Challenging generations of medical lore, researchers have found striking new evidence that the human heart can repair itself.
Doctors have long assumed that damage from a heart attack or other ailment is irreversible and that the heart cannot regenerate tissue the way other organs can. But that belief has been shaken by recent research.
A team of American and Italian researchers demonstrated last year that heart muscle cells multiply after a heart attack. Now they have shown that in heart transplant patients, primitive cells from the patient travel to the new heart and grow new muscle and blood vessels.
The researchers studied men who received transplanted hearts from women, and discovered male cells in the donated female hearts.
The discovery could help scientists eventually devise treatments to fix bad hearts.
``There have been hints from animal studies that the cells could migrate before, but this is the first demonstration in a human that it is actually possible,'' said John Fakunding of the National Heart, Lung and Blood Institute, which helped pay for the study in Thursday's New England Journal of Medicine.
The researchers found that heart muscle and blood vessels grew rapidly in the new hearts after transplant. They calculated that as much as one-fifth of the donor heart had been rebuilt by the recipient's own cells.
``Clearly this shows that the heart has the ability to regenerate,'' said Dr. Roberto Bolli of the University of Louisville, who wrote an accompanying editorial. ``It could be a milestone discovery if we learn how to exploit this phenomenon for therapeutic purposes to regenerate heart muscle in patients with heart failure.''
The researchers looked for the male Y chromosome in eight female hearts that were transplanted into men. After the heart recipients died, tissue samples were taken from each donor heart and from remnants of the old heart not removed during transplant surgery.
The researchers found evidence of the primitive cells with stem cell characteristics in the remnants of the old hearts, as well as in the donor hearts. The primitive cells from the recipient could also have come through the patient's bloodstream.
``We have the first strong suggestions that the heart has primitive cells _ meaning cardiac stem cells _ which could be used in the future to repair the heart,'' said Dr. Piero Anversa, who led the researchers at New York Medical College in Valhalla, N.Y., and the University of Udine and the University of Parma in Italy.
Stem cells are master cells that transform themselves into certain types of tissue, such as muscle, skin or bone. Doctors believe stem cells could one day be used to replace or fix failing organs.
Anversa said he and his colleagues are working to identify whether a cardiac stem cell exists and whether it can be manipulated to promote heart repair. ``This is the work that we will be doing for the next couple of years,'' he said.
In the meantime, Anversa said his belief that the heart can repair itself is slowly gaining acceptance. ``I think it is going to be more and more difficult to challenge us.'' he said.