Severe Sleep Apnea May Almost Double Risk of Sudden Cardiac Death

Marlene Busko

June 12, 2013

ROCHESTER, Minnesota — In an observational study of more than 10 000 adults who participated in sleep studies, being age 60 or older, having moderate or severe sleep apnea, and having severe drops in oxygen saturation while sleeping predicted an increased risk of sudden cardiac death [1]. The risk of sudden cardiac death was almost twice as high in patients who stopped breathing more than 20 times an hour during sleep.

There is no need to panic, however, since sleep apnea is eminently treatable, the study's senior author, Dr Virend K Somers (Mayo Clinic, Rochester, MN), said in a statement. But the findings do suggest that "it would probably be wisest to err on the side of treating people with more severe sleep apnea--20 or more apneas per hour--and nocturnal oxygen desaturation, [and] there is reason to suspect that even [patients with] milder sleep apnea may have other cardiac problems," he told heartwire .

The study, by Dr Apoor S Gami (Mayo Clinic) and colleagues, was published online June 11, 2013 in the Journal of the American College of Cardiology.

Could Sleep Apnea Alone Explain Sudden Cardiac Death?

Previously, the researchers determined that people with sleep apnea are more likely to have sudden cardiac death during nighttime sleeping hours, whereas people without sleep apnea are more likely to die from this cause in the early-morning hours.

Increasing evidence links obstructive sleep apnea with CAD, hypertension, left ventricular dysfunction, and arrhythmias, the group writes.

To investigate the link between sleep apnea and sudden cardiac death, they analyzed data from 10 701 consecutive residents of Minnesota over age 18 who were referred to the Mayo Sleep Disorders Center between 1987 and 2003 for a first polysomnogram, generally to investigate sleep-disordered breathing. Patients were diagnosed as having obstructive sleep apnea if they had five or more episodes of apnea and hypopnea per hour of sleep (apnea-hypopnea index [AHI] >5).

The patients had a mean age of 53 years and a mean body-mass index (BMI) of 34, and 68% were male. They were followed for an average of 5.3 years and up to 15 years. The average rate of fatal or resuscitated sudden cardiac death was 0.27% per year.

A total of 121 patients had fatal sudden cardiac death due to an unidentifiable or nondefinitive cause (58 patients), definite ventricular arrhythmia (44), acute MI (18), or massive pulmonary embolism (1), and 21 patients had resuscitated sudden cardiac death (an implantable cardioverter defibrillator fired or they received advanced cardiac life support).

In multivariate analysis, independent risk factors for sudden cardiac death included age, hypertension, CAD, cardiomyopathy or heart failure, ventricular ectopy or nonsustained ventricular tachycardia, and lowest nocturnal oxygen-saturation levels.

Classification and regression-tree analyses identified the following predictors of sudden cardiac death: age >60 (HR 5.53), AHI >20 (HR 1.60), mean nocturnal oxygen saturation <93% (HR 2.93), and lowest nocturnal oxygen saturation of 78% (HR 2.60, all p<0.0001).

Patients with an AHI of >20 had a 60% increased risk of sudden cardiac death; those whose oxygen saturation dropped below 78% during the sleep test had an 81% increased risk of sudden cardiac death.

Risk of Sudden Cardiac Death

Risk factor HR (95% CI) p
AHI >20 vs <20 1.60 (1.14–2.24) 0.007
Lowest nocturnal O2 saturation 78% vs >78% 1.81 (1.28–2.56) 0.0008

"Notably, the severity of nocturnal hypoxia, which is an important pathophysiological feature of obstructive sleep apnea, strongly predicted sudden cardiac death independently of other well-established risk factors," the authors write.

A cascade of possible biologic mechanisms might explain this relationship. "The repeated episodes of hypoxemia trigger potentially damaging responses that include increases in sympathetic drive and increases in vasoactive substances, which tend to cause marked increases in blood pressure," Somers explained.

Treatments for sleep apnea include weight loss (which helps to decrease the severity of sleep apnea), sleeping on the side (instead of the back), or using a mandibular device or a continuous positive airway pressure device, he said.

Somers has served as a consultant for ResMed, Medtronic, and NeuPro; has received support from a gift from the Phillips-Respironics Foundation to the Mayo Foundation; and is working on intellectual property related to sleep and heart disease with Mayo Health Solutions. Gami has served as a consultant for Medtronic, Boston Scientific, and St Jude Medical. The study was supported by grants from the National Institutes of Health.

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