MONDAY, March 12 (HealthDay News) -- Two out of three people given pacemakers for heart problems were found to have sleep apnea, which could worsen their cardiac disease, French researchers report.

"There have been previous studies that showed a lower prevalence [of sleep apnea] but the sensitivity of the methods used in those studies was insufficient to detect all cases," said lead researcher Dr. Patrick Levy, a professor of physiology at Grenoble University.

In fact, 21 of the 98 pacemaker users who were tested in the study were found to have severe sleep apnea, meaning their breathing was interrupted at least 30 times each hour. That percentage equals that seen in the general population, the researchers said. Their report appears in the March 13 issue of Circulation.

But another 36 of the study participants had more subtle forms of sleep apnea. These conditions were only detected by laboratory monitoring that used polysomnography, a device that records breathing and sleep.

"This is an important clinical finding," Levy said. "They were not as symptomatic as the usual sleep apnea patients. In usual sleep apnea, we are looking for snoring and sleepiness. Most of these patients were not presenting with sleepiness."

In the trial, sleep apnea was defined as abnormally slowed breathing occurring 10 times or more an hour.

A number of studies have linked sleep apnea with a higher risk of cardiovascular conditions such as heart attacks and stroke. For example, one study found that sleep apnea doubled stroke risk.

The new findings didn't surprise one U.S. expert.

"This study basically makes the point that patients who have electrical disease of the heart have a high incidence of sleep apnea," said Dr. Kenneth Ellenbogen, director of the electrophysiology and pacing laboratory at Virginia Commonwealth University and a spokesman for the American Heart Association.

"You shouldn't think that once you put the pacemaker in, you're done," he said. "There are a whole series of things we should be thinking about."

Specifically, doctors should be thinking about testing people who get pacemakers for sleep apnea, Ellenbogen said.

But Levy said his team is "not advocating testing every single pacemaker patient. That is not realistic. We need some simplified way of diagnosis, and the challenge is to provide the medical community with such a tool."

The study could not determine whether sleep apnea was present before the pacemakers were put in or whether it developed afterward, Levy said.

It is possible that treating sleep apnea by such measures as weight loss, cessation of smoking and a technique called continuous positive air pressure (CPAP) could help restore normal heart rhythm for some people, he said. "If you successfully treat the sleep apnea, some patients may not need the pacemaker," he said.

But more studies are needed to determine the best treatment strategy for people who need pacemakers and have sleep apnea, Levy added.

More information

There's more on pacemakers at the American Heart Association.