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Hearts empowered

For more than three decades, Gerson Rosenberg, voted the 15th Design News Engineer of the Year, has pursued the goal of designing reliable devices to assist-or replace-failing hearts

by Lawrence D. Maloney, Editorial Director -- Design News, March 11, 2002

Dr. Gerson Rosenberg, the 15th annual Design News Engineer of the Year.

HERSHEY, PA — HERSHEY, PA—In 1967, just three years after President Johnson challenged the medical community to design an artificial heart, the world received a startling report: South African surgeon Christiaan Barnard had successfully transplanted a human heart.

"When we heard that news, some people thought that the artificial heart was a good idea whose time had suddenly passed," recalls Dr. William Pierce of the Milton S. Hershey Medical Center, at that time a young surgeon beginning research on heart pumps.

Thirty-five years later, heart transplants have indeed become commonplace. Moreover, most patients receiving donor hearts can now enjoy 15 or more years of extended life, thanks to better tissue matches and advances in immunosuppressant drugs.

Still, one glaring problem has not changed over the years: an acute lack of donor hearts. In the U.S., only about 2,300 donor hearts are available for transplant each year.

Contrast that number with the nearly five million people in this country who suffer from congestive heart failure—the inability of the heart to adequately pump blood. Some 550,000 new cases are reported each year, with annual medical costs approaching $40 billion. Thousands die each year waiting for donor hearts to become available. Tens of thousands more don't even qualify for donor hearts, because of advanced age or such accompanying diseases as diabetes, kidney failure, cancer history, or pulmonary hypertension. As their condition worsens, these patients live a bedridden existence, fighting for breath, as muscle tissues and vital organs gradually fail. Despite advancements in medications, half of those diagnosed with heart failure die within five years.

Penn State's pneumatically driven heart-assist pump is considered an International Historic Mechanical Engineering Landmark. The device, first used clinically in 1976, was not implanted but instead rested on the patient's abdomen. As shown in this drawing, air pushing against the diaphragm compresses a plastic sac, propelling the blood through an outlet valve.

A long journey. But just as heart transplants have not solved the widespread—and growing—problem of heart failure in an aging population, designing devices to assist or replace ailing hearts has been equally elusive. Worldwide, less than 5,000 patients have received heart-pump implants, estimates Dr. Pierce (who in 1970 came to Penn State's new medical school in Hershey, PA, to start what has become one of the nation's leading artificial heart research programs). Moreover, most of these patients have relied on the devices for only a few weeks or a few months—either to allow their hearts to recover following major cardiac surgery, or to keep them alive while awaiting a transplant.

"When I first started in this field, estimates when these devices would become available were incredibly optimistic,'' remembers Gerson Rosenberg, a Ph.D. mechanical engineer who joined Pierce's research team as a graduate student in 1970 and now heads the Division of Artificial Organs at Penn State's College of Medicine in Hershey. "People were saying that we would have left ventricular assist devices (LVADs) or even a total heart artificial heart in five years."

Rosenberg, who has put his engineering stamp on several important heart-assist designs that have come out of the sprawling medical complex in this candy capital, was not one of those Pollyannas. It would be a very long haul, he realized, as he conducted animal research at Hershey in 1973 with early pump designs and tackled such key issues as blood flow and oxygen consumption in the heart muscles.

"At that point, I realized what a difficult problem it would be," says Rosenberg. "I be-came aware of all the problems you encounter with these blood pumps: clotting, destruction of red cells, biocompatibility issues, the durability of components, and control systems. There was just so much work to be done."

Fortunately, Rosenberg and his 20-member core team of engineers, surgeons, and technicians have stayed the course. Out of some 30 teams that once pursued the dream of designing artificial hearts after the National Heart, Lung and Blood Institute began funding the research in 1964, Rosenberg's group is one of a small handful who remain. And the long years of effort were rewarded in 2001 with several milestones that could lead to widespread use of heart pumps not just for temporary therapy or "bridge to transplant" but as a long-term alternative for tens of thousands of people suffering from heart failure. Among these developments:

• In February 2001, clinical trials began in the U.S. to implant an electric-driven LVAD, originally designed by the Rosenberg team and manufactured by their commercial partner, Arrow International (Reading, PA). Called the LionHeart™, it is the first LVAD powered by wireless electric transmission. Since no wires or tubes protrude through the skin, the system reduces chances for serious infections.

• Abiomed, Danvers, MA, captured worldwide attention when its total artificial heart, driven by an electro-hydraulic system, was implanted in five heart patients who had been expected to die within a month. The very first recipient lived for nearly six months, and the Food and Drug Administration (FDA) granted approval for 10 more implants. Time magazine called the AbioCor "the invention of the year." And there's more: Abiomed, which has acquired exclusive rights to commercialize the Penn State team's electromechanical total artificial heart, is targeting 2004 for clinical trials for that device.

• In its November 15 issue, the New England Journal of Medicine published the results of a three-year landmark study (see sidebar) comparing the survival rates of heart-failure patients who had received LVADs versus those who remained on traditional drug therapies. The key finding: Those who received LVADs lived twice as long as those on medication and enjoyed a higher quality of life. Experts believe the results are a very significant step in convincing cardiologists that heart assist devices can be an effective, long-term therapy for such patients.

These events have boosted the spirits and resolve of Pierce, Rosenberg and others who have spent their careers developing heart-pump technology. More importantly, the technologies that they have spawned now seem to be on the verge of widespread clinical use.

"We are very optimistic about the opportunities that the LionHeart LVAD promises," says Phil Fleck, president of Arrow. "Worldwide, about 100,000 people die each year from end-stage congestive heart failure—40,000 in the U.S. alone. Even if we could help a small portion of them with our device, the opportunities for our company could be very significant."

In 2001, surgeons implanted Abiomed's electro-hydraulic total artificial heart in five terminally ill patients. The company is now collaborating with Rosenberg's team on an electromechanical total artificial heart targeted for women and smaller male patients.

Building the team. Having a device that they designed on the verge of commercialization was a distant dream for the interdisciplinary team that Dr. Pierce formed at Hershey in the early '70s. Earning a chemical engineering degree from Lehigh University before entering medical school, he realized very early that designing heart-assist devices would require the skills of a broad-based group, including: surgeons, physiologists, mechanical engineers, control engineers, machinists, fabricators, and animal husbandry specialists.

One of Pierce's earliest disciples was a 25-year-old graduate student in mechanical engineering named Gerson "Gus" Rosenberg. From the town of Chalfonte 30 miles northwest of Philadelphia, Rosenberg, who loved to tinker with cars, was learning to be a machinist when a college friend got him excited about engineering. Later, in his senior year as a mechanical engineering student at Penn State, Professor John Brighton recruited him to join Pierce's fledgling research team.

Recalls Brighton: "Gus very quickly saw the potential benefits of the research. He was very bright, steady, and ready to take on a challenge. His courage to step into a situation and get things done was very impressive."

One of the first things that Rosenberg "got done" for the research team on his way to getting his Ph.D. was to design a mock circulatory system for evaluating the performance of a left ventricular assist device. The system, which the National Institutes of Health adopted in 1975 as the standard mock loop for research, consisted of four spring-loaded, rolling diaphragm-type piston cylinders, which simulated the resistance and compliance functions of the veins and arteries. Two nonlinear artificial atria could be added, and systemic and pulmonary resistance could be simulated by compressing flexible tubes between flat plates.

Among its many applications, Rosenberg's mock circulatory system has aided the design and calibration of control systems for heart-assist devices, as well as determining the optimal placement of cannulae connecting the pump to the heart.

In those early years, Rosenberg worked closely with Dr. Pierce and fabricator Jim Donachy to design and build the Hershey team's first pneumatically-driven heart pump, used on patients beginning in 1976. Besides pioneering fluid mechanics in blood pumps, the design debuted the use of segmented polyurethane as a blood-contacting material. It also featured an extremely smooth, seam-free surface in the internal blood sac to prevent clotting that can lead to deadly strokes.

Recognized as an International Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers, that first pump was not implanted but instead rested on the patient's abdomen. It consisted of a rigid plastic outer housing that contained an assembly featuring the plastic blood sac. Compressed air entering the pump from a refrigerator-size drive unit pushed on a diaphragm surrounding the blood sac, causing the blood to be propelled through a tube passing under the patient's skin and connecting to the ascending aorta. Another tube, attached to the left atrium, returned blood to the pump for the next cycle.

Typical of the first patients helped by the new device was a 35-year-old woman who was having difficulty coming off the heart-lung machine after heart-valve surgery. After a few days on the pump, her own heart had recovered enough to function without any assistance.

"All of us were at her side monitoring the drive unit—Dr. Pierce, Gus, myself, and others on the team," recalls Allen Prophet, who operates the animal research facility for the artificial heart program. "After being at death's door, she survived. That event showed us all that this technology was not just a laboratory curiosity but held real promise for helping people."

That initial pneumatic design, approved by the FDA in 1980 and manufactured by Thoratec, has helped more than a thousand patients over the years as a bridge to transplant or as a temporary assist following open-heart surgery. With modification, two such pumps working together also have served as a total artificial heart for patients awaiting transplants, keeping individuals alive for several months.

The next big thing. Despite those early successes, Rosenberg and his colleagues understood that widespread use of the technology demanded the development of a compact, fully-implanted device that would allow patients freedom of movement, including work and exercise. "By 1978, we realized that a wireless, electromechanical system was the way to go," notes Dr. Pierce. "That has been Gus' baby, and he has been an excellent team leader."

Designing a wireless device that could last a minimum of two years, and ideally five years or more, required advances in every part of the system. By one estimate, the job demanded some 800 different design steps. Among the major concerns:

• A reliable miniature brushless dc motor had to be developed and customized to drive the implanted pump.

• Advances had to be made in materials and coatings for wear parts, such as bearings and the roller screw that actuates a pusher plate to compress the blood sac.

• Inductive coupling devices, featuring both implanted and external components, had to be designed to deliver power to the implant.

• Implanted electronics, including a rechargeable nickel-cadmium battery, had to be downsized to fit in a thin-walled, hermetically-sealed titanium package.

• External electronics, such as the power transmitter and battery charger, had to be designed from scratch.

• Much care had to be taken in the design of pump connectors and cannulae to avoid problems with erosion and bleeding.

All this, plus the most daunting task of all: finding and then fabricating the precise polyurethane material into a blood sac durable enough to withstand 100 million pump cycles in the course of a two-year life.

Through it all, say colleagues and industry experts alike, Gus Rosenberg was the glue that kept the Hershey research team together. And his style, like Dr. Pierce's, was quiet, calm and unassuming—focusing on incremental progress, not big breakthroughs.

"This work is so hard and it takes so long that you need leaders who have a steady vision of where they want to go and can help the team weather the inevitable ups and downs," says electrical engineer Bill Weiss, who spearheaded design of the transcutaneous energy transmission system. "Gus Rosenberg and Bill Pierce have done a tremendous job providing that leadership."

Designer and inventor. Observes Win Phillips, a former team member who is now vice president of Research at the University of Florida: "Gus Rosenberg is one of the most creative systems engineers I have ever known. His expertise certainly is in electromechanical design, but he has a thorough knowledge of every component that goes into those heart-assist devices. As the chief engineer of the Hershey projects, he was hands-on enough to make a part from scratch if he needed to—or find a vendor who could do it. In the forefront of a brand new technology, he had to be both a designer—and an inventor."

Rosenberg also had to be a fund-raiser and a tireless advocate for heart-assist technology. The Hershey program has received nearly $50 million in grants over the years—about three quarters from NIH—but money has been a constant worry. "We've been applying for grants from day one," says Rosenberg.

For a time, in 1988, the entire program seemed doomed, when NIH suspended funding for the artificial heart program. The reasoning was that the money would better be spent on developing ventricular-assist devices. But with support from Penn State, and closer cooperation between the Hershey group and three other teams working on the technology, research continued.

NIH subsequently restored the funding, but it asked the Institute of Medicine (IOM), an arm of the National Academy of Sciences, to evaluate the artificial heart program. As evidence to the respect that Rosenberg had achieved in the field, IOM chose him to write a key research paper on the potential of heart pumps and artificial hearts.

"Rosenberg's paper was extremely important," observes Dr. John Watson, who has evaluated heart-assist technology for many years at the National Institutes of Health. "If he had not been able to demonstrate that the technical challenges could be solved, this research would have stopped."

But with additional NIH funding and the help of a corporate partner, 3M Cardiovascular Systems, the Hershey team's work continued. In 1991, a calf named Holly survived for a record 13 months on an electric total artificial heart that used skin-piercing wires attached to an external controller. The very next year, the team also had success with animal implants of the world's first total artificial heart featuring a wireless or transcutaneous system (see sidebar on components and systems). In those early years, recalls animal lab director Prophet, "Gus and the other engineers often spent entire nights monitoring the equipment to keep the animals alive."

Going to market. Rosenberg realized, however, that it would take a lot more resources than Penn State had to get the heart-assist devices out of the lab and into clinical use. It fell to him to forge ties with commercial partners. "Gus is no cloistered academic," notes Dr. Darrell Kirch, dean of the Penn State's College of Medicine. "He wants this technology to succeed, and he knows that means getting the private sector to run with it."

Besides the 3M partnership, which focused on getting the total artificial heart ready for clinical trials and commercialization, Rosenberg also struck a cooperative agreement in 1993 with Arrow International in nearby Reading, PA. Arrow would work with the Penn State team to refine the wireless electric-powered LVAD design for clinical trials and eventual volume manufacturing.

Both commercial partners initiated extensive testing programs and set about developing production methods consistent with FDA good manufacturing practices. For example, Arrow designed a robotic system that greatly enhanced the quality and consistency of the always troublesome blood sacs. The firm also made design enhancements, such as hermetic seals for the rotor, major changes to the external control system, more compact motor assembly, and improvements in connectors to avoid erosion in the harsh environment of the body. They also sought to make most of the components modular for easier replacement.

Still, every step of the way and in design reviews, the Arrow team leaned heavily on the decades of knowledge represented by Gus Rosenberg and his team. "They are such humble people, yet every time I talk to them I learn something," notes Dan Frank, engineering manager for Arrow's cardiac assist division. "Without the Hershey team, we would not be where we are today."

Surgeons in Europe have been implanting the LionHeart LVAD in clinical trials since 1999, and Arrow hopes to receive Europe's CE mark by this spring. Clinical trials began in the U.S. in February of 2001, and the company is targeting late 2003 or early 2004 for FDA approval. By the end of 2005, there could be as many as 5,000 LionHeart implants worldwide, say company officials.

As Rosenberg sees it, LVADs represent less risk to patients, both in surgery and later on, and can help a broader patient population than total artificial hearts. "With an LVAD, If there is a component failure, a patient can still rely temporarily on his or her own heart until the problem is solved," he explains.

Meanwhile, Penn State's total artificial heart, very similar in concept to the LVAD, also is getting closer to clinical trials. A year after 3M sold its cardiovascular division in 1999, Rosenberg found a new commercial partner for its total heart—former rival Abiomed. "It would have taken enormous resources to move this technology forward on our own," notes Rosenberg, "and Abiomed thoroughly understands this business."

Abiomed made big news in 2001 when surgeons implanted its electro-hydraulic AbioCor™ total artificial heart in five terminally-ill patients under the FDA investigational device exemption program. As a consequence of their sick hearts, the patients also suffered serious pre-operative damage to other vital organs. But the clinical results after surgery were so positive that FDA approved additional clinical trial implants. Clinical trials also will begin in Europe in 2002.

While pushing ahead with its own home-grown technology, Abiomed CEO David Lederman sees the Penn State technology as a valuable complement. "Each device has its advantages," says Lederman, an engineer with many years in heart-assist research. "For a company committed to this field, we need to make sure that the technology we have in our hands is the best. We now have the two best teams in the world working together."

Abiomed is planning to do clinical trials in 2004 featuring a smaller version of the Penn State heart, suitable for women and children. The system features a 50-cc stroke volume pump, versus the 70-cc output of the original Penn State design.

Of Rosenberg, Lederman says: "Gus is one of the primary contributors to this field, and I have tremendous respect for him. We were competitors, but we also have shared a lot of information over the years."

As the years wear on, this sharing of technical advances—always strongly encouraged by NIH—has become more and more important to the teams seeking the elusive goal of designing heart-assist devices that will extend people's lives not just for months but for years. Design teams are exchanging ideas on such areas as materials, control systems, and longer-life batteries. Also being investigated: miniature centrifugal pumps featuring a magnetically-levitated impeller—a design that eliminates contact in moving parts for greater durability.

Over the next five to ten years, research leaders say, there will be room for several devices to meet the varying needs of patients. Dr. Pierce predicts that in another five years, as many as 10,000 to 15,000 devices could be implanted annually.

All this brings bittersweet feelings to Rosenberg. Having turned over his technical "babies" to Arrow and Abiomed for commercialization, he no longer calls the shots. On the other hand, his team is free to pursue future advances in the technology. Then, too, perhaps he'll now have more time for his hobby—building and racing cars—and to mentor engineering graduate students in the new Bioengineering Institute he directs at Penn State Medical School.

For Rosenberg—and for his colleagues in the heart-assist field—it has indeed been a very long journey. Where most engineers complete several design projects a year, it has taken Rosenberg three decades to negotiate the maze of technical problems associated with an entirely new technical creation: an implanted pump to sustain life itself. Says Jack Marlotte, Rosenberg's commercial collaborator for 16 years at 3M Cardiovascular Systems: "Why have we given this technology so much of our careers? It's simple: We want these devices to help people."

A measure of freedom

A measure of freedom

From the late 1970s, Gerson Rosenberg and his Penn State Medical School team have sought to design totally enclosed heart pumps. Not only does this design give patients more freedom of movement, but the absence of wires protruding through the skin also eliminates a frequent source of infection.

The team's total artificial heart and left ventricular assist device (LVAD) both feature a transcutaneous or wireless energy transmission system, as well as many other common design features, including a drive system featuring a roller screw actuator. Here's a look at the key components of the LionHeart™ 2000 LVAD, designed by Rosenberg and his collaborators at Arrow International, and under clinical trial in the U.S. and Europe.

The pump of the LionHeart LVAD features a roller-screw energy converter. Rotation of the electric motor causes motion  of a pusher plate from left to right, compressing a polyurethane blood sac. The motor then reverses to withdraw the plate and allow the blood sac to refill.

Weighing 3.2 lbs, the implanted system consist of the following components:

• Blood pump. Encased within a titanium housing and situated in the patient's abdomen, the 1.5-lb pump assembly consists of a miniature brushless dc motor, a roller screw pusher- plate actuator, smooth polyurethane blood sac, and two tilting disk valves for unidirectional flow. An outlet cannula, made of coated, woven polyester, extends upward from the pump and connects to the aorta. The blood inlet cannula, which connects to the left ventricle, features a sintered outer surface that discourages blood clotting. In this design, the motor turns the nut of the roller screw, which causes linear motion of a circular pusher plate. In systole, the pusher-plate compresses the sac, ejecting the blood through the outlet cannula. In diastole, the motor reverses to withdraw the pusher-plate, allowing the blood sac to refill. Depending on the control setting, the mechanism can pump from 3 to 7 liters of blood per minute.

• Motor controller and internal coil. The system controller is housed within a titanium case with a set of rechargeable nickel cadmium batteries, which serve as an emergency power supply and allow uncoupling of the external power source for up to 40 minutes for personal hygiene or exercise. In tune with the physiological demands of the patient, software in the controller automatically adjusts the pump speed to match the rate that the blood sac is being filled by the heart. Delivering power to the controller is an implanted internal induction coil that receives energy from the external power transmitter coil. The power transfer efficiency is about 80%. A telemetry link in the controller system permits medical personnel to monitor and adjust the implant simply by placing a wand on the skin over the controller. System software then produces readouts on a monitor for such parameters as heart beat rate, percent pump filling, flow rate, and battery status.

• Compliance chamber. Since this is a totally enclosed system, there's a need for a device that shuttles air to and from spaces inside the evacuated chambers of the heart pump during its operation. Otherwise, large pressure differentials will inhibit performance. Consisting of a circular polymer sac, the chamber is replenished with air through a small access port about every four weeks.
  

  Together with its commercial partner, Arrow International, the Penn State team designed the LionHeart to be the first wireless LVAD. Energy is delivered transcultaneously via external and internal coils. Shown here are all the implanted components of the system.

  On the exterior, the patient wears a power transmitter coil placed against the skin and connected to an 8-lb battery pack, which can be placed either in a shoulder bag or waist pack. The power pack accommodates two rechargeable batteries, each providing two to three hours of power. The system's battery charger not only recharges depleted battery packs, but also delivers power from ordinary wall outlets, such as when an individual is asleep.

Heart pumps outperform drugs

Heart pumps outperform drugs

Results of a long-awaited study are providing new proof that heart-assist devices may be a better choice than traditional drug therapy for patients suffering from end-stage congestive heart failure.

The REMATCH study featured the Heartmate 1LVAD, produced by Thoratec. Unlike the totally implanted LionHeart, this pump requires a drive line that penetrates the skin.

Called the REMATCH (Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart failure), the three-year study charted the quality of life and survival rates of 129 U.S. patients who were either too sick or too old to receive heart transplants. On a randomized basis, about half (68 patients) received the HeartMate I, a vented, electric-driven left ventricular assist device (LVAD) manufactured by the California-based Thoratec. The remaining patients received optimal drug therapy.

The results were dramatic: patients with the implanted device had a 52.1% chance of surviving a year, compared to only a 24.7% survival rate for those on medication therapy. Their quality of life was also better, as measured by mobility and emotional health. Moreover, the one-year survival rate was nearly 75% for patients under 60 who received the LVAD. This suggests that the LVAD performance would even be better if cardiologists would recommend the device for younger and less critically-ill patients.

"This study is proof of concept for LVAD technology," says Dr. Eric Rose, the study's chief investigator and chairman of the department of surgery at Columbia Presbyterian Medical Center in New York. "It is no longer a hypothetical question whether a device like this can prolong and enhance life. It is a fact."

"Even though the patients in this group were some of the sickest patients ever studied, this research clearly demonstrated that the LVAD technology works," adds engineer Victor Poirier, who led the design of HeartMate I and was the Design News 1992 Engineer of the Year.

Still, the research, conducted under a cooperative agreement among Columbia University, Thoratec, and the National Institutes of Health, showed that more progress is needed in LVAD durability. The probability of device failure was 35% after 24 months, pointing to the need for improvements in such areas as inflow-valves, connections, and wear parts. Unlike the transcutaneous LionHeart LVAD designed by Penn State and Arrow, the HeartMate I uses a drive line that penetrates the skin. This feature, the study noted, "can become a conduit for bacterial and fungal infection."

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