Sleep Apnea Index Misses CV Warning Signs

Clinicians are likely overlooking a handful of significant predictors of cardiovascular risk among older adults with obstructive sleep apnea (OSA), a new study has found.

The apnea-hypopnea index (AHI) is the most frequently used tool for assessing the severity of breathing interruptions that are associated with OSA. The AHI calculates severity by dividing the number of apnea or hypopnea events by the number of hours of sleep (5-15/hour indicates mild OSA; 15-30/hour indicates moderate OSA; and >30/hour indicates severe OSA).

However, according to the results of a recent cohort study, relying on this tool alone may exclude other important aspects of a patient’s clinical picture. A team of Canadian researchers examined data of more than 10,000 adults with suspected OSA. Over an average follow-up period of 6 years, 11.5% of the participants had been hospitalized for myocardial infarction, stroke, or congestive heart failure, underwent a revascularization procedure, or died from any cause.

Information about the participants’ OSA-related symptoms was gleaned from a database of polysomnography results at a Canadian hospital, where these patients had been referred for OSA treatment. After adjusting for multiple established risk factors for cardiovascular disease, including smoking and age, using Cox regression models, the researchers found several variables related to OSA that significantly predicted cardiovascular risk—the AHI was not one of them.

Total sleep time spent with an arterial oxygen saturation value below 90% was the strongest predictor (9 minute vs 0 minutes, hazard ratio=1.5; 95% confidence interval, 1.25-1.79). The relative risk associated with this value ranged from 5% to 50%, after controlling for known cardiovascular risk factors. Other variables reached statistical significance as well, including total sleep time, number of awakenings, frequency of period leg movements, heart rate, and self-reported daytime sleepiness.

Although the AHI was significantly associated with a composite cardiovascular outcome when analyzed by itself, the association did not remain statistically significant after adjusting for confounders.

The authors acknowledged the limitations of their study, including the fact that they did not have information about patients’ adherence to continuous positive airway pressure, which is often recommended for patients with severe OSA.

Despite these limitations, the authors concluded “OSA-related factors other than AHI were shown as important predictors of composite cardiovascular outcome and should be considered in future studies and clinical practice.”

- Allison Musante, ELS

Reference

Kendzerska T, Gershon AS, Hawker G, Leung RS, Tomlinson G. Obstructive sleep apnea and risk of cardiovascular events and all-cause mortality: a decade-long historical cohort study. PLoS Medicine. 2014;11(2). Published online February 4, 2014.