Using stem cells harvested from patients' own bone marrow, researchers improved cardiac function in heart attack patients months, years -- and even decades -- after the attacks, they reported Wednesday.
The infusion of stem cells boosted cardiac pumping efficiency by 7% in three months -- a modest gain, but still a significant improvement for a chronic condition.
In one case, a patient who had suffered a heart attack 30 years earlier showed an 11% improvement after the treatment, according to the study in the New England Journal of Medicine.
The German researchers also found tentative signs that patients could continue to improve with repeated treatments.
"We have always thought that a heart attack is permanent damage, but now there is the potential that this damage can be repaired," said Dr. Christopher P. Cannon, a cardiologist at Brigham and Women's Hospital in Boston who was not involved in the research.
Though the researchers are uncertain why the therapy works, the findings are a sign that the long-touted regenerative powers of stem cells may be gradually moving from the laboratory into viable human therapies.
Some researchers cautioned that it was too soon to say that the results could be translated into a routine treatment.
"There are a number of therapies that have gotten to this step but when subjected to more rigorous trials have not worked," said Dr. Gregg C. Fonarow, a professor of cardiovascular medicine at UCLA.
But Dr. Andreas M. Zeiher, chair of the department of medicine at Johann Wolfgang Goethe University in Frankfurt and senior author of the study, said the preliminary results pointed to potential new strategies for treating chronic heart disease, for which there is no cure.
Stem cells present one of the most tantalizing mysteries in medicine. One form, known as embryonic stem cells, are capable of generating any type of tissue in the body, but scientists haven't learned the biochemical means to transform them.
The current study focused on a second type of cells known as adult stem cells. There are many types, each focused on regenerating a specific group of tissues to help the body repair normal wear and tear.
Stem cells from bone marrow have been used for decades to regenerate blood and immune cells in cancer patients. Laboratory experiments suggest that these cells also can make heart muscle, blood vessels, nerve cells and other tissues.
