Patients with severe sleep-disordered breathing are two to four times more likely to experience complex, abnormal heart rhythms while sleeping than individuals without the problem, according to the Sleep Heart Health Study (SHHS).

These findings appear in the April 15 issue of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

Reena Mehra, M.D., M.S., of University Hospitals of Cleveland at Case Western Reserve University in Ohio, and seven associates compared the prevalence of arrhythmias in 228 patients with sleep-disordered breathing and 338 with no sleep disorder. The individuals in both groups participated in the SHHS, a multi-center longitudinal study of designed to determine the cardiovascular consequences of sleep-disordered breathing (SDB).

SDB is an illness in which a sleeping individual repeatedly stops breathing for 10 seconds or longer before resuming air intake. These stoppages decrease the amount of oxygen and increase the level of carbon dioxide in the blood and brain. In this study, participants with SDB had a respiratory disturbance index that averaged about 44 pauses per hour of sleep. The control subjects experienced only 2.8 interruptions per hour.

“Individuals with sleep-disordered breathing had four times the odds of atrial fibrillation and three times the odds of nonsustained ventricular tachycardia,” said Dr. Mehra.

Atrial fibrillation consists of very rapid contractions of the atria (the upper chambers of the heart), leading the ventricles (the lower chambers of the heart) to beat irregularly. This results in decreased heart output and potential for clot formation. Tachycardia is defined by abnormally rapid heart beats - over 100 beats per minute in an adult.

“Consistent with the study design, no sex or race differences were observed between groups,” said Dr. Mehra. “However, the SDB group was modestly older and had a higher body mass index than the control patients.” She added that arrhythmias generally tended to occur during sleep as opposed to periods of wakefulness.

The investigation included a detailed assessment of the existing cardiovascular risk factors and/or disease in all participants.

“The results of this study have potentially important clinical implications because they suggest an increased vulnerability to nocturnal cardiac arrhythmias in individuals with SDB and provide an explanation for the observed increase in sudden nocturnal death recently reported with sleep apnea,” said Dr. Mehra.