New research published online in the Journal of the American College of Cardiology indicates that sleep apnea raises the risk of sudden cardiac death. To investigate the link between sleep apnea and sudden cardiac death, a long-term study funded by the U.S. National Institutes of Health analyzed data from 10,701 consecutive residents of Minnesota over age 18 who were referred to the Mayo Sleep Disorders Center between 1987 and 2003 for a first polysomnogram, generally to investigate sleep-disordered breathing. Patients were diagnosed as having obstructive sleep apnea if they had five or more episodes of apnea and hypopnea per hour of sleep. "The presence and severity of sleep apnea are associated with a significantly increased risk of sudden cardiac death," said study leader Dr. Apoor Gami, a cardiac electrophysiologist at Midwest Heart Specialists-Advocate Medical Group in Elmhurst, Illinois. Sudden cardiac death kills 450,000 people a year in the United States, according to study background information. It occurs when the heart unexpectedly and suddenly stops beating due to problems with the heart's electrical system. Those problems cause irregular heartbeats. The condition must be treated within minutes if the person is to survive. In earlier research, Gami and his team had found that patients with sleep apnea who suffered sudden cardiac death often did so at night, a completely opposite pattern than found in others without sleep apnea who had sudden cardiac death. "That was the first direct link (found) between sudden cardiac death and sleep apnea," Gami said. Three measures strongly predicted the risk of sudden cardiac death, he added. These include being 60 or older, having 20 apnea episodes an hour or having low blood levels of oxygen. This oxygen saturation drops when air doesn't flow into the lungs. "If the lowest oxygen saturation was 78 percent, or less, their risk of (sudden cardiac death) increased by 80 percent," Gami said. In a healthy person, 95 percent to 100 percent is normal. Having 20 events an hour would be termed moderate sleep apnea, Gami said. Gami found a link, not a cause-and-effect relationship, between sleep apnea and sudden cardiac death. He can't explain the connection with certainty, but said there are several possible explanations. For example, sleep apnea is related to the type of heart rhythm problem that causes sudden cardiac death, he said. The study didn't address whether those who used sleep apnea treatments would reduce risk. "It would be fair to say we suspect it would," Gami said.