Research Offers New Hope for Heart Bypass Patients

Pacemakers could become obsolete, another study suggests

SUNDAY, Nov. 17, 2002 (HealthDayNews) -- Two new engineering feats may one day brighten the prospects for cardiac bypass patients and other heart patients.

Both studies were reported today at the American Heart Association's annual meeting in Chicago.

In the first study, researchers used tissue engineering to build blood vessels from human skin cell tissue, then implanted them into laboratory animals, where they worked well for up to two weeks.

If the results are borne out in human trials, (which the scientists hope to begin by the start of 2004), this could be good news for people who need to undergo heart and leg bypass operations, among other procedures.

Past attempts at this type of engineering had had to use scaffolds made of synthetic materials, which ran the risk of being rejected by the body. The process used in the new study required no such scaffold.

"The technology that we're working on is the capability to grow blood vessels exclusively from your own cells, and that's what separates us from any other technology," says Todd McAllister, co-author of the study and president and CEO of Cytograft Tissue Engineering in Novato, Calif., which developed the technique. "Others depend on the presence of a scaffold."

McAllister and his colleagues took skin cells from 11 patients aged 54 to 84, all of whom had advanced cardiovascular disease and who were undergoing coronary artery bypass operations. The cells were harvested and expanded, then grown into a sheet of cells.

"That sheet is like carbon fiber or some cloth material from which you can assemble more complex three-dimensional structures," McAllister explains. "We roll the sheet around a temporary support and essentially make a jelly roll of tissue. It then goes through the maturation phase where it fuses together to form a homogenous tissue." The process takes about 12 to 14 weeks.

The newly formed vessels were implanted as a leg artery graft in four study animals, and were removed at three, seven or 14 days, depending on the animal. Three of the four grafted vessels survived past the third day, without developing any blood clots. The vessels were also strong and resilient, smaller than had been achieved in the past, and came from an array of patients, meaning that the same procedure could work for different people, McAllister says.

But there's still a long way to go before the technique can be used on humans.

Dr. Jacob Shani, director of cardiology at Maimonides Medical Center in Brooklyn, N.Y., who was not involved in the McAllister research, says, "The concepts that we are talking about [in the new study] are not new. People have tried, and are still trying, to grow tissue from stem cells. But obviously we're not there yet. It's exciting, but I wouldn't book the procedure yet."

The procedure developed by McAllister's company doesn't involve stem cells, but actual human cells.

"The problem starts when you compare it to what's already available," Shani continues. "We have blood vessels from our bodies, veins we use in bypass and these are readily available in most patients. You cut from one place and put it in another. You have to bring something that will beat it because the cost is obviously far greater."

Although promising, 14 days is a very short time period and, Shani points out, "you're talking about an animal model that doesn't have all of the other complexities that human beings have. The concept is very exciting, but it has to pass the test in human beings."

In the second study, skeletal muscle cells that were implanted into the hearts of lab animals were actually able to connect with existing cells and start passing electrical signals. Though extremely preliminary, the findings may one day provide an alternative for pacemakers.

Myoblasts, or immature skeletal muscle cells, make the same protein that heart muscle cells use to connect with each other and transmit electrical signals. In the study, researchers extracted myoblasts from rats and used them to create three-dimensional strips of tissue that were then surgically implanted into rat hearts.

"We had a theoretical weakness which is that, normally in skeletal muscles, when these cells differentiate, they stop expressing the proteins that are important for electronically and mechanically coupling to each other," says Doug Cowan, lead author of the study and an assistant professor of anesthesiology at Harvard University School of Medicine.

"We didn't know if they were going to behave differently, but they did express the proteins that are necessary for continued mechanical and electrical coupling which was one hurdle. The other was, once transplanted, could they survive. And ultimately they did work."

The idea was originally conceived for children, who have an especially difficult time with pacemakers.

"We're a long, long way away from humans," Cowan says. "We were just sort of testing whether this idea would even be feasible. The results so far have been pretty promising."

Shani, of Maimonides Medical Center, says the researchers behind the second study "were able to achieve connections, which is interesting. It is a wonderful concept.

"Again, it works in the lab. We have to see how it works in humans. But, if indeed, you can establish an electrical connection and then avoid the need for a pacemaker, that will be a phenomenal thing," Shani adds.

What To Do

For more on heart bypass surgery, visit the National Library of Medicine. And check the American Heart Association for more research from Scientific Sessions 2002.

SOURCES: Todd McAllister, Ph.D., president and chief executive officer, Cytograft Tissue Engineering, Novato, Calif.; Jacob Shani, M.D., chairman, Cardiac Institute, and director of cardiology, Maimonides Medical Center, Brooklyn, N.Y.; Douglas B. Cowan, Ph.D., research associate in anesthesia, Children's Hospital, and assistant professor of anesthesia, Harvard University School of Medicine, both in Boston; Nov. 17, 2002, presentations, American Heart Association Scientific Sessions 2002, Chicago
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