Bonow added: "The findings are interesting but preliminary. The ejection fraction showed a meaningful increase, but they were normal to begin with. We need more time and more information."
The study was funded by the Finnish Academy of Science and Boston Scientific Inc.
Two other studies presented Wednesday in late-breaking sessions at the AHA meeting showed less convincing results. These studies looked at a different population than the Finnish study: patients with chronic scar tissue from a prior heart attack.
The first study involved injecting patients' own skeletal muscle stem cells directly into the heart. The trial, in 23 heart-failure patients, was primarily designed to assess safety, but the researchers also looked at effectiveness.
"These cells are not designed to be heart tissue, but they do contract and have some electrical activity," Bonow explained.
At one year, the procedure proved safe and, the study authors said, resulted in improvements in pumping function and better quality of life.
The study, however, was not "blinded," meaning that any improvements could be due to a placebo effect. Decreases in the heart's size were minimal, Bonow said.
"This doesn't lead anywhere right now," Bonow said.
The study was funded by Mytogen Inc., a biotech company developing cell-based therapies.
The final study, which involved injecting patients' own stem cells into heart scar tissue, found that it did not affect heart muscle functioning.
"It was safe but didn't improve systolic function, didn't reduce infarct size and didn't influence global left ventricular function," said study lead author Dr. Manuel Galinanes, professor of cardiac surgery at the University of Leicester in England.
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