THURSDAY, March 17 (HealthDay News) -- The promise of stem cell therapy may have gotten a little closer to reality, with researchers reporting that they've used the cells to help shrink hearts that were dangerously swollen after heart attacks.

The approach involves taking stem cells from a heart patient's own bone marrow, then injecting them into the patient's damaged heart.

The result: a significant improvement of heart performance within months, and a significant reduction in both scar tissue and heart size within a year after the initial therapy.

However, the study is small -- a phase one clinical trial involving just eight male patients -- and still described as "experimental." But the research team says that if confirmed in larger trials, the approach could be a big advance over current treatments for this type of enlarged heart.

"The results are very encouraging," said study co-author Dr. Joshua M. Hare, a professor of medicine and director of the Interdisciplinary Stem Cell Institute at the University of Miami Miller School of Medicine. The therapy has "been under development for about ten years, and finally now we are starting to take a big step forward," he said.

But Hare was also quick to note that much more research and time is needed before the novel treatment could become available to patients. "We can't say whether that'll be in three or seven years down the road. It's hard to speculate precisely. But we're talking sometime this decade," he said.

Hare and his colleagues discussed the findings in the March 17 issue of Circulation Research. The study received funding from the U.S. National Institutes of Health, the University of Miami Interdisciplinary Stem Cell Institute and BioCardia, which makes a catheter used in the procedure.

According to the American Heart Association (AHA), heart enlargement can result from a number of health complications, including heart attack, congestive heart failure, and a form of heart muscle inflammation known as cardiomyopathy. Heart valve disease and high blood pressure can also contribute to heart enlargement as a result of heart muscle thickening.

Over 5 million Americans are burdened now with an enlarged heart due to prior heart attack, the AHA says.

Right now, according to the researchers, chronic use of medications and/or heart transplant are the only means of reducing the increased risk for death, disability, and hospitalization that accompanies an enlarged heart.

To test the new stem cell approach, the study team focused on eight men with an average age of 57. All had suffered a heart attack as far back as 11 years prior to their treatment.

The researchers removed the bone marrow cells from each patient's hip bone, Hare said, adding that they either used the whole bone marrow or took the stem cells in the bone marrow to the laboratory, where the cells could grow and expand.

"To inject the cells into the heart," he continued, "we used a special catheter that could be placed in the heart chamber in such a way as to allow us to inject stem cells directly into the damaged part of the heart."

The scientists used two types of stem cells -- mononuclear and mesenchymal. Although it was not clear whether one type of stem cell had more of a beneficial impact on heart health than another, overall the approach produced impressive results.

Three months after stem cell injection into each patient's heart, the team observed significant "functional recovery" in the heart contraction capacity of those heart areas that had experienced previous damage.

What's more, by the one-year point after a single stem cell injection, heart size was found to have diminished by an average of 15 to 20 percent. That reduction, they noted, is roughly three times what's achievable with current therapies. The approach also reduced the presence of scar tissue by an average of more than 18 percent.

The team said the stem cell treatment was well-tolerated with no serious side effects. Hare estimated that the procedure and the cells would cost approximately $10,000 to $15, 000, "not including a hospital fee if one was needed."

According to Hare, the findings may advance the field of stem cell therapy generally. "In fact, we see this as eventually having a broad application, even for patients with non-cardiac conditions," he said. "And certainly for heart patients, this approach appears to be a safe way to get better clinical results and improve on our limited treatment options."

One outside expert agreed that there are currently few effective treatments for patients with enlarged hearts.

"We don't have very much that works right now," said Dr. Murray A. Mittleman, director of the Cardiovascular Epidemiology Research Unit with the Beth Israel Deaconess Medical Center at Harvard Medical School in Boston. "So if this sort of novel treatment improves outcomes that would certainly be helpful. Especially if it helps patients avoid getting to the stage where they would need a heart transplant."

More information

For more on enlarged hearts and heart disease, visit the American Heart Association.