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OSA identified as novel risk factor for sudden cardiac death

Sunday, November 16 2008 | Comments
Evidence Grade 7 What's This?

By Selma Kaszczuk

Obstructive sleep apnea (OSA) is an independent predictor of sudden cardiac death (SCD), Dr. Apoor Gami of Midwest Heart Specialists in Elmhurst, Ill., reported, and nocturnal hypoxemia, a hallmark characteristic of OSA, strongly predicts SCD independent of other well-established risk factors.

Dr. Gami explained that a number of acute events occur during obstructive apneic sleep, such as hypoxemia, hypercapnia, and fluctuations in intrathoracic pressure. Several investigations have addressed the relationship between OSA and adverse cardiac and vascular conditions, he pointed out, but very little research is available examining its association with SCD.

The present study included 10,701 consecutive adults (mean age, 53 years; 68% male) with no prior history of resuscitated SCD or OSA who underwent a diagnostic polysomnography between 1987 and 2003. In general, those referred for sleep studies did not represent "a sick population," Dr. Gami remarked, as only 14% had coronary artery disease (CAD), 6% congestive heart failure, and <0.5% had a history of ventricular arrhythmia.

A diagnosis of OSA was made if the AHI was >=5, according to criteria from the American Academy of Sleep Medicine. In all, 73% of the evaluated cohort received an OSA diagnosis.

During a mean follow-up of 5.3 years, the study's primary endpoint of fatal or resuscitated SCD occurred in 142 patients, translating to an annual SCD incidence of 0.25%. Dr. Gami said the estimated SCD incidence in the United States is 0.1% to 0.2%, which suggests an incidence that is "slightly higher in the referral population."

In addition to factors including age, hypertension, CAD, heart failure, and ventricular ectopy, multivariate analysis identified lowest nocturnal oxygen saturation as an independent risk factor for SCD, such that for every 10% decrease in oxygen saturation, the risk for SCD significantly increased 10%. In particular, patients who had lowest nocturnal oxygen saturation <=78% had an 81% increase in the risk for SCD independent of any other variable.

"In a group of patients presumably at low risk of SCD, the severity of OSA … strongly and independently predicted the risk of SCD," Dr. Gami said. He provided an OSA prevalence estimate of 20% in the general population, a figure he said was based on older data. "With the growing epidemic of obesity, you would expect that the prevalence of OSA in American [individuals] is actually higher." (Abstract Oral Session 505.)

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