supply.

Developers of the next-generation artificial heart say they have a device that comes close enough to the real thing that most ordinary activities will be possible -- although recipients of the implant will have to be ever-mindful of the two-hour battery life in the external batteries that keep the device beating.

Watson and scientists in Massachusetts and Pennsylvania who are developing these heart substitutes expect recipients will be able to run "a slow mile," or even sprint for a bus, as well as engage in most occupations, and in sports such as golf or bowling.

Before the end of the year, according to current plans, the first of these next-generation hearts, made by Massachusetts-based Abiomed Inc., will be implanted in one or more humans. Surgeons in Boston, Louisville, Philadelphia, Houston and Los Angeles are training for the experiment. But there's no telling where the first implant will be or who will get it, because that depends on where the first suitable and willing patient pops up after federal officials have given the go-ahead.

"This is the most visible clinical experiment" in the world, said David M. Lederman, Abiomed's chief executive. "It was in the '80s, and it will be again."

The risks are worth taking, Lederman and others insist, because the number of natural hearts donated for transplants have leveled off at about 2,000 per year (widespread use of seat belts and motorcycle helmets has reduced traffic fatalities among relatively young people).

Meanwhile, the number of Americans with failing hearts is mounting steadily. Partly this is because doctors are more successful now in pulling heart attack victims back from the brink of death, but they can't always prevent associated cardiac damage that often leads to later heart failure.

Moreover, few expect animal-to-human heart transplants, such as from genetically engineered pigs, to fill the demand for natural hearts in the near future.

High expectations

The new generation of artificial hearts faces high expectations. The field will be doomed, many say, by anything resembling the death-watch experience of Barney Clark, who suffered strokes and severe depression while he was tethered to the control unit of the Jarvik-7, the first-generation artificial heart.

The next patient, an Indiana man named William Schroeder, survived 620 days on the Jarvik-7, but most in the field agree with Boston ethicist George Annas that Schroeder's psychological and physical pain proved "there are fates worse than death."

"We sort of laid low for 10 years, quite frankly, because Barney Clark and the others in the 1980s created a public perception of failure," said Abiomed's Lederman.

"We really need to ensure that we do not repeat the early history of the Jarvik-7 heart," said Boston cardiac surgeon Gregory Couper of Brigham and Women's Hospital, one of the five centers recruited for the next round of human trials.

During the last 15 years, University of Arizona researchers have tinkered with the Jarvik heart, overcoming its tendency to generate blood clots and other failings so it can be used as a "bridge" to carry patients until they can get a natural heart transplant. One hundred fifty-five patients have used it, for periods as long as 320 days.

At the same time, other researchers have developed successful temporary pumps that take over the work of one or both of the heart's ventricles, the main pumping chambers. Use of these temporary "assist devices," which require external power sources like the Jarvik-7 heart, is routine in many major medical centers throughout the world.

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