Plastics and the artificial heart

Anaheim, Calif. — BiVACOR, an artificial heart that can go on beating forever using a small spinning rotor that levitates in a magnetic field, could be implanted in a human in about 18 months, heart surgeon Dr. William E. "Billy" Cohn said.

Cohn said demand for heart transplants far outstrips the supply of hearts, so heart patients need a practical artificial heart — something that is an improvement over other artificial hearts that are designed to be a bridge to a transplanted human heart.

The rotor in the BiVACOR heart does not create any friction. The device is a continuous-flow pump. "They should last forever," he said.

"There's no mechanical wear. There's nothing to wear out. Just one moving part floating in a magnetic field," Cohn said at Antec.

Cohn recapped the history of artificial hearts and detailed the BiVACOR in a keynote speech May 9 at Antec, the Society of Plastics Engineers' conference in Anaheim. Cohn is an internationally renowned heart surgeon and medical device entrepreneur. Last fall he became the head of Johnson & Johnson's Center for Device Innovation at Texas Medical Center in Houston.

Johnson & Johnson has allowed him to continue his academic work as a professor at Baylor College of Medicine. And Cohn said Johnson & Johnson has no interest, financial or otherwise, in his work on the BiVACOR heart.

Surgeons have been frustrated in their search for a machine that does not wear out, fail or cause infections and blood clots.

"If you have seams anywhere, blood clots will form on them, little pieces of clot break off and go to the brain. It's a devastating stroke," Cohn said.

Previous artificial hearts have used air hoses ​ feeding membranes of multisegmented polyurethane. Bacteria can travel up these hoses and infect the heart, he said.

Cohn said the multisegmented PUR "is very durable. But nothing's durable enough. If it's beating 100 times a minute, that's 52 million heartbeats a year. There's no man-made device, no polymer that we have now, that can take that kind of cyclic stress."

The flexible membranes would eventually tear and fail. Even so, about 80 percent of the patients survived long enough to get a heart transplant, Cohn said, as the average time in a patient for the artificial heart was 60 days.

Cohn said durability has presented a challenge in the world of mechanical hearts and a barrier to creating a permanent artificial heart.

"So limited durability. Air hoses. And the device inside the chest is going to fail capriciously. And because of those, because it's only a temporary device, it's approved for a patient who's been listed for a heart transplant," he said.

But Cohn spelled out the challenging math of heart disease, the No. 1 cause of death in the United States.

"Over 5 million Americans have some degree of heart failure, and about 50 percent of them die within five years of diagnosis. Four hundred thousand people die of heart failure every year," he said.

And they can't all get transplants.

"From the time a heart is useable to when we need to use it, has to be like that," Cohn said, snapping his finger. "So, the hearts that we get, the donor hearts, are from very special cases, which is, they have to be both dead and healthy. Big and strong. They have to be brain-dead. That only happens about 4,000 times a year, worldwide."

Surgeons transplanted about 2,000 hearts last year, Cohn said. "Those are all the donor hearts that were still beating strong. If it stops, even for 15 minutes, we can't use it.

"So, 2,000 heart transplants in the United States. Four hundred thousand dying of heart failure. We can only transplant about one in 200. So we really need a device — something we can take off the shelf and sew into a person with a desperate need," Cohn said.

And that's been the big hurdle for making an artificial heart that can last for decades: 52 million heartbeats a year. "We don't need an artificial heart that lasts a year and half. We need something you're going to have for the rest of your life," he said.

Cohn has been thinking about mechanical hearts since his elementary school classmates were handing out Valentine's Day cards.

"This BiVACOR artificial heart is my pursuit of a passion I've had since I was about 9 or 10 years old: to develop the world's first practical artificial heart and to work with people in that area," he said.

It started with Dr. Michael DeBakey, a pioneer in doing coronary bypass operations. He recruited a young heart surgeon, Dr. Denton Cooley, to Baylor College of Medicine. DeBakey had developed a total artificial heart, with a bedside machine that drove pressurized air in and out of the heart bladders.

In 1969, while DeBakey was in Washington shoring up funding for his artificial heart — which he was testing on calves — Cooley became the first heart surgeon to implant an artificial heart in a human patient.

"It was a very interesting dynamic. Denton Cooley was very, very aggressive," said Cohn, who worked with both surgeons.

They became archrivals and didn't speak for the next 40 years, Cohn said. "They built hospitals next each other, and all through the 80s, the two of them combined did more heart surgery than was done in all of Europe. They established Houston, Texas, as the epicenter of heart surgery in the free world," he said.

Cooley sewed that heart into that gravely ill patient, who was facing imminent death. Cohn said he woke up, got off the breathing machine and stayed alive for stayed on the device for about 64 hours, but he died after his kidneys failed.

Cohn was entranced: "It was the first time anybody had demonstrated that a patient could be kept alive by a machine. And my mom cut it out of the newspaper, put it by my cereal bowl. I took it to school."

The (heart) beat went on. The Jarvic heart made headlines in the early 1980s. Remember Barney Clark? It's now called the SynCardia heart. More than 1,600 people have had this heart implanted, hooked to a power source that drives air back and forth. But Cohn said the device has inflating polyurethane membranes. The long-term wear issue, again.

A newer project, by the French company Carmat, has gotten a lot of publicity. Cohn said this device uses membranes lined with pericardium, the membrane that surrounds the heart. An electrical system drives silicon oil to push flexible membranes.

"It's a very, very big device. A complex device," he said.

Cohn said heart experts have gained important insights from the evolution of another innovation: the left ventricular assist device, or LVAD. Because of the challenges faced when developing an artificial heart, other researchers decided to leave the existing, weakened heart in place and insert a pump that helps it pump blood.

Cohn said heart device and transplant pioneer Dr. Bud Frazier, of the Texas Heart Institute, did early work on the LVAD. The simple device was a can that went in your abdomen. And it was hooked to a failing heart by a tube and then hooked to your main blood vessel by another tube.

Cohn said the device was very large and had durability issues. "It was a great device to keep the patient alive until we had a heart transplant for them," he said.

That innovation caught the attention of Dr. Richard Wampler, who was interested in an ancient device, the Archimedes screw, a screw turning within a pipe used to move water uphill. Cohn said Wampler made a device about the size of a pencil eraser, for moving blood in a human heart. In the 1980s he showed it to Frazier, who agreed to work on it. Cohn said the cable with a tiny turbine blade — spinning 27,000 times a minute — moves oxygenated blood through the circulatory system.

"Nobody had ever seen anything like that. It really was pretty crazy. But Dr. Frazier put it in cow after cow after cow, and it worked fine," Cohn said. Wampler had determined how much stress red blood cells could tolerate so they would not be damaged by the spinning.

After doing many trials, they had a gravely ill patient who came to hospital at the Texas Heart Institute in 1988. He had a heart transplant six months earlier, but his body was rejecting it. He faced certain death.

"This patient was blue. His lungs were filled with fluid. He wasn't making urine," Cohn said. "They flipped the switch and turned it on, and while they watched, in 30 seconds, he went from blue to pink. He started making gallons of urine — with the new profusion his kidneys had. His lungs dried out, he got off the breathing machine. And actually, eight days later they were able to take the device out, and he went home and he lived another 10 years."

Cohn, who worked with Frazier, said it marked the first time a rapidly spinning device was implanted into a human being. That led to the development of many other spinning heart pumps — including one implanted on former Vice President Dick Cheney.

"These pumps are smaller. They're easier to implant. They're lighter. They use less energy. But they're much more durable," Cohn said.

Frazier and Cohn were discussing the current state of the artificial heart, and Frazier came up with the idea of using the little pumps. They cut out the heart of a cow and put in two of them, one in the right atrium and in the left atrium, connecting them to the circulation system. They used basic products you can find at the home improvement store for their first such devices — a continuous flow, artificial heart.

They did it in some 70 animals. The results were exciting, he said. But one of the challenges was the heart needed a separate computer to control each of the turbines, adjusting the system when the cow stood up, ate or lay down. "So it was labor-intensive, but it looked very promising," he said. There was no pumping heartbeat.

"Nobody had ever made a pulseless animal before," Cohn said.

And the heart was small — meeting a major challenge. The researchers thought it could be worth trying in a human patient who was gravely ill and had no other options. They found one, a 52-year old man whose heart was supported by a bedside heart/lung machine. Two days after getting the heart, he woke up and got off the breathing machine.

But he ended up dying of liver failure, and five-and-a-half weeks later, after consulting with his family, they turned off the heart and he died. Cohn said: "A very, very tragic, a brave patient and a brave family."

The continuous flow pumps got publicity. Frazier and Cohn gave a TED Talk about it.

But Cohn said the most important thing that came out of it was they met Daniel Timms — who had created the BiVACOR heart at the University of Queensland in Brisbane, Australia. "His father had developed heart failure and died while [Timms] was doing his Ph.D. on trying to develop a better artificial heart," Cohn said.

He said Timms, a biomedical engineer, had developed a brilliant device. "Unfortunately, nobody else thought it was brilliant. He was out of money and he showed up in our offices in the Texas Heart Institute with all of his stuff in a backpack. He came down on his own dime and he was looking for a home," he said.

The BiVACOR inventor had a team of volunteer Ph.D. engineers who helped him, without taking any salary. "We immediately identified that if this could be distilled to practice, this would be the world's first practical artificial heart," Cohn said.

The BiVACOR's rotor spins, powered by a brushless DC motor, inside a small titanium chamber, as it floats on a magnetic field. It has impeller vanes on both sides. Three electromagnets make continuous, rapid adjustments to keep it properly levitated, Cohn said.

The spinning disc with the impellers works like a fan, continually propelling the blood forward. The floating rotor can shift along its axis of rotation, moving just three-quarters of a millimeter, but Cohn said it makes a big difference in the relative efficiencies of the heart's two pumps. As the gap gets larger on one side, the left pump becomes a lot more efficient, and vice versa — an adjustment that Cohn said happens with a natural heart every time you take a breath.

It can automatically balance the blood flow. Without a heartbeat. "This device is figuring out where that exact balance is, and it's doing it 2,000 times a second," he said.

In his Antec speech, Cohn outlined the trials that led to the rotor design. The researchers kept a 3D printer busy to make varieties of the right and left vanes. They developed a special test device that would measure every level of flow resistance, at every motor speed.

And Cohn said they are able to design in a pulse. "This is digital pump. If we want a pulse, we can make a pulse! We can spin if fast, then slow. Then fast. Then slow," he said.

BiVACOR is lightweight, energy-efficient and small enough to be implanted in a child — a major advance over other artificial hearts that can be too big even to fit into smaller adults, he said.

Asked by an audience member the time frame when BiVACOR could go into a human body, Cohn said it qualifies as humanitarian device exemption under the Food and Drug Administration. He said there are "probably 18 months" to the first patient implantation.