People with chest pain that doesn't respond to regular treatments may benefit from an injection of stem cells into their heart, a new study suggests.

Patients who had the experimental stem cell injections reported half as many episodes of chest pain and performed better on exercise tests than those who got injections of a placebo, U.S. researchers said in Thursday's issue of the American Heart Association journal Circulation Research. The stem cell injections aim to create new vessels in the diseased heart muscle, to improve blood flow to the area and reducing episodes of chest pain. Eric Brady/The Roanoke Times/AP

The study focused on 167 patients with "refractory" angina, or chest pain that persists in spite of medication, surgery or angioplasty.

Researchers used the patients' CD34+ stem cells, which circulate through the blood and are important in forming new blood vessels.

The stem cell injections aim to create new vessels in the diseased heart muscle, to improve blood flow to the area and reduce episodes of chest pain.

Patients were given a drug for several days to increase the number of CD34+ stem cells in the blood.

Blood was collected and processed to collect the stem cells, and then, using a catheter threaded into the heart, the researchers injected the CD34+ cells into diseased areas.

Participants were randomly assigned to low or high doses of the injection or a placebo. They were also given a drug to increase the number of stem cells.

The findings included:

• Six months after the procedure, patients treated with the stem cells had an average of seven attacks of angina a week, compared with nearly 11 in the placebo group.
• At 12 months, the low-dose stem cell patients were having around six chest pain episodes a week, compared with 11 in the placebo-treated patients.
• Exercise tolerance test scores showed greater improvement for the low-dose stem cell group compared to the placebo-treated patients.

"It translates as going from being able to watch television to being able to walk at a normal pace or going from being able to walk slowly to being able to ride a bike," Dr. Douglas Losordo, lead researcher and professor of medicine and director of the Feinberg Cardiovascular Research Institute at Northwestern University in Chicago, said in a release.

Five participants withdrew from the study because of events potentially tied to the procedures, the researchers said, who noted the safety of injection procedure needs to be considered carefully.

The investigators called for larger studies to verify the effects and to refine the methods for collecting and giving the CD34+ cells to patients with disabling angina symptoms.

The study was funded by the medical device manufacturer Baxter Healthcare.