CDU

Michael DeBakey joined the faculty of Baylor College of Medicine (Houston, Texas) in 1948, thus launching a research, teaching and surgical career that has produced a broad range of innovative ideas and techniques in cardiovascular therapies.

He is credited with doing the first successful excision and graft replacement of arterial aneurysms and obstructive lesions. He performed the first successful carotid endarterectomy, the aortocoronary bypass with autogenous saphenous vein graft. And he was a pioneer in the development of an artificial heart.

His interest in a developing efficient pump technology to assist operation of diseased hearts goes back "over 30 years," DeBakey told Cardiovascular Device Update, following the first implantation in the U.S. of the DeBakey Ventricular Assist Device (VAD) last month. "I'd been interested in this for a long time," he said, and in 1966 "used a device that I developed in my research laboratory for ventricle assistance in a patient for the first time. I pumped this patient for 10 days."

While the modern counterpart of that early device bears the famed cardiologist's name, he readily acknowledges the cooperative work required in carrying that early concept to successful clinical trials. "About 15 years ago, I did a heart transplant on an engineer at the Johnson Space Center," he said. "He became interested in what we were doing. And I then met some of his engineers and they became interested in working with us on a VAD which I was trying to get to be much smaller, more efficient and safe." That early VAD used two valves to provide unidirectional flow and a chamber, forming a pump DeBakey termed "large and bulky," in part because it was operated by a "pulsatile" system.

NASA's leading-edge materials – such as the use of titanium for the pump body – and its engineering expertise led to the creation of a much smaller pump, with further development carried out by MicroMed (Houston, Texas), a company created to pursue DeBakey's vision.

In its latest generation, the pump is just three and one-half inches long and about one inch in diameter, described by DeBakey as "a little tube that produces an actual flow with only one moving part in it. It's implanted very, very simply into the heart and chest. It requires very little in the way of surgical dissection to put in because it requires so little space." Thus, it can be implanted in smaller individuals, a drawback of larger VAD systems, according to DeBakey.

He described the pump's placement as follows: "There's a canula from the pump that's inserted into the left ventricle cavity and then a Dacron graft attached to the pump and then to the ascending aorta. So you see, it acts as an auxiliary left ventricle. There's an electrical wiring tube connected to the controller that comes out under the skin in the lower abdomen in the right side, attached to a controller and two batteries on a belt." This allows the patient to move about, to leave the hospital, and perhaps even return to work.

A key issue in such a device is maintaining sufficient healthy blood flow through it. He called the DeBakey VAD "very efficient, [with] blood flow of six to 10 liters per minute, using less than 10 watts of power. It ought to be to be a lot cheaper to manufacture and therefore be much more accessible."

Compared to pulsatile-driven pumps that may cost from $75,000 to as much as $100,000, the DeBakey pump could eventually be produced for a third of those figures, he estimates.

Besides the initial implantation in the U.S., the MicroMed DeBakey VAD has been implanted in nearly three dozen patients in Europe, with what he terms "very gratifying results."

How long the VAD can successfully operate and keep a diseased heart working is still unknown, he said. "We don't know what that limit is right now, most of the patients in Europe have had transplants two to four-and-one-half months. I think it can go much longer." Mechanical studies of the device have been in progress for nearly three years, with "no evidence of wear and tear," he noted. And life testing (or reliability) studies have yet to determine the end point of use.

The "gold standard" for VADs is successful bridging to a heart transplant, but the Holy Grail for such a device is to provide the heart enough time to repair itself, and the achievement of that goal could bring DeBakey's career full circle, from repairing the heart to allowing it to repair itself.

Last month's implant of the MicroMed DeBakey VAD in the U.S. was carried out at Methodist Hospital in Houston, giving it a giant step toward FDA clearance that could come early next year, according to Dallas Anderson, president of MicroMed.

The approval sought is for bridge to transplant, but the DeBakey VAD eventually could be combined with other therapeutic approaches that will provide time for the heart to heal itself. "The future of this area will probably be mechanical support which gives rest and assistance to heart muscle, providing some angiogenic factor to allow that muscle to revascularize and regenerate heart," Anderson said.

The heart, of course, is not a static organ but is constantly changing, the molecules of its tissues continuously rebuilding and replenishing themselves. The heart is made up largely of muscle cells, or myocytes,. Anderson explained, and in the very diseased heart, "one of the myocytes is dying, the next one alive, the next one dead. When you give the heart rest with mechanical support, theses muscle cells actually start to rejuvenate. The VAD can help bring more angiogenesis in those areas so the heart has the chance to make that muscle tissue healthier – to build more blood vessels so they can regenerate." That eventuality could be just a few months away, according to Anderson – declining to give specifics but suggesting that this development will be another therapy combined with VAD use.

Until then, the data to gain the first regulatory approval from the FDA – and to convince cardiologists to use the system – will come from the device itself, specifically from the VAD's controller, developed by SeaMed (Seattle, Washington), another part of the team effort credited by Anderson.

While MicroMed got much of the pump technology from NASA engineers, SeaMed created systems for recording and acquiring its data. According to Anderson, that system "in effect is a laptop computer tied to the pump in the OR to see all the operating parameters of the pump, based on the dynamics of the patient." In terms of the next regulatory steps, MicroMed will have to turn the sea of data produced into an understandable model supporting the case for approval. While U.S. implant trials are ongoing, Anderson said MicroMed will file for European CE-marking this month, with the hope of getting to commercialization there by the end of the year.

Meanwhile, Anderson believes that the DeBakey VAD could work to expand the market for this technology in the short term, even before it achieves Holy Grail status. While VADS are used primarily for the most serious, stage 4 or "no option" cases of heart disease, he predicted that they could be most commonly used at stage 3 for those attempting to fend off the final stage.

"The market itself needs to be transformed," Anderson said. "We need to convince cardiologists that there are alternatives to drug therapy, new technologies, ours and others, that will come along and be less problematic," having greater ease of use and minimal complications. "Let's not wait for these [class 3] patients to get into class 4 and these heavy drugs. Let's get them before they progress into class 4. Once you put in a VAD that's not problematic, you provide a blood flow so that the kidneys, liver, and lungs are profused." That market may be from 30,000 to 60,000 patients in the U.S. alone. But Anderson said the key will be to convince cardiologists "that this device can provide better quality of life – long-term quality of life."

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