A French study says people with pacemakers suffer from a high incidence of undiagnosed sleep apnea. The study,which looked at 98 patients with pacemakers, found that 57 percent had undiagnosed sleep apnea, WebMD reported.The report,published in Ciruclation:Journal of the American Heart Association,says all potential pacemaker patients should be screened for sleep apnea, which is known to increase risk of cardiovascular disease. Researchers say abnormally slow heart rhythms are common among patients with obstructive sleep apnea.