CPR for the Artificial Heart
At four U.S. medical centers, surgeons, nurses and anesthesiologists are quietly scrubbing in for the return of one of the most vilified medical devices ever conceived-the artificial heart. Each of the four teams was tapped a year ago by Abiomed, a little-known Danvers, Mass., company whose engineers have worked for more than a decade to build a 900-gram electromechanical pump they call the PulsaCor. Surgeons at the Texas Heart Institute and Massachusetts General Hospital, among others, are now practicing putting the synthetic heart into calves. David Lederman, Abiomed’s CEO, says they’ll be performing the surgery on a human before 2000 is out.
That first patient will, in all likelihood, already be dead. Lederman confides that Abiomed, moving cautiously, will seek permission to undertake a surgical dry run on a brain-dead individual on total life support. Before the doctors and nurses don their gloves, Abiomed’s recently convened board of ethical advisors will have spent months overseeing the selection of candidates. What’s more, Lederman has devised a complicated credit-sharing scheme to ensure that no single player steals the limelight of what he believes will be a “very visible” event. Even the decision to grant TR access to Abiomed’s engineers and facilities was a carefully considered media “test case.”
The reason for this extraordinary kid-gloves approach is the artificial heart’s troubled history. A one-time medical miracle, the device now resides on the short list of technologies American society has labeled “Just Not Worth It.” How it ended up there, alongside supersonic planes and nuclear power plants, is a story that dates back to 1982, when a University of Utah surgical team replaced the diseased heart of 61-year-old dentist Barney Clark with a device called the Jarvik-7. Powered by air cables running from a washing-machine-sized console into Clark’s chest, the pneumatic pump proved that a mechanical heart could sustain human life. Clark lived for 112 days. The second patient to get the Jarvik-7, William Schroeder, lived for an amazing 620 days.
If you call it living. Boston University bioethicist George Annas, an expert on human experimentation, says: “I talked to Bill…and he hated the artificial heart. There are things that are worse than death and this was one of them.” By the 21st day the device had infected Schroeder’s blood. For 420 days he had a fever. For 366 days, he was fed through a tube. Four times, Schroeder suffered strokes as hardened clots of blood that had built up in the heart broke off into his bloodstream. As the Jarvik-7’s deadly failings became plain, the media’s breakthrough hype turned to condemnation of a cruel and premature experiment.
Now, the concept a New York Times editorial once termed “The Dracula of Medical Technology” is back-and some old, thorny questions are back with it. Some say the government’s artificial heart program (which paid for Abiomed’s R&D until now) is a creature of politics, not science. Others fear another precipitate adventure by gung-ho surgeons. And many question whether a machine will ever amount to anything more than a misery-prolonging understudy for heart transplantation.
In Abiomed’s suburban labs a PulsaCor pumps away in a tank of salt water, hardly stirring the plastic balls that float on the tank’s surface to stop evaporation. The salt, which mimics the body’s corrosive effects on metal, is part of extensive lab testing to determine whether this titanium-and-plastic device can pump 160 million times without failing-enough to move the 2 million liters of blood a patient needs to live for five years.
Like the human heart, the PulsaCor has four valves that gate blood’s entrance and exit. But that’s where the similarity ends. This heart has only two chambers, instead of four-transparent hamburger-bun-shaped plastic domes clamped onto either side of a metal housing. This sealed, hockey-puck-sized core contains an electric motor that powers a spinning blade through hydraulic fluid. The fluid pushes out against two diaphragms that squeeze blood out of the chambers, through the valves, and into the arteries.
Unlike the Jarvik-7, Abiomed’s PulsaCor is designed to fit entirely inside the body, so that the patient can leave the hospital, and perhaps even return to work. To achieve this goal, the system includes an implantable battery and “controller package” containing the electronics that dictate the pump’s speed. Each is about the size of a small paperback novel, wired to the pump but implanted in the abdomen. Because the lithium-ion cell can only feed the pump’s 12- to 20-watt power demand for about an hour, it will have to recharge continually from a wearable external battery pack. A pair of spiral induction coils-one outside the body, one inside-spirit electrical energy across the skin. It’s an odd arrangement but, says Robert Kung, Abiomed’s chief of engineering, “any cable going through the skin is an invitation to infection.”
Several technical advances since the days of the Jarvik-7 have brought the goal of a totally implantable artificial heart within reach. Better batteries, for example, make it possible to eliminate the external power source that kept Clark and Schroeder tethered to their hospital beds. Faster computer processors have allowed engineers to model blood’s movement through artificial chambers and valves, and thereby eliminate spots where blood might pool and clot.
Still, creating a pump that is ultra-reliable, extremely power-efficient and small enough to fit in the 12-centimeter space between the backbone and rib cage has required some engineering stretches all around. Stresses on the flexing dia-phragms are high and unabating, but kept shy of the threshold at which cracks can form. The valves are clot-resistant, but not clot-proof-patients will still need to take blood-thinning drugs. The controller package and battery will leak heat into the body, but less than the 2.3 milliwatts per square centimeter that can damage the surrounding tissue. David Myerson, an electrical engineer turned cardiologist at Johns Hopkins University, compares the artificial heart with the Stealth bomber: “Both are engineering outliers. It flies, but it takes every trick you’ve got.”
The engineers who have worked on artificial hearts have had 35 years to learn some of these tricks. The National Institutes of Health (NIH) established the Artificial Heart Program Office in 1964 at the urging of Baylor College of Medicine heart surgeon Michael DeBakey. At that time, the advent of heart transplantation was three years away and patients whose hearts failed faced certain death. Many thought a mechanical replacement would take only a decade to develop-in the age of the Apollo mission, pushing blood through a pump looked eminently doable.
“The original expectation was that you could take existing components and put it together. That turned out to be a false assumption, ” says John Watson, director of the NIH’s National Heart, Lung and Blood Institute’s (NHLBI) office of bioengineering, which now funds the artificial heart. Up close, the project was a hydra, with unexpected materials, power and design challenges sprouting everywhere.
Technology wasn’t the only problem. “The symbolic meaning of the human heart seems to carry people away, and blind those involved to what the obstacles are,” says Rene Fox, a medical anthropologist at the University of Pennsylvania. In her 1992 book Spare Parts, Fox chronicled how the combination of technological shortcomings and surgical zeal led to the Jarvik-7 fiasco.
Since the ’80s, the artificial heart has struggled to survive-and has gotten caught up in a battle between politicians and NIH leaders. In January 1988, spending legislation required NHLBI to award $22.6 million to four contractors (including Abiomed) to design and build a totally implantable artificial heart. NHLBI officials, citing inadequate technology, canceled the contracts a few months later, only to reinstate them when Sens. Ted Kennedy and Orrin Hatch (both of whom had constituents working on the project) intervened. Since then, the program has been moving ahead with little fanfare-but under suspicion that politics, rather than science, is driving it forward.
By now NHLBI has thinned the field from the original four to just two teams: Abiomed and Pennsylvania State University (whose heart is similar to Abiomed’s in conception, but different in detail). Each team has received approximately $13 million from NHLBI so far, placing them ahead of less-well-funded efforts at universities in Europe and Japan. In 1997, Lederman says, his technical staff and advisors concluded it was time to start putting Abiomed’s own money behind the project, separating it from the academic pack and moving ahead of the NHLBI schedule (at Penn State, researchers don’t expect clinical tests before 2001). In 1998, Abiomed poured $10 million into the PulsaCor project, and this year Lederman expects to spend even more.
For the time being, Abiomed doesn’t have any commercial competitors. The artificial heart’s daunting engineering challenges, combined with its troubled public image, says Victor Poirier, CEO of Waltham, Mass.-based Thermo Cardiosystems, mean that “the only reason people have continued to work on the artificial heart is because the government paid for it.” Thermo dropped its own program years ago and, along with most of the field’s other players, has turned its attention to a simpler type of implantable pump known as a left ventricular assist device (LVAD), which aids a weak heart rather than replacing it.
The Food and Drug Administration (FDA) has already approved the use of the LVAD as a temporary “bridge-to-transplant” that helps patients in need of a human heart hold out until a donor organ becomes available. Bridge-to-transplant would be an obvious initial application of a total artificial heart, but because of ongoing negotiations with the FDA, Lederman won’t say if this will be the first use of the PulsaCor. Ultimately, he says, Abiomed plans to prove the artificial heart’s mettle as a permanent implant for the 315,000 Americans that he estimates die every year from sudden heart attacks and other types of acute heart failure that leave no time for transplants. “That is the bulk of patients that we have to deal with,” says O. H. Frazier, a top scalpel at the Texas Heart Institute and longtime Abiomed collaborator. “We had a 40-year-old who came in last night with a [heart attack] and basically his heart was destroyed. The only thing that could have saved him was a total artificial heart.”
Will that 40-year-old really be a typical artificial heart recipient? Opinions differ. Mehmet Oz, a surgeon at Columbia Presbyterian Medical Center, thinks the device will find a much more limited role, primarily as a replacement when a transplant recipient rejects a donated heart and isn’t eligible for another. Others are even less optimistic. “I have some doubts about how well it will do as a permanent implant,” says DeBakey. “History tells us this is very difficult.”
Whatever their degree of skepticism, all observers agree that only human tests will yield answers. Lederman has promised tests on people will begin before the end of next year. As TR went to press, however, Abiomed engineers were still tweaking the heart’s final design; the FDA will require Abiomed to run some 12 to 20 units in the lab for up to one year with few or no mechanical failures before human studies can get under way.
And though Abiomed’s animal tests look promising, the transition from healthy calves to sick humans presents many unknowns, says Richard Smith, head of the artificial heart program at the University of Arizona. How will human skin react to the electricity-conducting coils, for example? “We are going to have to learn the way we always have learned-which is the hard way,” Smith says.
That view is widely shared, and Alan Snyder, who heads the engineering team working on Penn State’s heart, warns that the public should have realistic expectations. He notes that even patients who have had only one heart valve replaced with a mechanical substitute have some chance of stroke. With four synthetic valves, he says, “you have to realize that things will happen to these patients that we wish wouldn’t.”
At Abiomed, Lederman continues to do all he can to make history without repeating it. But no amount of technical care or ethical caution, advisory boards or media test cases can say for sure how the PulsaCor will fare in human testing. “Sooner or later,” Frazier says, “we will have to move forward with some uncertainties still.”
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