MONDAY, Feb. 13 (HealthDay News) -- Stem cell therapy's promise for healing damaged tissues may have gotten a bit closer to reality. In a small, early study, heart damage was reversed in heart-attack patients treated with their own cardiac stem cells, researchers report.

The cells, called cardiosphere-derived stem cells, regrew damaged heart muscle and reversed scarring one year later, the authors say.

Up until now, heart specialists' best tool to help minimize damage following a heart attack has been to surgically clear blocked arteries.

"In our treatment, we dissolved scar and replaced it with living heart muscle. Such 'therapeutic regeneration' has long been the holy grail of cell therapy, but had never been accomplished before; we now seem to have done it," said study author Dr. Eduardo Marban, director of the Cedars-Sinai Heart Institute in Los Angeles.

However, outside experts cautioned that the findings are preliminary and the treatment is far from ready for widespread use among heart-attack survivors.

The study, published online Feb. 14 in The Lancet, involved 25 middle-aged patients (average age 53) who had suffered a heart attack. Seventeen underwent stem cell infusions while eight received standard post-heart attack care, including medication and exercise therapy.

The stem cells were obtained using a minimally invasive procedure, according to the researchers from Cedars-Sinai and the Johns Hopkins Hospital in Baltimore.

Patients received a local anesthetic and then a catheter was threaded through a neck vein down to the heart, where a tiny portion of muscle was taken. The sample provided all the researchers needed to generate a supply of new stem cells -- 12 million to 25 million -- that were then transplanted back into the heart-attack patient during a second minimally invasive procedure.

One year after the procedure, the infusion patients' cardiac scar sizes had shrunk by about half. Scar size was reduced from 24 percent to 12 percent of the heart, the team said. In contrast, the patients receiving standard care experienced no scar shrinkage.

Initial muscle damage and healed tissue were measured using MRI scans.

After six months, four patients in the stem-cell group experienced serious adverse events compared with only one patient in the control group. At one year, two more stem-cell patients had a serious complication. However, only one such event -- a heart attack -- might have been related to the treatment, according to the study.

In a news release, Marban said that "the effects are substantial and surprisingly larger in humans than they were in animal tests."

Other experts were cautiously optimistic. Cardiac expert Dr. Bernard Gersh, a professor of medicine at Mayo Clinic, is not affiliated with the research but is familiar with the findings.

"This study demonstrates that it is safe and feasible to administer these cardiac-derived stem cells and the results are interesting and encouraging," he said.

Another specialist said that while provocative and promising, the findings remain early, phase-one research. "It's a proof-of-concept study," said interventional cardiologist Dr. Thomas Povsic, an assistant professor of medicine at the Duke Clinical Research Institute, in Durham, N.C.

And Dr. Chip Lavie, medical director of Cardiac Rehabilitation and Prevention at the John Ochsner Heart and Vascular Institute, in New Orleans, also discussed the results. He said that while the study showed that the cardiac stem cells reduced scar tissue and increased the area of live heart tissue in heart attack patients with moderately damaged overall heart tissue, it did not demonstrate a reduction in heart size or any improvement in the heart's pumping ability.

"It did not improve the ejection fraction, which is a very important measurement used to define the overall heart's pumping ability," Lavie noted. "Certainly, much larger studies of various types of heart attack patients will be needed before this even comes close to being a viable potential therapy for the large number of heart attack initial survivors."

Povsic concurred that much larger studies are needed. "The next step is showing it really helps patients in some kind of meaningful way, by either preventing death, healing them or making them feel better."

It's unclear what the cost will be, Povsic added. "What society is going to be willing to pay for this is going to be based on how much good it ends up doing. If they truly regenerate a heart and prevent a heart transplant, that would save a lot money."

Marban, who invented the stem cell treatment, said the while it would not replace bypass surgery or angioplasty, "it might be useful in treating 'irreversible' injury that may persist after those procedures."

As a rough estimate, he said that if larger, phase 2 trials were successful, the treatment might be available to the general public by about 2016.

More information

The U.S. National Heart, Lung, and Blood Institute describes current heart attack treatment.