Doctors once thought that the holes served as new blood channels. But this idea has been largely rejected, since the holes quickly fill in after the treatment. Proponents now say they think it works by prompting the heart to improve its own blood supply. They say the drilling probably triggers the release of growth proteins, and these force the muscle to sprout new blood vessels, which carry in oxygen and relieve the pain. Another idea is that the damage caused by the laser destroys nerves in the heart.
Pain goes away, even though the underlying problems remain.
However, during a session at the heart meeting, Dr. David Faxon of the University of Chicago raised another often-mentioned possibility. The patients knew they were undergoing a major procedure that doctors believed would help them. Perhaps, the thinking goes, the patients simply imagined their improvement. Such illusions are common in medicine, especially with treatments intended to stop pain. Recently doctors tested a competing form of the treatment that uses a laser on a tube threaded into the heart to drill holes from the inside out.