People with sleep apnea have a slightly higher risk for sudden cardiac arrest (SCA) — an often fatal condition when the heart shuts off — according to a study from the Mayo Clinic published today.

Sudden cardiac deaths account for nearly half a million deaths per year, but their underlying risk factors remain unresolved.

A growing body of evidence suggests that sleep apnea, where a person's breathing pauses or becomes shallow while asleep, increases a person's chances for developing heart disease.

This same group of Mayo researchers found people with sleep apnea had 2.6-fold higher risk of SCA while sleeping during the night — between 10 p.m. and 6 a.m. In the general population, these hours are typically connected with the lowest number of sudden cardiac deaths.

"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," said lead author Dr. Apoor Gami, M.D., MSc, FACC, a cardiologist at Midwest Heart Specialists - Advocate Medical Group in Elmhust, Ill.

This study recruited 10,000 Minnesota residents with suspected sleep disorders and identified 78 percent with moderate sleep apnea. Patients were tracked for up to 15 years, although the average follow-up occurred five years after an initial overnight sleep exam.

During the study period, 142 subject had a fatal SCA or required resuscitation via CPR or automated external defibrillator (AED), which amounts to an overall risk of 0.27 percent. This is only a marginal elevation relative to SCA in the general population (0.1 - 0.2 percent), but given one in five adults suffer from at lease mild sleep apnea, it could equate to hundreds of thousands of people having a higher risk for the condition.

The researchers, moreover, found that in individuals with the most severe sleep apnea, where their oxygen levels drop below 78 percent of normal, risk for sudden cardiac death goes up by 80 percent.

Low oxygen ties into the rationale for why sleep apnea is so dangerous to the heart. During eight hours of sleep, the affliction can stop a person from breathing for up to 40 times for 10 seconds or longer. The body's organs respond to the oxygen interruptions by demanding more blood, which places extra strain on the heart during a time when it is normally resting. Less oxygen in the body can also choke the heart and increase variability in heart rate.

Along with prior studies that have linked sleep apnea to high blood pressure, irregular heart beats, and heart attacks, this study provides further support to the idea that sleep apnea factors into heart disease.

Assistive breathing devices or surgery to remodel air passages can remedy sleep apnea.

"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," said senior author Dr. Virend K. Somers, M.D., a professor of medicine at Mayo Clinic College of Medicine in Rochester, Minn. "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."

Sleep Apnea Increases Risk of Sudden Cardiac Death

Credit: American College of Cardiology

Sources: Gami AS, Olson EJ, Shen WK, et al. Obstructive Sleep Apnea and the Risk of Sudden Cardiac Death: A Longitudinal Study of 10,701 Adults. Journal of the American College of Cardiology. 2013.

Gami AS, Howard DE, Olson EJ, Somers VK. Day-Night Pattern of Sudden Death in Obstructive Sleep Apnea. NEJM. 2005.