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How to Build an Artificial Heart

“Thirty-five million times a year,” Cohn said.

“So, looking back on it, it’s amazing it lasted as long as it did,” Frazier said.

“Here’s what we know so far about the Little Dipper.”
Cartoon by Justin Sheen

Throughout the eighties and nineties, even as he helped with the HeartMate and AbioCor, Frazier argued that engineers should shift from pulsatile pump designs to ones based on the more mechanically straightforward principle of “continuous flow”—the strategy that Bivacor later adopted. Some researchers argued that the circulatory system might benefit from the pulse; there’s evidence that blood-vessel walls expand in response to a quickening beat. But Frazier had come to believe that, whatever the benefits of pulsation, they were outweighed by the virtues of durability and simplicity. He began working on two continuous-flow designs in parallel—one with a cardiologist named Richard Wampler, the other with Robert Jarvik—implanting them in animals, taking them out, disassembling them, and analyzing how they’d performed. By the two-thousands, the designs had come into use as the Jarvik 2000 and HeartMate II, respectively.

On his laptop, Cohn pulled up a diagram of the HeartMate II. Essentially, it’s a narrow pipe filled by a corkscrew; as the screw turns between two bearings, it acts like a stationary propeller, pushing blood continuously out from the heart and into the aorta above it. (In farming, the same design—a so-called Archimedes’ screw—is used to pump water for irrigation.)

Cohn pointed to the screw: “One moving part, suspended by ruby bearings. People said, ‘Well, you can’t have bearings in the blood.’ It turns out you can! There’s enough blood washing over them that they stay cool and clean. One of these on a bench will pump forever.” Clots are still a problem, as is infection. Still, more than a thousand people each year now receive HeartMate IIs or similar devices, living with them as they inch their way up the transplant list; a HeartMate II kept Dick Cheney alive, with a fainter pulse, from 2010 to 2012, until he could receive a transplant.

In the summer of 2019, I got an e-mail from Jess. “I recently celebrated twenty years with my heart transplant,” she wrote to a group of us. “But heart transplants don’t last as long as native hearts.” I hadn’t known this; I’d assumed that her transplant was permanent. In fact, her borrowed heart was giving out. She’d been short of breath and, one night, had almost collapsed while walking home to her apartment. Now she was back in the hospital, waiting for a second heart. “It could be weeks, or months, or (less likely) tomorrow,” she wrote. “Please send good vibes.”

I visited Jess in the critical-care unit, where we talked about restaurants, careers, and television shows. We looked at a few photos of my son, who was around a year old. I was about to visit again when she died.

“She did great,” Cohn said. “Many heart-transplant recipients are dead in ten years.”

“Recently, I went to a birthday party for a guy I transplanted thirty years ago,” Frazier said. “But those are rare, rare, rare. Only about five per cent of transplant recipients make it to thirty years.” The artificial pumps on the market are considered bridge therapies, and heart transplants “destination” therapies; but, if you live long enough, the transplants, too, are merely bridges.

I asked Frazier and Cohn how they felt about all the people who had died while, or after, using their devices—whether they lingered in the mind, and how.

“Martyrs,” Cohn said. “They were clinging to life. The technology may not have been there, but it sure beat drawing their last breath. Many of them spent years with their loved ones, doing the stuff they enjoyed. Some went to the I.C.U., were gravely ill for six weeks, and then died, when in retrospect they would’ve been better off if we’d just let ’em die. But you don’t know! It’s a statistics game, and they were willing to go for it, for a couple more days of life. And it advanced the field, every time.”

“I had a lot of experience working with leukemic children when I was a medical student,” Frazier said, quietly. “They all died. In fact, the doctors at Texas Children’s wanted to stop the work.”

“Because you were torturing them with these poisons,” Cohn said.

“They looked awful,” Frazier said. “Their bellies swelled, and they lost their hair, and it scared the other children. But they kept plugging away with it. And I think that helped me. Because the first twenty-two people of the seventy that we put the first LVADs into all died.”

It was getting late. Frazier led me through the deserted office area, along a series of twisty, silent corridors, and finally down an elevator to the basement. We entered his lab—the vast lair where he’d spent most of his working life. We passed through a veterinary operating theatre and a pathology lab, where deceased animals and failed pumps could be disassembled and analyzed.

“We’ve got pigs in here,” Frazier said, opening a door. There was an animal smell, and a large pink pig lumbered into view, snuffling.

“Pigs have a heart that’s most like the human heart,” he said, closing the door. He gestured down the corridor: “Goats. I don’t like to do goats. They’re too smart!” He laughed. “They look up at you.”

We went deeper into the lab. In a carpeted conference room, a display case contained a few dozen artificial hearts and heart pumps—the history of the field, more or less. “The one in the middle is the AbioCor,” Frazier said, indicating a heart-shaped twist of metal and plastic. “This is the old Jarvik-7”: two yellow-beige ventricles with tubes running out. “That’s a HeartMate II”: a gray metal cylinder with white tubing at either end, like something you’d find under a sink. Framed on a wall, an issue of Life, from September, 1981, declared, “The Artificial Heart Is Here.”

Frazier pointed to a big metal pump, and to a white bit of tubing protruding from it—a “long inlet,” he said. Until it was corrected, it had doomed the device to failure. Small differences, iteratively tweaked, their effects uncovered only after death. It was invention in slow motion.

The AbioCor was cancelled. The Bivacor is years away. Today, the only company manufacturing and selling artificial hearts that are actually implanted in people is SynCardia Systems, of Tucson, Arizona. The company was formed as a rescue mission. Symbion, the Utah company that Robert Jarvik helped found, had lost F.D.A. approval for the Jarvik-7 heart in 1990, because of quality-control issues; its heart technology was acquired by another firm, which ran a decade-long clinical trial with an improved version of the heart, only to exhaust its funding in 2001. For a time, it seemed that the technology would vanish from the earth. But two heart surgeons and a biomedical engineer scraped together the venture capital to buy the rights to the system; they rebranded the heart as the SynCardia Total Artificial Heart, or T.A.H. The company, now based in a handful of buildings surrounding a sandy parking lot, sells somewhere north of a hundred hearts a year, all descended from the old-style, air-powered Jarvik-7. Although SynCardia has succeeded in building a network of surgeons capable of installing its heart, the company is only tenuously in business. A few years ago, it declared Chapter 11, and was bought by new investors. It coped with the coronavirus pandemic, which has led to the cancellation of surgeries around the country, by manufacturing hand sanitizer.

With Karen Stamm, SynCardia’s director of program management, and Matt Schuster, an engineer, I watched through a window as a technician in a clean room assembled one of the hearts. “The key to being able to build the artificial heart is the material we use,” Schuster said. “Segmented polyurethane solution. You’ll hear us call it ‘spuzz’—S.P.U.S.” Stamm laughed. “We actually manufacture spus here on campus,” Schuster continued. “It’s our own proprietary mix. It comes out of our manufacturing equipment almost like a sap, or a thick honey.” Using a dental pick, the technician carefully manipulated layers of the molded honey. A translucent something shifting over another translucent something. The assembly process takes two and a half weeks.

We walked through a lab dedicated to “explant analysis”—“If we get a heart back, we’ll take it apart and inspect it,” Schuster said—and into another room filled with a few dozen water tanks on shelves. Inside each tank was a heart, beating; next to the tanks were the air pumps, or “drive units.” The sound in the room was deafening: a fast, loud whump-whump, whump-whump, and within that a mechanical clacking, like a typewriter. The sounds cycled twice a second—an industrial rhythm, as though we were in a factory for the manufacture of circulation. “This is where we run our long-term studies,” Stamm shouted, above the din. On one side of the room were the fifty-c.c. hearts, used by smaller patients; on the other, the seventy-c.c. models, used by larger ones. “There’s the driver, which is the mechanical sound,” she said, pointing to a lunchbox-like mechanical pump that was connected by an air tube to a heart inside a tank. “Then you hear the clack-clack—that’s actually the valve inside the heart.”

The drive unit has been a focus of innovation for SynCardia. Its heart can be driven by one of two units, the first the size of a mini-fridge, the second the size of a toaster—both much smaller than the ones DeVries’s patients used. The drivers need to be serviced after a few months; when a warning light comes on, a caregiver unplugs the drive line and reattaches it to another unit as swiftly as possible, lest the user’s heart skip a beat. As I watched, the water in the tanks rippled slightly, in rhythm. It takes a lot of whump to push five or six litres of blood through the body every minute.

“What does this actually sound like in a person?” I asked.

“It’s much quieter,” Stamm said. “But you can hear it. I’ve heard stories where patients say that, if they open their mouths, other people can hear the clicking.” She told me that some patients couldn’t tolerate the noise at first. But then, she said, “they couldn’t sleep without the sound of the ca-chunk, ca-chunk.”

We continued through a warehouse area, where a dozen or so hearts were kept on shelves, ready to ship; surgical kits, containing the materials required to install them, were boxed in a separate stack. Then we traversed the parking lot to another building, where a group of engineers waited with safety glasses in a high-ceilinged lab space. One of them handed me a small piece of hourglass-shaped plastic: the SPUS. See-through but slightly milky, slick but grippy on my fingertips, it was almost surreally stretchy—I pulled on its ends, drawing the neck of the hourglass to several times its initial length, and it effortlessly returned to its original shape.

Through a doorway I spied a giant, well-worn machine, perhaps a dozen feet tall, combining aspects of an oil derrick and a KitchenAid. “The SPUS reactor,” Troy Villazon, SynCardia’s production manager, said. “It’s from the early sixties.” SynCardia had acquired the machine in the early twenty-tens, to insure a steady supply. “The machinery itself has gone through the whole history of this material,” Villazon said. For a while, we stood speculating about whether this very machine had been used in the creation of the Jarvik hearts. “It very well might have,” Schuster said.

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