Patients with untreated obstructive sleep apnea are significantly more likely to have a recurrence of atrial fibrillation than other patients who have undergone successful cardioversion, according to an article in the May 27th issue of Circulation.

According to background information in the article, atrial fibrillation is the most common sustained heart dysrhythmia, affecting more than 2 million Americans. Although cardioversion can convert the heart to normal rhythm and medications can help to maintain normal rhythms, more than 50 percent of patients return to atrial fibrillation within a year.

American researchers enrolled 43 patients with atrial fibrillation and obstructive sleep apnea with 79 control patients who had been treated for atrial fibrillation at the same academic medical center but did not have the sleep disorder. The researchers followed 39 of the 43 dual-diagnosis patients, 27 of whom received no treatment for their sleep disorder or used it inadequately (fewer than 5 times per week) in the year after cardioversion.

Atrial fibrillation recurred in 82 percent of the patients with untreated/undertreated sleep apnea compared with 42 percent of patients who were treated appropriately for the sleep disorder. Among the 79 control patients who did not have obstructive sleep apnea, there was a 53 percent recurrence rate at 1 year.

"Other recent studies have suggested that atrial fibrillation may be more common in patients with sleep apnea," said Virend Somers, M.D., Ph.D., lead investigator of the study. "To our knowledge this is the first study showing that untreated obstructive sleep apnea is associated with an increased risk of recurrent atrial fibrillation, and that the risk is not explained by other conditions but rather appears to be due to the presence of untreated [apnea] itself."

Somers hypothesized about a connection between sleep apnea and vulnerability to recurrence of atrial fibrillation: "In obstructive sleep apnea, the upper part of the airway essentially collapses when people inhale during sleep. To overcome the obstruction, the patient breathes in harder, which generates very high negative pressures that can make the collapse worse. This raises blood pressure, lowers blood oxygen levels and stretches the walls of the atria, making them susceptible to irregular electrical rhythms."

The study results are particularly important because the prevalence of the sleep disorder increases with obesity, which is an American epidemic. Somers noted, "In the general population, the estimated prevalence of significant obstructive sleep apnea is 24 percent for men and 9 percent for women ages 30 to 60 years, and is even higher when associated with obesity or cardiovascular disease such as high blood pressure. Our control group had a high prevalence of obesity, so it is quite likely that many of those 79 control patients actually had undiagnosed -- and therefore untreated -- sleep apnea. Given the high prevalence of obstructive sleep apnea and the emerging epidemics of obesity and atrial fibrillation, our findings of an increased risk of atrial fibrillation in untreated obstructive sleep apnea patients may have implications for both diseases."

Dr. Somers suggests that selected patients with atrial fibrillation should be screened for obstructive sleep apnea because successful treatment may reduce the risk for recurrence of the dysrhythmia. One common and effective treatment for obstructive sleep apnea is use while sleeping of a device employing continuous positive airway pressure.