POSTED: Wednesday, November 7, 2012 - 11:00am
UPDATED: Wednesday, November 7, 2012 - 11:04am
CNN — For years it was thought that most damage from a major heart attack was permanent: Dead tissue turns to scar tissue, leading to the heart muscle's gradual deterioration.
But now, there is growing optimism that stem cell therapy may help patients with damaged hearts return to a fully functional life, based on results from early studies.
Of course, larger studies have to confirm the results and the devil is in the details. Those details were on display in a series of five presentations Tuesday at the American Heart Association conference in Los Angeles.
Most promising was long-term data on 20 patients with severe, long-term heart failure stemming from past heart attacks. These patients not only improved dramatically after receiving an infusion of their own heart stem cells, but continued to get better two full years after treatment.
"That's from just one injection of these cells," says Dr. Roberto Bolli, the lead researcher and chief of cardiology at the University of Louisville. Such improvement is virtually unheard of, he explains. With standard care, "we know that these patients don't get better with time because once you have a scar, you have a scar."
The patients were treated, on average, three and a half years after their heart attack. Two years after the stem cell infusion, scar tissue was reduced by nearly half, the heart muscle was more flexible and pumped blood more efficiently and the patients' quality of life was dramatically improved.
Cardiac stem cells were also used in another study, involving six patients in Japan.
Three other studies presented at the AHA conference tried a different approach, using stem cells derived from bone marrow. These produced more modest benefits.
Two studies experimented with timing: giving stem cell infusions either days or weeks after the heart attack, in an effort to prevent scarring.
In one of those studies, researchers at the University of Miami Miller School of Medicine used bone marrow-derived cells to treat patients whose heart attacks left them with long-term heart trouble. They reported moderate benefits, including better performance on a test of walking endurance.
In perhaps the most significant finding, no one in any of the research projects suffered significant negative effects.
"At this point, we've had almost 3,000 heart patients treated with stem cells worldwide, and had absolutely no report of serious adverse effects," says Bolli. "Stem cells seem to do no harm, and there's certainly a lot of evidence that they are beneficial."
The University of Miami-led study was seen as important because researchers tested an important variation. About half of the 31 patients in the study received an infusion of their own stem cells, while the other half got stem cells from healthy donors.
Dr. Denis Buxton, an official at the National Heart, Lung and Blood Institute (NHLBI), which funded the research, said donor cells offer potential advantages. "One, it simplifies logistics, so a hospital without a cell processing facility can still perform the treatment." That would also reduce the cost.
In addition, Buxton says donated cells are likely to be more robust than cells from heart patients, who tend to be older and have chronic health problems.
"Stem cells are adversely affected by age and diabetes," says Dr. Jay Traverse, an associate professor of medicine at the Minnesota Heart Institute and the University of Minnesota, who presented a study using people's own bone-marrow stem cells. "If you could use cells from a healthy young donor, that would be ideal."
Traverse is now preparing to embark on a multi-center study using donated cardiac stem cells to treat heart attack patients. The project has NHLBI funding and is led by Dr. Eduardo Marban of Cedars-Sinai Medical Center in Los Angeles. Traverse says the approach is promising because cardiac stem cells are naturally programmed to generate new heart tissue. By one estimate, he says, an individual's heart will replace every cell eight times over the course of a lifetime.
In a pilot study of 17 patients, presented last year, Marban used patients' own heart cells to regrow more than a third of lost tissue. Traverse says that if donor cells prove safe --- as they seem to be, based on Tuesday's presentations --- it would open the door to use the treatment much more widely. The first patient will be treated this month.
While acknowledging that questions remain --- about timing, the type of cells to use and the method of delivery, to name a few --- Traverse sounds supremely confident. "In the long run, this is definitely going to work," he says. " In 10 to 20 years, I think we'll be able to change the natural history of a heart attack."