Key Point

Persons with obstructive sleep apnea have a much greater risk of sudden death from cardiac causes during the sleeping hours than does the general population.

ROCHESTER, MINN—Among the general population, the risk of sudden death from cardiac causes is highest between 6 AM and noon. Not so for people with obstructive sleep apnea (OSA), however. They are at greatest risk of sudden death from cardiac causes between midnight and 6 AM—the time of lowest risk for those without OSA.

Apneic episodes result in hypoxemia, hypercapnia, and increases in sympathetic drive, blood pressure, and cardiac wall stress—all of which run counter to the physiology of normal sleep. Researchers from the Mayo Clinic in Rochester, Minnesota, reviewed the death certificates of 112 Minnesota residents—78 of whom had OSA—who underwent polysomnography testing and later died suddenly from cardiac causes.¹

Patients underwent polysomnography between July 1, 1987, and July 31, 2003. The apnea-hypopnea index (AHI) was calculated as the sum of apneas and hypopneas per one hour of sleep. According to the American Academy of Sleep Medicine, an AHI of 5 or more is required for a diagnosis of OSA. Demographic information, height, weight, and coexisting conditions were recorded at the time polysomnography was performed. The use of continuous positive airway pressure (CPAP) was also noted.

The incidence of sudden death from cardiac causes was also recorded for the 34 men and women without OSA.

The groups with and without OSA were similar in age, body mass index, and coexisting conditions. The only difference was that there were more men in the OSA group (82%) than in the non-OSA group (62%). The use of CPAP increased with the AHI; it was used in 58% of patients with an AHI of 40 or more.

RISK OF SUDDEN DEATH HIGHER DURING SLEEPING HOURS

Between midnight and 6 AM, the frequency of sudden death from cardiac causes was significantly higher in patients with OSA—46%—versus 21% in those without OSA. This difference was even more striking when those with OSA were compared to the general population (46% vs 16%).

Interestingly, between 6 AM and noon, the frequency of sudden death from cardiac causes was significantly lower in patients with OSA than in those without (20% vs 41%, respectively). The same held true between noon and 6 PM (9% in patients with OSA vs 26% in those without).

The median AHI of those who died from cardiac causes between midnight and 6 AM was significantly higher than that of those who died between 6 AM and noon (39 vs 8, respectively) and those who died between noon and 6 PM (39 vs 11, respectively). Compared to those without OSA, patients with OSA had a relative risk of sudden death from cardiac causes between midnight and 6 AM of 1.87, and compared to any other time of day, of 2.57 (Table).

In this study, the risk of sudden death during the sleeping hours increased with OSA severity and was 40% higher in those with severe OSA compared to those with mild to moderate or no OSA. The authors pointed out that because the mean age of both groups was around 70, their results cannot be extrapolated to apply to younger patients with OSA.

“The unique day–night pattern of sudden death from cardiac causes that we observed in persons with [OSA] is consistent with their exposure during sleep to critical mechanisms that could promote sudden death from cardiac causes,” the investigators observed. These include the OSA-induced nocturnal changes in blood pressure, oxygen levels, and heart rhythm.

WHAT ABOUT CPAP?

That CPAP may have been ineffective is suggested by the increased incidence in sudden death among patients with severe OSA—even though this group also had the highest rate of CPAP use (58%). The authors cautioned, however, that the lack of objective data from CPAP devices must be taken into account. Compliance with CPAP therapy is also an issue: Patients are often given CPAP devices but do not necessarily use them consistently.

“Our study cannot address the question of whether [OSA] increases the overall risk of sudden death from cardiac causes,” noted the authors. “Given our findings and the relatively high prevalence of [OSA] in the Western populations, this is an important question that remains to be answered.”

—Gale Jurasek

Reference
1. Gami AS, Howard DE, Olson EJ, Somers VK. Day–night pattern of sudden death in obstructive sleep apnea. N Engl J Med. 2005;352:1206-1214.

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