People with moderate obstructive sleep apnea have a higher risk of sudden cardiac death, researchers reported in the Journal of the American College of Cardiology.

Sudden cardiac death is when the heart unexpectedly stops functioning completely and the person dies. It is the main cause of natural death in the USA, causing approximately 325,000 adult deaths in the country every year. Half of all heart deaths are caused by sudden cardiac death. When a person's heart suddenly stops beating (sudden cardiac arrest), they must be treated immediately with CPR or an automated external defibrillator.

A person has sleep apnea when they stop breathing for at least ten seconds during their sleep five or more times each hour. The patient typically snores, chokes or gasps during sleep, and wakes up drowsy. In the USA, over 12 million people live with obstructive sleep apnea, according to the National Heart, Lung and Blood Institute. Many sufferers are undiagnosed.

The episodes of breathing pauses are called apneas, which literally means "without breath". An apnea is a period during which breathing either stops or is significantly reduced.

Experts say that sleep apnea affects men more than women. However, a Swedish study found that 50% of women have sleep apnea.

Apoor Gami, MD, MSc, FACC, lead author of the study and a cardiologist at Midwest Heart Specialists - Advocate Medical Group in Elmhust, Ill., said:

"The prevalence of obstructive sleep apnea in Western populations is high and will likely only continue to grow given the obesity epidemic and direct relationship between obesity and sleep apnea."

Previous studies have indicated that sleep apnea can eventually lead to heart and cardiovascular problems, including hypertension (high blood pressure), heart attacks and atrial fibrillation.

In this study, researchers set out to determine whether sleep apnea might influence the risk of sudden cardiac death. In their previous study, they had found that patients with sleep apnea had a higher risk of dying from a heart problem between the hours of 10pm and 6am. In the general population, these times are the least likely for sudden cardiac death.

Dr. Gami and team analyzed data on 10,701 patients who were followed for 5.3 years (average) for incidents of fatal or resuscitated sudden cardiac death.

During the 5.3-year period, 142 patients experience sudden cardiac death. The team found that those with 20 apneas per hour, aged 60 years, and with the lowest oxygen saturation level (78%) had the highest risk of sudden cardiac death.

What is low oxygen saturation? This occurs when air is not getting into the lungs, when the sleep apnea patient is asleep and blood oxygen levels fall. The researchers found that when oxygen saturation goes below 78%, the risk of sudden cardiac death goes up by 80%.

The risk of sudden cardiac death does not shift from daytime to night-time hours

The authors stressed that for sleep apnea patients, the risk of sudden cardiac death "does not simply shift from daytime hours to night-time hours, but that their overall risk of sudden cardiac death is higher than people without sleep apnea."

Virend K. Somers, MD, PhD, FACC, senior author on the study and a professor of medicine at Mayo Clinic College of Medicine in Rochester, Minnesota, said:

"Treating sleep apnea in one person can improve the quality of life of both bed partners and may have the added benefit of helping to prevent cardiovascular disease. If the spouse sees the bed partner stop breathing repeatedly during sleep, this is an important clue that he or she probably has sleep apnea."

Researchers from the University of Wisconsin-Madison reported in the journal SLEEP that people with sleep apnea have more than three times the risk of death from any cause compared to the general population.

Written by Christian Nordqvist