Is Snoring a Risk Factor for Stroke?
Abstract and Commentary
By Matthew E. Fink, MD, Vice Chairman, Professor of Clinical Neurology, Weill-Cornell Medical College, Chief, Division of Stroke and Critical Care Neurology, NewYork-Presbyterian Hospital. Dr. Fink reports no consultant, stockholder, speaker's bureau, research, or other financial relationship with any company related to this field of study.
Synopsis: In a prospective cohort study of 697 patients with obstructive sleep apnea followed for a median duration of 3.4 years, there was a significant association with stroke or death (adjusted hazard ratio, 1.97; 95% CI, 1.12-3.48; P = 0.01).
Source: Yaggi HK, et al. Obstructive Sleep Apnea As a Risk Factor for Stroke and Death. N Engl J Med. 2005;353:2034-2041.
As the second leading cause of death worldwide, and the leading cause for permanent disability, ongoing efforts to identify modifiable risk factors to reduce the burden of stroke has taken on great importance. Neurologists have long suspected that obstructive sleep apnea is associated with an increased risk of stroke but, until now, there was no strong epidemiological evidence to confirm these suspicions. In addition, it was never clear whether obstructive sleep apnea was a cause or consequence of stroke.
Yaggi and colleagues at Yale performed a prospective, observational cohort study of 1022 patients who were referred for evaluation of sleep-disordered breathing. The exposure group was defined as patients over age 50, having 5 or more apnea-hypopnea events per hour of sleep; patients with less than 5 events per hour constituted the comparison group. Patients were excluded from the study if they had any prior history of stroke, myocardial infarction, or tracheostomy. Other risk factors, including hypertension, atrial fibrillation, diabetes mellitus, or hyperlipidemia, were noted. A single, overnight polysomnographic study was conducted, and sleep stages were scored according to standard criteria. Patient follow-up was performed by questionnaire and telephone call to identify a first stroke or death, and any reported event was confirmed by review of medical records.
A total of 697 of the 1022 study participants (68%) were classified as having obstructive sleep apnea syndrome, and they were followed for a median duration of 3.4 years (interquartile range, 2.8-4.2), with the remainder followed as the comparison group. Complete follow-up information was obtained for 842 patients (82%). Incident stroke or death from any cause occurred in 88 patients (9%), and included 22 strokes and 50 deaths in the group with obstructive sleep apnea as compared with 2 strokes and 14 deaths in the comparison group. Even after adjusting for all other stroke risk factors, the obstructive sleep apnea syndrome retained a statistically significant association with stroke or death (hazard ratio, 1.97; 95% CI, 1.12-3.48; P = 0.01).
The Yale group has provided us with strong and compelling data that support our suspicions that obstructive sleep apnea is a significant and powerful risk factor for stroke or death. Prior to this study, it was unclear if the suspected association was due to other associated risk factors such as obesity and hypertension. However, even after adjusting for these risk factors, obstructive sleep apnea remains a significant and independent risk factor for stroke or death.
Obstructive sleep apnea results in a number of physiologic derangements that could increase the risk of stroke, including decreased cerebral blood flow, hypercoagulability, occult paroxysmal atrial fibrillation, paradoxical embolism, hypoxia-related cerebral ischemia, and accelerated atherosclerosis. It seems clear that this syndrome is a significant risk factor for stroke, and neurologists should consider and evaluate those patients at risk who report loud snoring that is frequent or continuous. Once diagnosed, we need to determine if successful interventions, such as continuous positive airway pressure during sleep, will help reduce the risk of stroke or death. Hopefully, we have identified another modifiable risk factor that will help us in the primary and secondary prevention of stroke and other cardiovascular diseases.