A type of stem cell therapy may offer hope to heart attack survivors who face the prospect of continued heart damage, new research shows.

When infused with progenitor bone marrow cells, these patients showed almost double the improvement in the heart's ability to pump blood as did patients who were given a placebo.

The benefit was most pronounced in patients who had had large heart attacks with greater damage to the heart muscle, according to the study, which tracked people who were relatively low-risk heart patients.

There are reasons to be both excited and cautious about the findings, experts says. "It's a very exciting first study, but there are still some things that need to be defined by a greater number of patients," Dr. Timothy Gardner, medical director for the Center for Heart and Vascular Health at Christiana Care Health Services in Wilmington, Del., says at a news conference Sunday at the American Heart Association's annual meeting in Dallas.
 
"It's startling in that the concept works," adds Dr. Robert Bonow, chief of cardiology at Northwestern University in Chicago and past president of the American Heart Association. "We need to study patients who are sicker."

Coronary heart disease is a major cause of death and leads to heart failure. At this point, the treatments available for the condition put a brake on further damage. Progenitor cell therapy, on the other hand, may actually restore function.

The study authors drew a distinction between progenitor cell therapy and stem cell therapy. While similar, stem cells are "early" cells that can develop into any other kind of cell in the body. Progenitor cells, by contrast, have already started to differentiate into specific cells.

"There have been prior studies without control groups which indicated that by opening arteries and infusing stem cells, you could improve heart function," Bonow says. "But we don't know if it was opening the arteries or infusing the stem cells which caused the effect."

And other studies on the subject, while encouraging, were also small.

"Post-myocardial infarction heart failure remains a major problem, despite optimal therapy," says study author Dr. Volker Schachinger, a professor at the J.W. Goethe University in Frankfurt, Germany. "While there have been small feasibility trials where bone marrow progenitor cells improved heart function, so far there have been no large proof-of-concept studies to establish these findings."

The current study, a double-blind, placebo-controlled trial conducted at multiple centers across Europe, was designed to fill that gap.

More than 200 individuals who had had a heart attack were enrolled in the trial. Half of the participants received infusions of their own bone marrow progenitor cells into their hearts while the other half received placebo infusions.

Both groups had similar left ventricular function, a surrogate predictor of a patient's prognosis after a heart attack, at the beginning of the trial: 47 percent in the placebo group and 48 percent in the bone marrow cell group.
After four months, both groups had improved, but the gains were higher in the bone marrow cell group.

Those in the bone marrow group improved 5.5 percent on average, compared with about 3 percent in the placebo group. This translated into a total left ventricular function of 54 percent in the intervention arm versus 50 percent in the placebo arm.

"What determines whether you live or die is ventricular function, and that is better with stem cells," Bonow says. "It's significantly better, but the difference is small."
There was also evidence that participants who had received the progenitor cells had less heart enlargement and improved blood flow reserve in the artery where the heart attack occurred.
 
"The procedure is safe, and may even reduce cardiovascular events," Schachinger says. "This is the first, large proof-of-concept trial that demonstrates the benefit of progenitor cells. Furthermore, it answers additional questions, such as optimal timing, and it identifies those patients who had the most benefit. Thus, intracoronary infusion of bone marrow-derived progenitor cells holds great promise to limit the development of post-infarction heart failures."

And while not enough to start treating patients, it is enough to launch larger-scale studies.
The latest study received partial support from pharmaceutical companies Guidant and Eli Lilly.