There's important news for people who suffer from obstructive sleep apnea and sleep-disordered breathing: new research has shown OSA may increase the risk of sudden cardiac death. A large-scale study of more than 10,000 adults over a period of 15 years found obstructive sleep apnea associated with a significantly increased risk of sudden cardiac death.Researchers studied 10,701 adult men and women, all of whom had undergone a polysomnogram to diagnose possible sleep apnea. Among this group, 78 percent were ultimately diagnosed with OSA. The average age of those included was 53 at the study's outset. Researchers followed the participants over the next 15 years, to assess incidents of sudden cardiac events and their possible connection to obstructive sleep apnea. They found:
- Over the 15-year follow up period, 142 people experienced sudden cardiac arrest. In some cases this was fatal, while others were resuscitated.
- Researchers' analysis found people with OSA were at significantly greater risk of sudden cardiac death.
- The three strongest predictors of risk for sudden cardiac death were: being 60 years or older, having low blood oxygen levels, and having at least 20 episodes of apnea per hour.
Apnea episodes occur when, during sleep, muscles at the back of the throat close, temporarily obstructing the airway and interrupting breathing. These episodes, which result in poor and unrefreshing sleep, are the hallmark of OSA. The severity of obstructive sleep apnea is measured by the frequency of apnea episodes, which can vary from a few times to dozens of times in an hour. A rate of 20 episodes an hour is considered moderate sleep apnea.An earlier study conducted by some of the same researchers found that among patients with obstructive sleep apnea, sudden cardiac death frequently occurred at night. This sets these patients strikingly apart from others who suffer cardiac death. For the general population, the risk of sudden cardiac death is greatest during the morning hours. This previous study involved a review of 112 cases of sudden cardiac death in people who had also undergone polysomnography to diagnose possible sleep apnea. Researchers compared the timing of these cardiac events among those with OSA to those in the study without OSA, the general population, as well as to the expectations of chance. They found:
- Between the hours of midnight and 6 a.m., sudden cardiac death occurred in 46 percent of people with OSA, compared to 21 percent of those without OSA, 16 percent of the general population, and 25 percent expected by chance alone.
- People who suffered sudden cardiac death during the hours of midnight and 6 a.m. had more severe sleep apnea than those who experienced sudden cardiac death at other times.
- Analysis revealed that the risk of sudden cardiac death during these overnight hours was directly associated with obstructive sleep apnea.
This study was the first one to establish a directly link between OSA and sudden cardiac death. The current research both confirms and also expands evidence of this connection. Neither of these studies established a cause-and-effect relationship between sleep apnea and sudden cardiac death. But they do indicate a strong association between the two.
More than 18 million Americans suffer from obstructive sleep apnea, according to the National Sleep Foundation. The actual figure may be even higher, since there are strong indications that OSA is seriously under-diagnosed, especially among women. Sudden cardiac death strikes between 180,000 to 450,000 people a year in the United States, according to the American Heart Association. Obesity is a primary risk factor for obstructive sleep apnea, and also puts people at higher risk for sudden cardiac death. The other cardiovascular conditions associated with sleep apnea, including cardiac arrthymias and high blood pressure, also elevate risk for sudden cardiac death. In discussing their results, researchers suggest that the presence of sleep apnea may be a "tipping point" in the accumulation of risk factors for sudden cardiac death.
There's a great deal more to learn about this connection, including whether treatment for OSA, including continuous positive airway pressure therapy (CPAP), is effective in reducing risk for sudden cardiac death among patients with sleep apnea. Research has shown CPAP therapy reduces risk for other cardiovascular conditions, including high blood pressure and heart disease. So there is reason for optimism that similar benefits might extend to the risk of sudden cardiac death.
This news provides yet another reason why it's important not to ignore symptoms of obstructive sleep apnea in yourself or your partner. Snoring, daytime tiredness, and fatigue are among the most common symptoms. If you experience these symptoms, talk to your doctor. Tending to your sleep can help you protect your heart.
Michael J. Breus, PhD
The Sleep Doctor®
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