Taking Skeletal Muscle to Heart
Weiss, Rick, Science News
Taking Skeletal Muscle to Heart
"Would you have your songs endure? Build on the human heart," advised Robert Browning in the mid-1800s.
Day in, day out, the human heart endures -- leaving physiologists, as well as poets, marveling at its dependability. No other type of muscle has the stamina of that fist-sized, four-chambered pump.
But the heart can fail. and medical researchers who deal with failing hearts are now taking Browning's advice: Rather than replace an injured heart with a mechanical device or a transplant, they are learning how to build on the human heart.
For building materials, they rely mostly on skeletal muscles taken from elsewhere in the body. Using a variety of approaches -- only a few of which have been tried on humans -- scientists increasingly are finding that skeletal muscle can be wrapped around a damaged or overworked heart and rhythmically stimulated to provide valuable assistance. Indeed, while skeletal muscle may never match the heart for its ability to inspire lilting couplets, scientists can now train even the most mundane contractile tissues to do much of the work that was once considered the heart's exclusive domain.
"There's a tremendous clinical need to treat patients with 'end-stage' or irreversible heart failure," says Stephen F. Badylak, who specializes in the use of skeletal muscle for cardiac assistance at Purdue University in West Lafayette, Ind. Each year, he notes, 400,000 people in the United States develop end-stage heart failure -- a serious weakening of the heart due to the death of some portion of cardiac muscle. Nearly half these individuals die within one year.
About 30,000 to 50,000 U.S. heart-failure patients could have benefited from heart transplants last year, but because of the shortage of donors, only 1,400 received them, Badylak says. And scientists developing artificial hearts, although perennially optimistic, remain plagued by a variety of problems -- including the risk of infection from body tubes connecting the device to its external power supply.
"I don't think this will replace the field of artificial heart development, nor will it at this time replace transplantation," says George J. Magovern, the only person to perform the experimental surgery on humans in the United States." But it's a third modality we're looking at, and one that could help a tremendous number of people."
Four of Magovern's five cardiac-assist patients remain alive -- including the first, operated on three years ago (SN: 5/3/86, p.284). Their failing hearts are now securely wrapped in skeletal muscle "blankets." A pacemaker stimulates these living blankets to contract in unison with the heart, taking some of the workload off the tired organ.
"The advantages of using [a patient's] skeletal muscle are obvious," says Badylak, a research physician at Purdue's Hillenbrand Biomedical Engineering Center, which last month hosted a conference on cardiac assistance with skeletal muscle. "It's readily available, and in most cases you have a very willing donor; you don't have to worry about immunosuppression [necessary with transplants] and its attendant infection problems; and there ae no tubes going into the body to increase the chances of infection."
But problems do occur, he and others note. For one thing, Badylak says, "skeletal muscle is not like heart muscle that beats every day and night all the time without stopping. Skeletal muscle gets tired and needs a rest."
Experiments have been performed on dogs with drag-induced heart failure for more than 30 years, says John D. Mannion of the Thomas Jefferson University in Philadelphia. However, he says, until the 1980s -- and sometimes still today -- skeletal muscle "used to last five minutes, then fizzle out."
In part, says Mannion, this muscle failure has been due to the extreme rigors of the experimental surgery. "Part of the problem is that we expect skeletal muscle to do things that we'd never expect cardiac muscle to do. …