No Pulse: How Doctors Reinvented The Human Heart

This 10,000-rpm, no-pulse artificial heart doesn't resemble an organic heart--and might be all the better for it

By Dan Baum Posted 02.29.2012 at 12:13 pm 37 Comments

Flow State 2: Bud Frazier, pictured, has, along with Billy Cohn, installed continuous-flow artificial hearts in 50 calves, some of which have lived for up to three months. Jack Thompson

In 1995, 11 years after Saucier started NASA’s informal work on an implantable continuous-flow blood pump, some of the NASA and Baylor researchers helped create a company called MicroMed to bring the pump to market, and three years later, surgeons implanted one in a patient in Europe. (The FDA hadn’t yet approved it for use in the U.S.) By now, MicroMed had competition from a company called Thoratec, which had an Archimedes’-screw continuous-flow blood pump of its own moving through the FDA approval process. Eager to stay ahead, MicroMed made the bubble-era mistake of letting itself be acquired by a hedge fund called Absolute Capital Management, which starved the project as it imploded spectacularly, its principals facing charges of fraud. Thoratec zoomed past the wreckage of MicroMed and was soon testing its own device, the HeartMate II, in clinical trials.

The HeartMate II was an Archimedes’ screw with magnets implanted in the axle and an electric coil in the cylindrical case surrounding it—the saltshaker-shaped device that Cohn had placed in my hands. A charge zipped around the coil, drawing the screw along at 8,000 to 12,000 revolutions per minute. The axle spun on a synthetic-ruby bearing, lubricated by the blood itself. Connected to a portable battery, it let patients live fairly normal lives and was designed to stay in place forever, not merely as a “bridge to transplant.” Patients’ own hearts still worked; the continuous flow of the pump just helped things along.

And here’s where the story gets spooky. In November 2003, Frazier installed the newly approved HeartMate II to assist the failing heart of a young man from Central America who barely spoke English. His family members spoke none. So none of them fully understood Frazier’s instructions to return to the hospital frequently for follow-up. The young man walked out of the hospital and disappeared.

When he finally showed up eight months later, Frazier held a stethoscope to his chest and was stunned to hear no heartbeat at all. None. Even more-sensitive instruments would have found nothing resembling a pulse. The young man’s heart continued to flutter weakly, but it had effectively shut down. Although the HeartMate II had been designed to assist the heart, not replace it, in this case it seemed to be doing all the work: not just helping the left ventricle push oxygenated blood to the body, but pushing the blood hard enough to flow through the body, then back through the useless heart to the lungs, through the useless heart again, and into the pump to complete the loop and begin the process all over again. The reason the young man had never come back for follow-up, he told Frazier, was that he’d felt perfectly fine.

Thoratec won FDA approval of the HeartMate II in 2008, and surgeons have now installed continuous-flow LVADs alongside the hearts of some 11,000 people worldwide (among them former vice president Dick Cheney). But cases like that of the Central American man remain extremely rare. Newspapers reported that Cheney had no pulse, but in fact he and most other recipients continue to experience, as Cohn describes it, “cyclic fluctuations of pressure with each heartbeat.” Even though such fluctuations might be detectable only by an intra-arterial monitoring line hooked to a pressure transducer, they remain present. Patients walk around with videocassette-size batteries hanging under their armpits, their hearts still beating. Frazier, who invited Billy Cohn to join him at the Texas Heart Institute in 2004, has installed many LVADs. He showed me a video of one of his patients playing basketball and another participating in a hip-hop dance contest.

One of the most surprising things about the LVAD is that it does something the medical community had thought impossible: It reverses heart failure. Until the past few years, damage to the heart was thought to be permanent. But it seems that by relieving strain, an LVAD lets some hearts damaged by, for instance, heart attacks repair wall tissue and grow healthy again. Often the LVAD can be removed. “It’s like putting a cast on a broken ankle,” Cohn says. “You take it off when it’s healed. We had no idea that could happen.”

Some hearts, though, can’t be healed. And for those who continue to worsen even with an LVAD, the only choices are the increasingly hard-to-come-by transplant, or replacement with a machine. The experience of Frazier’s Central American patient told Frazier and Cohn that it was theoretically possible to replace hearts entirely with continuous-flow pumps. But that raised the kind of questions nobody had ever before had to consider. Our bodies have evolved to have blood move through us in pulses. Was a pulse necessary for reasons we couldn’t yet imagine? One possible snag that occurred to Cohn was the lymphatic system. Unlike blood, the ducts that move lymph through the body have no motor of their own. They surround arteries and get their motion from the pulse of the blood. “It was a good theory,” Cohn laughs. “So far, though, we haven’t found any evidence that continuous flow creates problems with the lymph.”

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