Heart failure patients who fit a specific profile can benefit from injection of stem cells delivered directly into their heart muscle, a new study finds.

Patients with mild or moderate heart failure who have high levels of inflammation responded well to the stem cell injections, and experienced a decline in their risk of heart attacks, strokes and heart-related death, clinical trial results show.

Stem cells injected into targeted areas of a failing heart become activated by inflammation and start pumping out beneficial biochemicals, explained lead researcher Dr. Emerson Perin, medical director of the Texas Heart Institute in Houston.

"These cells are little factories of different proteins, cytokines and other products that then have an effect locally on the heart muscle cells," Perin said, adding that the cells also help improve the health of blood vessels both large and small.

For this clinical trial, Perin and his colleagues recruited 537 people suffering from advanced heart failure with reduced ejection fraction, which is when the main pumping chamber in the left side of the heart is significantly weakened.

Half of the patients chosen at random received 150 million stem cells into targeted areas of still-working heart muscle, delivered though 15 to 20 injections in a single procedure, Perin said.

The areas were selected using a mapping system that found places in the heart where electrical activity still occurred but might be hampered by inflammation.

The therapy did not significantly reduce the number of hospitalizations caused by heart failure, but the researchers found that it did improve participants' heart health in other ways during an average 30 months of follow-up:

All patients who got stem cells experienced a 65% reduction in non-fatal heart attacks and strokes.

Participants with high levels of inflammation were 79% less likely to have non-fatal heart attacks or strokes after stem cell therapy.

Stem cell treatment reduced sudden cardiac death by 80% in people with high levels of inflammation and mild heart failure (ordinary physical activity causes fatigue, heart palpitations or shortness of breath).

These results show that a personalized approach with stem cell therapy can help some with heart failure, Perin said.

Doctors have the ability to single out patients with high levels of inflammation and either mild or moderate heart failure, "and then we're using a very precise way of delivering these cells in each individual patient exactly where they need to be placed," Perin said.

The findings were presented Sunday at the American Heart Association's online annual meeting. Research presented at medical meetings is considered preliminary until published in a peer-reviewed journal.

This new clinical trial "is really a promising study to provide further insights into potential subgroups of patients who may hopefully benefit from stem cell therapy," said Dr. Biykem Bozkurt, director of the Winters Center for Heart Failure at the Baylor College of Medicine in Houston.

Bozkurt said future studies should be able to further refine and identify exactly who would most benefit from stem cell therapy among heart failure patients.

"There's always definitely a need to do more research," Bozkurt said.